Evaluating Fire Shelter Performance in Experimental Crown Fires1

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Evaluating fire shelter performance in experimental crown fires1

T. Putnam and B.W. Butler

Abstract: Fire shelters are critical safety items required for use by most wildland firefighters in the United States. Most testing of fire shelters, clothing and other personal protective equipment (PPE) has been limited to prescribed fires or laboratory based studies. This study reports results from experiments where lined and unlined stainless steel or aluminum and glass fabric shelters were tested under high intensity crown fire conditions in and adjacent to experimental burn plots. Firefighter clothing and standard (pre-2003) fire shelters were also tested. Measured shelter surface and air temperatures and thermal impact on firefighter personal protective equipment were used to deduce the survivability of shelter designs and deployment location. Multiple glass and aluminum layered shelters show more promise than stainless steel shelters for improving overall fire shelter survivability. Data collected outside the burn plots generally indicate decreased heating as distance from forest edge increases, supporting the importance of maximizing distance from vegetation for survivability. It is recommended that common experiment protocols be adopted so that future research into fire shelter and PPE performance builds on work-to-date and provides a common basis from which analyses can be completed.

Résumé : Les tentes-abris des pompiers forestiers sont des équipements de sécurité qui doivent être utilisés par la plu- part des pompiers qui combattent les feux de forêt aux États-Unis. Les tests pour les tentes-abris, les vêtements et les autres équipements personnels de protection ont été limités à des brûlages dirigés ou à des études réalisées en labora- toire. Cet article présente les résultats d’expériences où des tentes-abris recouvertes ou non d’acier inoxydable ou d’aluminium et d’autres en toile de verre ont été testées dans des conditions de feu de forte intensité à l’intérieur et à proximité de parcelles brûlées expérimentalement. Les vêtements des pompiers et les tentes-abris standard (avant 2003) ont aussi été testés. Les températures mesurées à la surface des tentes-abris et de l’air, ainsi que l’impact thermique sur les équipements personnels de protection des pompiers ont été utilisés pour déterminer la possibilité de survie des dif- férents types de tentes-abris dans les différents lieux de déploiement. Les tentes-abris recouvertes de couches multiples de toile de verre ou d’aluminium se sont montrées plus prometteuses que les tentes-abris en acier inoxydable pour aug- menter globalement la capacité de survie au feu. Les données prises à l’extérieur des parcelles brûlées indiquent géné- ralement que la chaleur diminue à mesure qu’on s’éloigne de la bordure de la forêt, d’où l’importance de maximiser la distance de la végétation pour la survie. Nous recommandons que des protocoles expérimentaux communs soient adop- tés de telle sorte que les futurs travaux de recherche sur la performance des tentes-abris et des équipements personnels de protection s’appuient sur le travail fait à date et fournissent une base commune servant à compléter les analyses. [Traduit par la Rédaction] Putnam and Butler 1615

Introduction proved design (Anderson 2003). Use of fire shelters in the United States saves about 14 lives per year (Putnam 1996). Fire shelters are critical firefighter personal protection In addition, fire shelters and fire resistant clothing prevent equipment (PPE). The basic design of the fire shelter, re- more serious injuries for another 25 persons a year (Putnam, ferred to herein as the standard fire shelter (STD), was de- 1996). Fire shelters are the primary protection against veloped, approved, and maintained by the USDA Forest extreme radiant heat and limited flame contact when fire- Service through design specifications until 2003. Experime- fighters cannot escape the fire. This paper reports on experi- nts reported herein tested both the STD (pre-2003) shelter ments where fire shelters were exposed to experimental fires and other prototype shelters that eventually led to a new ap- conducted as part of the International Crown Fire Modelling

Received 14 October 2003. Accepted 11 May 2004. Published on the NRC Research Press Web site at http://cjfr.nrc.ca on 24 August 2004. T. Putnam.2 USDA Forest Service, Missoula Technology and Development Center, 5785 Hwy 10 W, Missoula, MT 59808, USA. B.W. Butler. USDA Forest Service, Fire Sciences Laboratory, Rocky Mountain Research Station, Fire Behavior Research Work Unit, P.O. Box 8089, Missoula, MT 59807, USA. 1This article is one of a selection of papers published in this Special Issue on The International Crown Fire Modelling Experiment (ICFME) in Canada’s Northwest Territories: Advancing the Science of Fire Behaviour. 2Corresponding author. Current address: Mindful Solutions, 3431 Flicker Lane, Missoula, MT 59804, USA. (e-mail: [email protected]).

Experiment (ICFME) in the Northwest Territories, Canada, South Canyon Fire (Butler et al. 1998), firefighters stopped in the summers of 1997 and 1998 (Stocks et al. 2004). before reaching a safety or survival zone and did not sur- The pre-2003 STD in use by wildland firefighters in the vive. Quantitative data were needed to better characterize USA was constructed of aluminum foil bonded to glass cloth survival zones by determining external fire conditions where with an adhesive. Fire shelter performance as a function of the standard shelters were likely to protect the occupant the associated fire environments, based on available data from injury. Postfire entrapment investigations have sug- from 1958–1997, has been summarized (Butler and Putnam gested survival zone characteristics, i.e., minimal flame con- 2001). Fire shelter use and design limitations are summa- tact and fuels, but no specific recommendations have been rized in training booklets for wildland firefighters (Putnam made such as those proposed by Butler and Cohen for safety 1995, 1996). This design provides effective protection in zones. Flame resistant fire shelter designs would effectively high radiant heat environments but only limited protection increase the probability of survival under all conditions. Butler when subjected to direct flame contact. Prior to 1990, fire and Putnam (2001) reported internal air and material tem- shelter designs based on single and multiple layers of peratures inside fire shelters as well as external temperatures 845 °C to 1600 °C glass cloth, metal foils, and intumescent and radiant heat loads. That research suggested two criteria coatings were proposed that could protect against direct for defining fire shelter survival capability: internal surface flame contact. These designs were not funded, largely owing temperature and internal air temperature. If shelter materials to the lack of any known clear failure of the standard fire are likely to contact occupants, then inner surfaces should shelter design and because of the cost, bulk, and weight of not produce conductive burns. For all shelters, a breathable high temperature glass cloth. Intumescent coatings were air temperature is vital. The data are limited, but generally found to produce toxic fumes which could collect inside a indicate that breathing dry 300 °C air will cause burns at the fire shelter. High temperature foils such as stainless steel larynx in a few minutes (SFPE 1995). Such inhalation burns were stiff and not readily available. occur after corresponding burns to the face or skin. Higher The entrapment and death of six firefighters on the Dude air relative humidity values result in more rapid and severe Fire in 1990 near Payson, Arizona, (Tonto National Forest burn injury. Veghte (1986) indicates that bareheaded sub- 1990) led to an effort in 1991 to redesign the fire shelter jects wearing protective clothing were able to withstand air with the main emphasis on finding and testing higher temperatures as high as 205 °C for 4 min. Callin (1969) temperature adhesives. In 1994, on the South Canyon Fire stated that subjects exposed to hot, dry air (less than 1% rel- (Butler et al. 1998) fourteen firefighters died, two possibly ative humidity) averaged 10.5 min at 149 °C and 5.3 min at because of shelter failures, leading to a renewed search for 173 °C before terminating the experiment. Callin further fire shelters that could survive direct flame contact. The stated that breathing hot air was not the limiting factor in his ICFME provided a more realistic fire environment for test- experiment. Putnam (1996) summarized some of the avail- ing direct flame fire shelters. able research and stated that humans can survive and per- In 1993, the first consensus standard for wildland fire- form simple tasks in 150 °C dry air for 10 min, 205 °C dry fighter PPE was approved by the National Fire Protection air for 5 min, and 260 °C dry air for 2 min. In a shelter con- Association (NFPA) and included efforts by federal, state, text, simple tasks would include pushing the shelter fabric and private agencies including structural and wildland off your back and changing body position. For this study an firefighters. NFPA adopted the standard fire shelter as the air temperature above 200 °C for more than 5 min was de- only certifiable fire shelter (NFPA 1993). The NFPA fined as a design failure. The published studies suggest that Wildland Fire Technical committee was subsequently given actual survival times are somewhat longer. the task to determine performance standards for fire shelters; When temperature and exposure energy were not mea- the standard fire shelter would represent the minimum per- sured, they were estimated based on known dye sublimation, formance level. In a separate, related effort the National scorch, stiffening, melt, char, and ignition temperatures and Wildfire Coordinating Group (NWCG), representing most necessary exposure energies for the thermal degradation of federal and state firefighting agencies in the USA, required various materials in a similar manner to that presented in that shelters be capable of holding two firefighters, have a Butler and Putnam (2001). Table 1 (Veghte 1985) is an ex- symmetrical design (no head or foot end), that one size fit ample of such information that has been collected by the all firefighters and specified weight and cost limits. Require- first author and used in entrapment investigations. ments from both these national standard-setting groups limited our shelter designs, experiments, and types of data gathered at ICFME to those that could meet both NFPA and Materials and methods NWCG criteria. Both these agencies wanted data collected to establish the performance of the approved design and de- Test Site Description termine standards for future fire shelter designs. A historical review, scientific scope, and specific site de- Two types of deployment zones where shelters may be tails of the International Crown Fire Modeling Experiment used include (i) safety zones, where firefighters do not ex- are available elsewhere (Stocks et al. 2004). pect to need a shelter but keep one close at hand; and During the crown fire experiments, fire shelters were (ii) survival zones, where firefighters need a shelter and ex- placed both inside and outside the burn plots. Shelters lo- pect everyone to survive (Putnam 1996). In 1998, a theoreti- cated inside the plot boundaries were typically located near cal model of safety zone size was proposed (Butler and the plot centerline near the downwind edge of the plot as Cohen 1998). Guidelines defining effective survival zone shown in Fig. 1. Plots A, 5, and 6 had north to south orienta- size are crucial to firefighter’s safety, for example, on the tions, while plots 7 and 8 had northeast to southwest orienta-

Table 1. Thermal response of 150 g·m–2 Nomex Air Force flight 2004). Strips of fire shelter material were sewn to the inside suit. and outside surfaces to form channels for routing thermocouple wires to the ground. Thermocouple beads were Exposure energy –2 placed in contact with the respective surfaces. Aluminum (cal·cm ) Effect on fabric tape was placed 2–3 cm below the beads to promote surface 3.0 Dye discoloration contact. When shelters had liners, the inner thermocouples 3.4 Dye discoloration were placed on the innermost surface of the liner opposite 4.0 Increased dye loss, probably through the sensors located on the exterior surface. Shelters placed sublimation inside burn plots were located on existing fuels after clear- 4.4 First evidence of fabric shrinkage, slight ing away ground fuels such as logs and larger sticks. The scorch, noticeable stiffening shelters were placed over aluminum (1997) or steel (1998) 5.0 Further dye discoloration, first signs of “A” frames, which supported the shelters during the testing. fabric scorch, very slight stiffening Shelter end and side ground flaps were held down with con- 6.0 Increased shrinkage and scorching, consider- tinuous steel chain or rocks placed at least every 20 cm able stiffening around the inside the shelter at the wall–ground flap joining 8.0 All the above, first signs of charring seam. Video cameras placed inside fire-resistant enclosures 10.0 More charring, first evidence of foaming (Kautz 1997) were positioned to record fire shelter performance during the flame front passage. Pre- and postfire doc- Fig. 1. General test setup. umentation of the test setups included extensive still and video photography. These images recorded the thermal degradation indicated by changes in the color, texture, or struc- ture of the material. Some of the data was provided to the authors by Jim Roth of Storm King Mountain Technologies (Camarillo, Calif.) and by Mark Ackerman of the University of Alberta (Ackerman, 1999). STD shelters used by other experimenters had 18-cm wide ground flaps, whereas those used by the United States Forest Service (USFS) had 46-cm wide flaps. References to Roth’s STD shelters are for shelters set up by him. Roth’s data3 was provided in graphical form and therefore values were estimated from his graphs. Deviations from the general test setup are reported separately under each experimental burn plot. Table 2 summarizes the acro- nyms used to identify shelter type and measured location.

Results Tables 3–8 compare general environmental conditions and fire behavior for each experiment; additional details about tions. Other shelters, clothed mannequins, wooden walls, test conditions and fire intensity can be found elsewhere etc. were located in the clearing on the lee edge of the plot. (Stocks et al. 2004; Butler et al. 2004). The data are presented in chronological order rather than by plot number. General Test Setup For each plot, we first discuss the specific location and lay- Fire shelters for all experiments were instrumented to re- out of individual fire shelters and other protective equip- cord inside and outside surface temperatures on both the foot ment. Next, the data for shelters located inside the plot are end (end towards oncoming fire) and on the left side from discussed, followed by data for shelters and equipment lo- the perspective of a shelter occupant. Shelter surface temper- cated outside the plot. An analysis of the data trends for ature sensors were placed 30 cm, vertically, off the ground. each plot is then presented. These sensors are referred to as foot end outside (FO), foot end inside (FI), side outside (SO), and side inside (SI). Fire Plot A: 1 July 1997 shelter internal air temperatures were measured 5 cm and PlotAwas75m×75mandwasburned with a south 30 cm off the ground at the longitudinal centerline about wind of 16 km·h–1 that was parallel to the plot’s east and 50 cm from the head end of the shelter. Surface temperatures west edges. The USFS set up a standard aluminized glass were recorded with type K thermocouples (nominally (STD) radiant heat shelter and a stainless steel (SS) direct 0.7 mm bead diameter) and air temperatures were recorded flame shelter; and Roth set up a Storm King Mountain with finer (nominally 0.13 mm bead diameter) type K ther- (SKM) shelter inside the plot. Both shelters were located mocouples. An analysis of thermocouple measurement accu- 18 m from the plot edge, midway between east and west plot racy is presented elsewhere (Shaddix 1998; Butler et al. edges. A STD shelter, two clothed mannequins, and other

3 Supplied by Jim Roth, Storm King Mountain Technology, Camarillo, Calif.

Table 2. List of shelter codes and descriptions. Code Description STD Standard USFS, NFPA (pre-2003) certified shelter with 46-cm flaps of aluminum foil bonded to fiberglass cloth SS Same as STD, except constructed of stainless steel foil SSC SS shelter with carbon fabric liner SS+STD SS shelter with STD underneath it as a liner SS+SS SS shelter with SS underneath it as a liner SS2K SS shelter lined with 2 layers of Kapton™ film SS2KAL SS shelter lined with 2 layers of aluminum coated Kapton™ film SS2KTI SS shelter lined with 2 layers of titanium coated Kapton™ film SSHAL SS shelter with AL liner hanging from webbing sewn to ridgeline SKM Multi-layered glass and aluminum foil shelter made by Storm King Technologies SS1.5 Number with any of the above codes represents distance (m) of shelter from burn plot edge FO Foot outside: thermocouple on outside shelter surface at end facing plot and fire FI Foot inside: thermocouple on inside shelter surface at foot end SO Side outside: thermocouple on outside shelter surface on left side SI Side inside: thermocouple on inside shelter surface on left side 5 cm Air temperature thermocouple 5 cm above ground, centered, 50 cm from shelter head end 30 cm Air temperature thermocouple 30 cm above ground, centered, 50 cm from shelter head end

Table 3. Test environment conditions for different burn days. Air temp. Relative 10-m wind Rate of Peak radiant Peak air temp. at Plot (°C) humidity (%) speed (km·h–1) spread (m·s–1) flux (kW·m–2) ground surface (°C) A 22 28 15.8 0.93 300 950 5 21 37 12.9 0.48a 350 1000 6 24 44 16.9 0.6 400 1200 8 30 26 10.8–14b 0.4–0.9 120 — 7 30 38 16.9 1.15 250 780 aDiagonal spread pattern. bWinds decreased and then reformed when fire was midway through plot.

PPE were set up or laid on the ground 2–4 m from the edge black was mostly on the seams it may have been due to of the plot. gases leaking out from inside the shelter. This shelter was very fragile when lifted during the postfire inspection. The Results inner Nomex™ cloth layer was charred brown to black indi- STD shelter temperatures peaked around 1000 °C. The cating temperatures near 440 °C. The ground was lightly shelter melted and collapsed onto the ground in a downwind scorched with a tar residue coating, indicating heavy smoke direction. The temperature and video data show the shelter concentration during the burn over. The glass cloth layers surface melted approximately 7–10 s after flame contact. started falling apart upon handling. The inside breathing The 1 mm tubular aluminum tent frame also melted (660 °C zone temperature peaked at 110 °C for about 100 s. This air melting temperature) but the 5 cm and 30 cm aluminum temperature is survivable but the evidence of the heavy thermocouple tubes and aluminum ground stakes did not smoke, most likely from the Nomex™ degradation, suggests melt indicating the cooling by the ground and lower flame a person under the SKM shelter would have suffered from temperatures near the ground surface. Thicker shelter seams smoke inhalation. The small shelter size and the drooping of were still intact, though fragile. All data indicate a non- the inner fabric surface can expose an occupant to possible survivable shelter. The SS shelter turned uniformly gray in conductive burns. color and was fully erect with no foil melting (approximate Items placed outside Plot A included a STD shelter with a melting temperature 1425 °C). The aluminum tent frame in- simulated skin sensor device inside. The flames and fire side the shelter melted and collapsed. The ground under the whirl that exited the plot destroyed the STD shelter. The de- SS Shelter was charred. The videotape showed the entire vice placed under the shelter ignited and continued to burn flame front propagation sequence: radiant ground heating, a for some time after the surrounding fires had subsided. The shower of sparks, ground ignition, and flame front passage. shelter was about 2 m from the plot edge. An upright man- Recorded temperature data indicated non-survivable internal nequin with Nomex™ coveralls and a yellow polycarbonate air temperatures (approximately 800 °C). hard hat was located about 4 m outside the downwind edge The SKM shelter looked “puffed up” with the outer fabric plot edge. It ignited in a few seconds after arrival of the fire starting to flake off, with white to black color. Since the front and was consumed in about 24 s. A similar mannequin

Table 4. Summary of peak temperatures (°C) for all plots. Foot Foot Side Side Internal air Internal air Plot, shelter outside inside outside inside 30 cma 5cma A, STDb 990 925 1050 1020 950 890 A, SS 1080 1000 1055 995 950 805 5, SS 1065 970 1015 945 905 465 5, SSC 1010 925 1010 — 715 690 5, STD3.0 155 22 133 102 51 40 6, SS+SS 995 810 1085 860 750 375 6, SS+STD 1015 660 1095 — 660 240 6, SS1.5 765 720 670 690 505 — 6, STD1.5b 875 805 800 755 — 500 6, STD3.0 740 760 670 645 485 330 7, SS 800 750 805 840 805 770 7, SSHALc 780 760 825 705 655 805 8, SS2K 780 490 690 555 555 495 8, SS2KAL 775 350 690 520 370 250 8, SS2KTIc 760 580 575 590 670 480 8, SS 730 610 690 625 690 590 8, STD2.0b 825 800 680 915 725 565 8, STD4.0 675 390 315 245 220 190 8, STD6.0 410 170 240 155 145 145 8, STD8.0 315 205 220 235 170 185 Note: See Table 2 for shelter codes. aMeasured above ground level. bShelter melted open. cShelter split open. was located on the ground with the feet 2.5 meters from the ground peaked at 1020 °C and were above 200 °C for about edge of the plot. This mannequin also had on a pair of 50 s. The air temperature sensor located 5-cm high in the gloves, a pair of leather boots with Vibram™ soles and a stainless steel (SS) shelter stayed above 200 °C for 152 s, in- blue hard hat. These items were almost completely con- dicating that the shelter retained heat after the ground out- sumed during the flame front and subsequent burning. Other side had started to cool. The video showed the STD shelter ground items were a nylon field pack, a chrome tanned was consumed by the fire in about 6–10 s. The SKM FO leather glove, a polyethylene canteen and a 20-L filled water temperature peaked at about 950 °C followed by SO, SI, and bag enclosed in a cotton t-shirt and standard USFS FI temperatures that all followed the same curve upward and Nomex™ fire shirt. Most of these items were completely peaked at about 600 °C. The 5 cm high inside air tempera- consumed except for the Vibram™ soles and some layers of ture peaked at 110 °C and stayed above 100 °C for about fire shirt material next to the cotton t-shirt or under the wa- 100 s (similar to the time for cooling outside the shelter). It is ter bag, which were partially consumed. The video showed not clear why the SO temperature peaked 345 °C below the the number of seconds between arrival of the flames and ig- foot outside. The SKM shelter showed an outside-to-inside nition were: 3 s for the clothing and shelter, 5 s for the nylon temperature drop of about 340 °C. Based on internal surface pack and 33 s for the hardhat. The uniformly charred and air temperatures, the SKM provided the most survivable Nomex™ shirt indicates temperatures on the ground in ex- environment. In the previous work by Butler and Putnam cess of 440 °C with a total energy exposure ranging from (2001) the average difference between the cooler 5 cm and 120 cal·cm–2 (for Nomex™ on the water bag) to 360 cal·cm–2 the warmer 25 cm air temperatures was 35 °C (20–70 °C (for Nomex™ on the mannequin). The video footage indi- range). For this study the difference for the SS shelter was cated flame contact duration of 27 s, suggesting an average 40 °C and for the SKM shelter the difference was 195 °C. heat flux of 9 cal·cm–2·s–1 or 360 kW·m–2. The SKM difference may be due to the Nomex™ liner con- tacting the upper air thermocouple. Video footage indicated Analysis that the shelter and PPE outside the plot were exposed to The external surface temperatures (FO and SO) of the about 27 s of flame, the same duration as inside the plot. A STD and SS shelters started increasing first. They were fol- nearby radiometer recorded a peak heat flux of 400 kW·m–2. lowed 7 s later by the rise in the internal surface tempera- Most of the flames coming out of the plot were centered tures (FI and SI). Temperatures peaked at 925–1080 °C. For over the setup equipment, extending 10 to 15 m to either the SS shelter, the 5-cm and 30-cm high inside air tempera- side. tures peaked at 800–950 °C and started to cool off quicker than the surface temperatures. Temperature data from a ver- Conclusions tical array of sensors near the shelter showed outside tem- This burn confirmed many expectations: (i) the STD shel- peratures peaked at 1100 °C. Temperatures close to the ter will not survive prolonged direct flame contact; (ii)aSS

Table 5. Summary of average temperatures (°C) for all plots. Foot Foot Side Side Internal air Internal air Time FO over Plot, shelter outside inside outside inside 30 cma 5cma 100 °C (s) A, STDb 305 340 271 266 167 184 222 A, SS 294 353 358 351 309 270 210 5, SS 237 154 210 161 — 212 508 5, SSC 206 338 254 — 303 236 236 5, STD3.0 127 22 87 81 39 34 40 6, SS+SS 307 315 287 310 300 175 174 6, SS+STD 295 323 361 — 231 139 132 6, SS1.5 241 265 206 228 207 22 148 6, STD1.5b 325 302 308 292 — 183 72 6, STD3.0 284 280 272 257 187 160 74 7, SS 231 262 199 246 226 260 231 7, SSHALc 210 168 160 121 161 152 462 8, SS2K 262 279 275 279 245 267 145 8, SS2KAL 259 199 194 — 178 140 185 8, SS2KTIc 303 292 266 197 269 287 99 8, SS 246 272 206 245 219 244 193 8, STD2.0b 238 232 199 — 129 144 152 8, STD4.0 230 174 172 146 133 129 102 8, STD6.0 182 127 102 117 123 109 104 8, STD8.0 165 145 119 125 104 121 106 Note: See Table 2 for shelter codes. aMeasured above ground level. bShelter melted open. cShelter split open. shelter will withstand direct flames but without liners they Results are too hot for survival; and (iii) the SKM shelter, with mul- Both SS and SSC shelters turned uniformly gray color. tiple layers, would be closest to surviving this flame front. Aluminum tent frames inside both shelters partially melted Unexpected results include: (i) the fire video inside the plot and collapsed. Temperature data showed similar external showing the sequential radiant heating, fire brand dispersion, temperatures for the two shelters. Internal maximum temper- and flame front propagation for the first time ever in a atures were similar with some variation observed in the heat- wildland environment; (ii) radiant heat fluxes 240– ing start times. The lined SSC shelter had low internal 400 kW·m–2;(iii) measured air temperatures up to 1350 °C; temperatures followed by an extremely rapid temperature and (iv) the way the flame front exited the plot in a very lo- rise. Postfire examination indicated that at some point the calized area with fire whirls and prolonged flame duration carbon liner had fallen away from the SSC shell. The SSC compared with the rest of the plot edge. internal 5-cm air temperature peaked higher than the 5-cm measurement in the SS shelter, likely owing to the sensor being in contact with the carbon liner when it fell away from Plot 5: 4 July 1997 the shell. The liner effect can be seen by comparing total Plot 5 was 150 m × 150 m and was burned with a wind of heat loads calculated as the product of the average 5-cm air 13 km·h–1. A stainless steel shelter with a carbon fabric liner temperature (Table 5) and the time that the sensor on the ex- (SSC) and an unlined control shelter (SS) were set up inside ternal surface of the foot end of the shelter exceeded 100 °C the plot about 23 m from the leeward edge of the plot and (i.e., 107 696 °C-s (degree-second) for SS and 55 696 °C-s 50 m from the northwest plot corner. Two standard shelters for SSC). Neither of these shelters was survivable based on and other protective equipment (PPE) were placed on the internal air temperatures. Ground fuels underneath the SS ground surface outside the plot, 3 m and 6 m from the down- shelter were charred black in the center and less severely wind plot edge. PPE included a Nomex™ shirt, a hardhat, a charred under the shelter floor flaps. Vegetation under the piece of folded cotton cloth, a plastic canteen, leather carbon liner of the SSC shelter was still green, though gloves, and a PVC shelter bag. Another research group charred where the liner did not cover it. (Ackerman, Dakin, and Roth) placed shelters and PPE out- The wind was not aligned with the primary axis of the side the plot about 60 m from the northeast plot corner. plot, resulting in the fire exiting the near the corner of the Their shelters were, from east to west, a STD shelter with its plot. The quartering of the fire across the plot meant that the side parallel to the edge, 1.2 m out from the plot edge (there- two STD shelters received no flame contact, only radiant fore STD1.2P). Other shelters were oriented with the foot heat. The shelter at6mwasnotinstrumented and received end towards the plot: STD2.4, STD1.2, STD 4.9, SKM1.2 no damage. The PPE at this location received little damage and SKM2.4. Data from these shelters was provided by except a few spots on the fabrics that showed charring, prob- Roth. ably because of falling embers. For the shelter at 3 m, the

Table 6. Summary of the number of seconds that internal air and both peak at about 470 °C. This suggests the SO and temperatures (measured above ground level) stayed over 200 °C 30 cm leads may have been reversed, in which case the data and 100 °C. follows the same pattern as Roth’s other figures. In comparison, the STD2.4 shelter shows a normal set of data with the Over 200 °C (s) Over 100 °C (s) FO and SO leading and peaking at 920 °C. Internal air tem- Plot, shelter 30 cm 5 cm 30 cm 5 cm FO peratures lagged about 17 s behind and both the 5-cm and A, STDa 54 61 183 163 222 30-cm air temperature sensors peaked about 480 °C. The 5-cm A, SS 156 152 240 240 210 air temperature was above 200 °C for about 30 s. While 5, SS 112 124 421 424 508 these temperatures exceed the design criterion selected for 5, SSC 205 160 480 407 236 this study, the authors speculate that an occupant in the shel- 5, STD3.0 0 0 0 0 40 ter may have survived if they had pressed their face to the 6, SS+SS 129 57 327 208 174 ground where they would likely have been able to breathe 6, SS+STD 94 19 191 147 132 the ground-cooled air during the time that the internal air 6, SS1.5 53 — 188 — 148 temperatures exceeded 200 °C. The SKM1.2 shelter showed 6, STD1.5a — 27 — 81 72 extensive thermal damage at the foot end and the FO data 6, STD3.0 23 18 59 60 74 failed to record. The SO temperature rose quickest and 7, SS 93 101 426 402 231 peaked at 650 °C. The SI temperature followed and peaked 7, SSHALb 148 90 266 241 462 at 180 °C. The 5-cm air temperature rose slowest, with 8, SS2K 109 119 280 289 145 about a 40 s time delay, and peaked at 120 °C. Internal air 8, SS2KAL 67 27 223 173 185 temperatures were well within survivable ranges. Tempera- 8, SS2KTIb 73 105 207 205 99 tures dropped faster outside the SKM shelter than under it. 8, SS 73 84 246 248 193 The data from the SKM2.4 shelter showed much cooler tem- 8, STD2.0a 29 24 96 98 152 peratures than encountered by the other shelters in this area. 8, STD4.0 7 0 88 98 102 The FO data were lost and the SI temperatures rose first and 8, STD6.0 0 0 71 80 104 peaked at 375 °C. The FI temperature peaked at 300 °C. The 8, STD8.0 0 0 64 86 106 5-cm air temperature peaked at 60 °C. Note: Foot outside temperature (FO) is above 100 °C for all USFS shelters. See Table 2 for shelter codes. Conclusions aShelter melted open. bShelter split open. The installation of a carbon fabric liner in an SS shelter showed that until it fell loose, the liner substantially reduced peak FO temperature was about 150 °C. SO and SI tempera- internal shelter air temperatures. It also showed that even tures peaked at 125 °C and 100 °C respectively. Internal air fabrics with melting temperatures as high as carbon can fail temperatures peaked at about 50 °C. PPE on the ground at because of loss of structural integrity. Outside the plot, the 3 m showed light melting (canteen, PVC bag, and hardhat STD shelters performed well, since they were not subjected melting point nominally 135–165 °C). The Nomex™ shirt to direct flame contact. The PPE on the ground at the 6 m showed little thermal degradation except for light scorching location showed very little thermal damage, whereas the at fabric folds higher off the ground (~300 °C) and multiple PPE at 3 m showed melting (plastics), browning (Nomex™), scorched spots from embers. The cotton fabric had ignited. and consumption (cotton) suggesting thata3mdifference in Temperature and heat flux measurements inside the shelters separation from the vegetation can significantly change suggest that occupants inside shelters at this location would chances for survival. The data also suggest that Nomex™ have survived the internal shelter temperatures without in- fabrics provide increased protection, as compared with cot- jury. At the 6-m location a person outside a shelter should ton fabrics, from moderate radiant heat and falling embers. have had no injury and at3maperson without a shelter When the brief flame contact occurred, the Roth STD would have had light, first-degree burns. shelters nearest the plot edge quickly delaminated and the aluminum melted exposing the clothing under the shelter to Analysis higher heating. The SKM shelters at the same distances suf- The outside shell temperatures started rising first, closely fered light damage and remained intact. When all the data followed by the inside shell temperatures. Internal air tem- reported by Roth at this site is compared, there is a definite peratures showed the same rise but of a lower magnitude, drop in temperatures in a downwind, east-to-west direction. and exhibited a 20–30 s time lag behind the external values. This effect could be due to temperatures cooling further out The outside shell temperatures decreased the soonest with of the plot or to STD shelters further east shielding other slower cooling under the shelters. The liner delayed the on- STD shelters and all the STDs shielding the SKMs to some set of temperature rise inside the shelter until it fell away. degree. Careful analysis of the data showed the STD shelters The STD3.0 outside the plot showed the FO temperature lasted long enough to give potential occupants a chance to peaked at 155 °C with lower values for the other sensors as survive. Many firefighters in Nomex™ clothing have sur- shown in Table 4. The SKM shelters were exposed to direct vived entrapments with their clothing significantly more flame contact. For the STD1.2P shelter, Roth’s data show damaged than the Nomex™ clothing placed under shelters the 30-cm air temperature starting to rise before the outside STD1.2 and STD2.4. The difference in the thermal damage shell temperatures and peaking at 850 °C; the outer shell to clothing under shelter STD1.2P versus STD1.2 showed temperature and 5-cm air temperature show similar curves the benefits of keeping your feet towards the oncoming fire.

Table 7. Summary of shelter damage, PPE damage, and expected injury for all USFS shelters. Plot Shelter Shelter damage PPE damage Expected injury w/o shelter Expected injury with shelter A STDa Melted into ground NA Death Death A SS Color change NA Death Death 5 SS Color change NA Death Death 5 SSC Color change and carbon NA Death Death liner fell to ground with some charring 5 STD3.0 None NA 1st degree burns No injury 5 STD6.2 None NA No injury No injury 6 SS1.5 Rainbow color NA Death Death 6 SS+SS All gray color NA Death Death 6 SS+STD All gray color NA Death 3rd degree burns 6 STD1.5a Foot end melted NA Death Death 6 STD3.0 Foot and side foil melted NA Death Death 6 STD4.6 Foot end foil melted NA Death Death likely 7 SS — Death Death 7 SSHALb — Death Death 8 SS Mostly gray NA Death Death 8 SS2K Mostly gray, liner charred NA Death Death 8 SS2KAL Mostly gray, liner charred NA Death Death 8 SS2KTIb Mostly gray, liner charred NA Death Death 8 STD2.0a Foot end melted away Nomex dark brown Death 3rd degree burns or death 8 STD4.0 Light foil melting No damage Death No injury 8 STD6.0 Brown inside No damage 2nd and 3rd degree burns No Injury 8 STD8.0 Light foil melting No damage 3rd degree burns No injury Note: NA, no data available. See Table 2 for shelter codes. aShelter melted open. bShelter split open.

Table 8. Summary of shelter damage, PPE damage, and expected injury for experiments set up by non-USFS personnel. Expected burn injury Plot Shelter Shelter damage PPE damage W/o shelter With shelter A STD2.0 Melted into ground Nomex charred black Death Death 5 STD1.2P Mostly melted Nomex charred black Death Death likely 5 STD2.5 Mostly melted Nomex mostly scorched Death likely 2nd degree burns 5 STD1.2 Mostly melted Nomex charred and scorched Death likely 3rd degree burns 5 STD4.9 Light brown inside NA 2nd degree burns No injury 5 SKM1.2 Nomex light char Coveralls ok, plastic melted Death 1st–2nd degree burns 5 SKM2.5 Nomex mostly ok NA Death likely No injury 6 SKM Nomex light char NA Death 2nd–3rd degree burns 6 STD1.2 No damage NA 2nd and 3rd degree burns No injury 6 SKM1.2 Nomex scorched NA 2nd and 3rd degree burns No injury 8 SKM Minor damage NA Death NA 8 SKMAL Mostly melted, glass pliable NA Death Death 8 STD Mostly melted, glass fragile NA Death Death 8 SKM3.0 Blackened glass NA Death 1st degree burns 7 STD5.0 No damage NA 2nd degree burns No injury 7 STD7.0 No damage NA 1st and 2nd degree burns No injury Note: NA, no data available. See Table 2 for shelter codes.

STD1.2P with its side parallel to the oncoming fire suffered The SKM1.2 shelter held up well to the shorter duration greater damage (i.e., more shelter melt damage and greater flames. Postfire inspection revealed tar residue on the cooler damage to the clothing underneath). Rubber boots ignite and plastic articles under the shelter. We attribute this vapor de- continue to burn more readily than boots with Vibram ™ position to off-gassing by the Nomex™ inner liner as it de- soles and chrome tanned leather uppers. Much of the char- graded. The Nomex™ was used as an inner liner to help ring of the Nomex™ coverall leg bottoms was due to the block conductive heat, since the smaller SKM shelter has burning rubber boots, which present an additional hazard. greater potential for contact burns. Failure of both the

Fig. 2. Stainless steel shelter with a stainless steel liner (1997, Fig. 3. Stainless steel shelter with a standard shelter liner (1997, Plot 6). Plot 6).

Nomex™ and carbon fabrics at this site suggests that fabrics with less heat resistance than glass cloth are unsuitable for carbon liner. Since the SS data for Plots A and 5 were simi- fire shelter construction. lar, no SS was set up as a control. A vertical array of thermocouples was located next to the SS + SS, and both Plot 6: 9 July 1997 shelters were videotaped. Both the outer SS shells turned Plot 6 was 150 m × 150 m and was burned with a wind of uniformly gray color on the outside. The video footage sho- 17 km·h–1. A SS with another SS inside (SS + SS) and a SS wed that the main flame front made direct contact with these with a STD inside (SS + STD) were set up inside the plot shelters. Shelter outside temperatures were 1015–1095 °C, about 28 m from the plot’s south downwind edge and 60 m which were lower than those recorded by the vertical array from the west edge. Outside, near the center of the south of thermocouples (i.e., 1050–1200 °C), possibly because of edge of the plot, a SS and a STD shelter were placed 1.5 m some initial reflectance of the SS foil (Figs. 2 and 3). Both from the plot edge with 2 other STD shelters 3.0 m and of these double-wall shelters showed a significant reduction 4.6 m from the plot edge. PPE was placed on the ground in internal temperatures with the SS + STD showing the 4 m from the plot edge and consisted of a Nomex™ shirt, greatest reduction (Table 9), likely because of the higher re- plastic hardhat, nylon pack, leather glove, and cotton cloth. flective surface of the STD shelter. Visual inspection of the The outside shelters were designated SS1.5, STD1.5, STD3, ground and vegetation under the shelters after the fire indi- and STD4.6, respectively. cated little drying or charring, with the least under the SS + Shelters set up by Roth included an SKM shelter inside STD shelter. The SKM shelter placed in the lighter fuels the plot 15 m from the plot’s south edge and 25 m from the showed some damage but significantly less than the SKM plot’s east edge. This was an open, mossy area with lighter inside Plot A. The outside temperature peaked at 870 °C fuels than the locations where the lined SS shelters were which was about 200 °C less than for the SS shelters inside setup. Outside the plot, Roth set up a STD and a SKM shel- the plot. The ground under this shelter had some charring ter side-by-side, 1.2 m from the plot’s south edge and about near the foot end and was otherwise green. The inner shelter 30 m from the plot’s east edge. These three shelters were Nomex™ layer had some black char along the foot end designated SKM, STD1.2, and SKM1.2 respectively. No ridgeline and light brown scorching over 50% of the inner clothing was placed under any of the shelters on Plot 6 ow- surface nearest the foot end. ing to insufficient setup time before ignition. There were significantly less flames where Roth set shelters up outside the plot. The SKM1.2 FO temperature Results peaked at 850 °C as did the SKM inside the plot, but the The two USFS shelters inside the plot were SS shelters SKM1.2 SO temperature peaked at 250 °C versus 870 °C for “lined” with a second SS or STD shelter to continue to test the SKM SO. The SKM1.2 had light end damage, whereas the hypothesis that the SSC shelter on Plot 5 showed a defi- the STD1.2 had no damage on the exterior. The SKM1.2 had nite temperature lowering effect attributable to the liner. light brown scorching on the foot end interior and the STD These liners have a higher degradation temperature than the shelter had no damage on the interior. Based on the postfire

Table 9. Plot 6 peak and average temperatures (°C) for lined time the internal air temperatures were above 200 °C is shelters. informative. Since the SS + STD 30-cm air temperature exceeded 200 °C for 94 s, and the 5-cm (nose area) tempera- SS (Plot 5) SS+SS SS+STD SKM ture exceeded 200 °C for 19 s, a person under this shelter FO 1080 1000 1000 870 may have survived (based only on the criteria of air temper- FI 960 800 660 — ature over 200 °C for less than 5 min). SO 1000 1100 1100 870 The SKM showed even lower internal temperatures, SI 950 850 — 240 though exposed to cooler temperatures. The brown scorch 30-cm peak 900 750 660 120 and black char on the SKM inner surface indicated tempera- 5-cm peak 450 370 240 210 tures in the 300–600 °C range, although the SI temperature 30-cm average — 300 231 — peaked at 240 °C. The SI temperature sensor was placed be- 5-cm average 212 175 139 — tween quilt lines where the fabric sags, possibly resulting in FO>100 °C (s)a 508 174 132 — cooler readings. Outside foot temperatures were above 200 °C for 150 s for SKM and 200 s for SKM1.2. All inside Note: See Table 2 for list of codes. Average temperatures were calcu- temperatures were below 100 °C, indicating a high probabil- lated for the time FO remained above 100 °C. aNumber of seconds that FO exceeded 100 °C. ity of survival. Since the foot end of the SKM had light damage but the STD1.2 nearby had no damage, this would indicate longer duration radiant heating. The STD shelter ap- analysis, we conclude that occupants in either shelter would pears to out-perform the SKM shelter in high radiant heat have survived without injury. environments with only brief flame contact. At the location where the USFS shelters were placed out- Shelters were set up outside the plot, 1.5m from the plot’s side the plot, video imagery shows that flames came out of edge, to contrast STD and SS performance under brief flame the plot about 10 m, igniting a nearby wood wall (Cohen contact. Additional STD shelters at 3.0 and 4.6 m were in- 2004), hooked towards the shelters to the east, but did not tended to provide information on the effect of decreasing produce a fire whirl. The SS and STD shelters at this loca- thermal damage to shelters as a function of distance from tion had brief flame contact. The SS1.5 shelter turned a dark the heat source (edge of plot). A comparison of STD1.5, 3, rainbow color (~680 °C) on the east side and a gray color and 4.6 (see Table 10) provides quantitative data that could with rainbow tones on the hotter west side and foot end be used in predicting the size of survival zones. Since there (~750 °C). The inside showed lighter rainbow colors was insufficient time to instrument STD4.6, thermal values (~600 °C). In contrast, the STD1.5 peaked at 875 °C on the were estimated based on visible temperature indicators such foot end, well above the aluminum melting temperature of as melting and scorching. The SS1.5 performed better than 660 °C and the glass melting temperature of 730 °C. At the STD1.5 owing to the STD1.5 end breaking open and be- foot end of the STD1.5 shelter, the aluminum tent frame cause the STD1.5 was closer to the flames that came 10 m melted and fell to the ground 5 s after flame contact, then out of the plot. As the distance from the plot edge increased, the rest of the shelter delaminated and peeled back, leaving the temperatures on the surface and inside the shelters de- aluminum foil only on the head end. About 75% of the glass creased, as shown in Fig. 4. The amount of foil damage also at the foot end was white in color, showing the adhesive had decreased: 83% for STD1.5, 75% for STD3.0, and 33% for burned off (~425 °C). The STD3 outer shell temperature STD4.6. The SKM1.2 and STD1.2 shelters located outside peaked at 740 °C on the foot end and 670 °C on the east the SE corner had only brief flame contact. Although closer side. The 5-cm air temperature peaked at 325 °C. The foil to the plot’s edge, STD1.2 in the SE corner had no damage was gone on the east, west, and foot sides, with more signs compared with the damage of STD4.6 showing that within of melting at the foot and west sides. Unlike STD1.5, STD3 the range explored in this experiment, greater distance does was still standing and all the glass cloth was still in place. not ensure less flame contact. About one-third of the shelter at the foot end had turned white with dark brown adhesive remaining on the rest of the shelter (~315 °C). STD4.6 was the farthest shelter out from Conclusions the edge and was not instrumented; the foot end and one- Shelters SS + SS and SS + STD showed that another layer third of the foil on the east side were melted. The west side of foil could reduce temperatures and that a highly reflective foil was mostly delaminated but remained in place. The head inner layer was better than a moderately reflective layer. The end was partially delaminated (~260 °C). The glass cloth be- SKM shelter of multiple layers uses this principle but has tween the ends was mostly brown in color (~300 °C). PPE more layers. Both SS + STD and SKM shelters appear to be placed on the ground was on the west side of STD3 about survivable from an air temperature perspective. The smaller 4 m out from the plot edge was mostly consumed. SKM would have greater conductive burn potential owing to less air space between an occupant and the fabric and be- Analysis cause of the tendency of the fabric to fall down without in- The two double-wall shelters inside the plot were set up to ternal supports. Smoke, oxygen, and relative humidity levels determine how much heat reduction the extra layer could were not measured during the flaming and cooling down give. In addition to air as an insulator, the SS lined with a times; therefore only a tentative survivability status can be STD had a highly reflective surface compared with the SS + SS given for these shelters. This was the first time a SKM shel- shelter. The results show that both double-wall shelters sig- ter performed worse than a STD shelter. This is likely due to nificantly reduced internal air temperatures. The length of only very brief flame contact and a longer high radiant heat-

Fig. 4. Survival zone peak temperatures as a function of distance Table 10. Plot 6 peak and average temperatures (°C) at increas- from the plot’s edge for three STD shelters (1997, Plot 6). ing distances from the plot’s edge. SS1.5 STD1.5 STD3.0 STD4.6 FO 770 870 770 ~660 FI 720 800 770 ~600 SO 680 800 660 ~600 SI 690 750 650 ~500 30-cm peak 500 — 490 — 5-cm peak — 500 325 — 30-cm average 207 — 187 — 5-cm average — 183 160 — FO>100 °C (s)a 148 72 74 — Note: Average temperature values were calculated for the time FO remained above 100 °C. See Table 2 for list of codes. aNumber of seconds that FO exceeded 100 °C.

Plot 8: July 4, 1998 Plot 8 was 150 m × 150 m and was burned with a south- east wind averaging 12 km·h–1. The USFS shelters inside the plot were near the center of the plot about 33 m from the northwest plot edge. A SS unlined shelter and three additional SS shelters lined with two layers of 0.025 mm thick Kapton™ film were deployed. There were three types of Kapton™ film: uncoated (K); with a reflective coating of ing period. This experiment suggests SKM shelters could be aluminum (KAL); or with a reflective coating of titanium the worse choice in very high, prolonged radiant heat envi- (KTI). From southwest to northeast, the respective shelters ronments such as the Dillon, Montana, test site reported by were SS2K, SS2KTI, SS2KAL, and SS. The main purpose Butler and Putnam (2001). The survival zone experiment of this shelter experiment was to compare double-lined SS showed decreasing heat and thermal damage as distance shelters with an unlined SS as a control. The Kapton™ ma- from the plot increased (Fig. 4). terial is very thin, light-weight, and flexible with a high temperature degradation limit. As with tests on Plot 6, we 1998 Tests wanted to see whether a reflective surface led to further heat Experiments were planned to collect video, temperature, reduction, so we tested two reflective coatings: aluminum heat, fire sounds, and gas concentration data inside and out- and titanium. side shelters in three scenarios: (i) test lined shelters inside To the immediate northeast, Roth set up a multiple layer the plots, (ii) test for survival zones outside the plots with glass cloth–foil SKM shelter but without the Nomex™ inner STD shelters, and (iii) test safety zone guidelines by com- liner from the 1997 Northwest Territories experiments. Next paring thermal damage to clothed mannequins outside the to the SKM was a shelter that looked like a STD shelter ex- plots (to be reported elsewhere). cept that is was made from a different aluminum foil – glass The SS shelters designed for direct flame contact had lin- laminate; hence it was called SKMAL. The third shelter set ers made from one or two layers of Kapton™ film, which is up by Roth was a STD and it was the furthest to the north- widely used in airline passenger and hotel escape hoods. east. Outside the plot, STD shelters were placed 2, 4, 6, and Some Kapton™ film had reflective coatings. Other SS shel- 8 m from the plot edge and were designated STD2, STD4, ters had liners made from the STD shelter material. A third STD6, and STD8, respectively. Nomex™ clothing was pla- SS shelter also used STD material for the liners, except that ced under each shelter. These shelters were fully instru- the liners hung down from the shelter ridgeline 3 cm with mented and videotaped. Roth also placed an SKM shelter glass webbing. The glass webbing was sewn at the top to the 3 m from the edge, called SKM3. ridgeline of the SS outer shelter and at the bottom to the top of the STD inner shelter. It was expected that this separation Results would decrease the heat conduction between the two shelter Table 11 shows the flame temperatures at this site were layers. The STD Survival Zone experiment was similar to the lowest recorded inside a plot and peaked between Plot 6 in 1997, except the shelters were located further from 730–780 °C. The outer SS shells for all four shelters were the plot’s edge and there were four shelters instead of three. not the uniform gray we had seen on shelters inside Plots A, Nomex™ clothing was placed under these shelters as an ad- 5, and 6 but rather showed silver, rainbow, and gray hues ditional indicator of thermal damage. Shelters were located consistent with lower temperature flames. For the first time, intentionally so that there would be significant damage to two of the SS shelters had seam damage. SS2K had a 200-cm the closest shelter but little or no damage to the furthest open seam on the horizontal lap seam, midway up the side shelter from the plot’s edge. of the shelter. Video footage shows the SS2KTI shelter had

Table 11. Plot 8 (A) peak and average temperatures and (B) sec- the closest of all shelters to the plot edges. More than 70% onds above 100 °C for SS shelters with different liners. of the shelter disintegrated, starting at the foot end. The 30% of the foil remaining at the head end was mostly on the left (A) Peak and average temperatures (°C). side. The Nomex™ pants under this shelter had light to dark SS2K SS2KTI SS2KAL SS2KTI SS brown thermal damage and stiffening (~375 °C) on the top FO 780 760 775 760 730 layer but not the second layer, showing the heat was brief. FI 490 580 350 580 610 Outside temperatures peaked at 825 °C. STD4 was next fur- SO 690 575 690 575 690 thest out. Only the right side of STD4 has foil damage. The SI 555 590 520 590 625 damage is near both corners, so was likely due to secondary 30-cm peak 555 670 370 670 690 ground fires. The damage stopped 20 cm above the ground. 5-cm peak 495 480 250 480 590 Most of the missing foil was blown back by wind turbu- 30-cm average 245 269 178 269 219 lence with little melt damage. The foot end was dark 5-cm average 267 287 140 287 244 brown (~315 °C) with light brown discoloration (~290 °C) on the sides. Outside temperatures peaked at 675 °C on the (B) No. of seconds FO exceeded 100 °C. foot end and 315 °C on the left side. The Nomex™ clothing FO>100 °C 145 99 185 99 193 under STD4 showed no damage. STD6 was next furthest out 5 cm >200 °C 119 105 27 105 84 and had no exterior damage. The underside was darker brown 5 cm >100 °C 289 205 173 205 248 near the ground on the right side with some delamination indicating temperatures of 300 °C. The data for STD6 shows a FO 5-cm delay 28 30 33 30 21 peak FO temperature of 410 °C. The Nomex™ clothing un- Note: Average temperatures values were calculated for the time FO re- derneath was undamaged. The last survival zone shelter, mained above 100 °C. See Table 2 for shelter codes. STD8, had foil damage low to the ground along the right side up to 30 cm off the ground. The foil was melted in the totally split open along the entire ridgeline because of corner at the foot end but most of the foil tore off rather then melted thread 30 s after the flame front arrived. melted off, suggesting strong air turbulence. The underside The ground print for the SS2K shelter showed charring in of the shelter was light brown (~290 °C) at the foot end and the center with non-charred ground under the side flaps. The darker brown on the bottom right edge (~315 °C). Foot end Kapton™ liner was charred at the top where it attached to temperatures peaked at 315 °C showing the ground fire the outer shell ridgeline and at the bottom where it attached came from the right. Nomex™ clothing under this shelter to the outer shell side–flap junction. The ground print for the had no damage. SS2KAL shelter showed all green vegetation. The ground print under the SS2KTI shelter showed mostly green vegeta- Analysis tion. Most of the Kapton™ liner under this shelter charred The direct flame shelter experiments showed that layering and fell to the ground and the pieces protected the ground inside a SS shell reduced internal air temperatures signifi- resulting in spotty charring, but otherwise green vegetation. cantly (Table 11). Since the SS shell remained essentially in In contrast, the SS ground print was all charred. This SS, un- place, conductive burns to a person under this shelter would like previous SS shelters, had ground flaps made from the not be likely. The unlined SS 5-cm air temperature was STD shelter laminate. The laminate was mostly delaminated 590 °C followed by SS2K at 495 °C, showing the layering with the aluminum melted along the side–flap junction effect. An examination of the SS2KTI data indicates that seam. All three Kapton™ liners released a thick smoke upon prior to breaking open, the 5-cm air temperature was 390 °C, charring, which would rule out their use in operational shel- about the same as for SS2KAL, suggesting that the drop ters. The heavy smoke was still present when these shelters from 550 °C (SS2K) to 250 °C (SS2KAL) was due primarily were examined 30–40 min after exposure to the flame front. to the reflective coatings. Comparing all temperatures be- The SKM shelter had minor damage on both the outside and tween SS2KAL and SS2KTI shows that the aluminum coat- inside. We did not receive any data from Roth, so no discus- ing out-performed the titanium coating. Vegetation in the sion of specific temperatures follows. The SKM ground print “ground prints” under the SS was the most charred followed was mostly green. The foil from the SKMAL shelter and the by SS2K, then SS2TKI with mostly green vegetation re- STD shelter next to it was mostly melted away. The SKMAL maining, and finally SS2KAL with all green vegetation. The shelter glass cloth was generally more pliable and the STD time the 5-cm air temperature stayed over 200 °C was 27 s glass cloth more brittle. Of the seven shelters in this group, for aluminized Kapton™ (SS2KAL) versus 119 s for un- only the SKM may have been survivable. The SKMAL and coated Kapton™ (SS2K) indicating less heat storage be- the STD shelters were held down with a few rocks, while the cause of the aluminized coating. The comparative time for SKM was held down on all the edges with continuous, SS2K at 119 s and the unlined SS at 84 s shows faster cool- heavy chain. Bottom edges that are not firmly held down lift ing for SS, since liners tend to hold in accumulated heat af- up in turbulence, allowing heat and flames to come under ter the external temperatures subside. Since all the liners the flaps. charred and fell away, it is not possible to predict what the Roth set up a SKM shelter 3 m from the plot edge. At this temperatures would have been if the liners had not thermally location, the SKM3 had more damage than the SKM inside degraded. There is also a possible shielding effect of the the plot, with significantly more dark black discoloration, shelters as set up or simply cooler flames from the south- particularly on the left side. There were four shelters in the west to northeast. We believe none of the SS lined shelters survival zone experimental group (see Table 12). STD2 was were survivable owing to observations of the thick and likely

Table 12. Plot 8 peak and average temperatures (°C) for four STD2 occurred 13 s after the flames from the unit ended and survival zone shelters. after a ground fire flared. Air temperatures inside the shelters are shown in Table 14 and Fig. 6. The only air tempera- STD2 STD4 STD6 STD8 tures questionable from a survival standpoint are in STD2 FO 825 675 410 315 where the 5-cm air temperature exceeded 200 °C limit for FI 800 390 170 205 29 s and peaked at 915 °C for only a second or two. Surviv- SO 680 315 240 220 ability would mostly depend on whether or not a person SI 915 245 155 235 breathed at that moment. The damage to the Nomex™ under 30-cm peak 725 220 145 170 this shelter is similar to that found on Nomex™ worn by 5-cm peak 565 190 145 185 firefighters who survived entrapments and on others who 30-cm average 129 133 123 104 died, indicating a marginal survival. Closer inspection of the 5-cm average 144 129 109 121 foil damage to the shelters STD4 and STD8 showed very little of it was due to melting, although melting may initiate FO>100 °C (s)a 152 102 104 106 the subsequent foil loss. A second mechanism to initiate foil Note: Average temperatures were calculated for the time FO remained loss appears to be delamination of the foil from the glass above 100 °C. See Table 2 for shelter codes. cloth followed by tearing due to air turbulence and (or) ob- aNumber of seconds that FO exceeded 100 °C. jects hitting and rupturing the foil and subsequent thermal degradation of the exposed glass cloth. What we observed toxic smoke, as opposed to the air temperatures in the brea- on shelters STD4 and STD8 was small pieces of foil tearing thing zone. The SKM shelter had minimal damage, so may off along a shear line. Outer temperatures peaked at 675 °C have been survivable. The SKMAL and STD shelters were for STD4 and 315 °C for STD8 temperatures likely not suf- non-survivable. Inconsistent setup protocols may have af- ficient to melt the foil (i.e., 660 °C). fected Roth’s results. An examination of the SS2KTI shelter showed it had split apart, since most of the glass thread had Conclusions melted on it as well as that on all the SS shelters. The SS This experiment showed liners lead to lower internal tem- shelters were also held together by the mechanical bonding peratures and aluminized liners yield even lower tempera- action of the needle during the sewing operation (i.e., the tures. One failure mechanism at this site was thread melting needle pushed shards of foil of one layer of SS into the next leading to seam rupture and a second was thermal degrada- layer which helped hold together all past SS shelters). The tion of Kapton™ films. The only commonly available mate- SS2KTI shelter seam failure was likely due to the thicker rials with higher degradation temperatures that can be linings preventing the needle puncture edges from mush- aluminized are glass cloth or metal foils such as SS. The rooming through the next SS foil layer. The SKM3 outside data from shelters deployed outside the plot showed decreas- the plot sustained more damage than the SKM inside the ing temperatures and less shelter damage as the distance plot. The FO temperature for shelter SS closest to SKM in- from the plot increased. The data suggest that increases in side the plot was 730 °C compared with 915 °C for STD2 distance from fuels as little as 4 m can make the difference closest to SKM3 outside the plot. In addition, SKM3 was between survival and non-survival. This conclusion is con- caught in the ground fires outside the plot. founded by both the ground fire effects and by the character- The data from the four STD shelters in the survival zone istic of the flames exiting the plot at a discrete location. experiment were confounded by ground fires igniting out- These results support the directive for firefighters to place side the plot. The data for peak and average temperatures is shelters in areas with the least expected flame contact and summarized in Table 12 and Fig. 5. There is a trend for tem- ground fuels. peratures to decrease as distance from the plot’s edge increases. The data showed temperature peaks first for the Plot 7: 5 July 1998 flames coming out of the plot (initial peaks) and 10–22 s Plot 7 was 150 m × 150 m and was burned with a south- later for a second set of peaks from ground flames. Table 13 east wind of 17 km·h–1. A SS and a SSHAL shelter were set shows only the initial peaks, which occurred approximately up inside the plot about 40 m from the plot’s northwest, 3 s apart, for the four shelters. The higher values for STD4 downwind edge and 38 m from the plot’s northeast edge. may be due to flames coming further out from the plot’s The main purpose of this experiment was to see whether edge at that location. The low FI value for STD6 indicates there was less conductive heat damage to a liner if it hung the thermocouple was not in contact with the inside surface, 3 cm below the SS ridgeline attached to higher temperature since it matches the trends for the two air temperatures. Sig- glass webbing. In addition, the bottom edges of the liner nificant flaming occurred above the forest canopy. Shelters were attached 3 cm away from the SS side–floor seams. Be- further from the plot edge would have been exposed to radi- cause of the hanging liner, this shelter was designated ant heating from those flames, while shelters closer to the SSHAL. Ackerman (1999) and Dakin set up STD shelters at plot were effectively shielded from the radiant energy by the 5 and 7 m outside the plot’s northwest edge. Roth set up 3 trees. We believe that values are higher for STD8 because of STDs and one SKM on a road on the northeast side of the its longer exposure to radiant heating. FO reached 100 °C at plot close to the north plot corner. 24, 25, 27, and 32 s for STD8, STD6, STD4, and STD2, respectively. Video imagery of the experiment indicates that Results damage to the shelters was due to ground fires that occurred The SSHAL split open because of thread melting, which after the fire had exited the plot. The severe damage to allowed the liner to come into direct flame contact. On the

Fig. 5. Survival zone peak temperatures as a function of distance Table 13. Plot 8 initial peak temperatures (°C) for four survival from the plot’s edge for four STD shelters (1998, Plot 8). zone shelters. STD2 STD4 STD6 STD8 FO 435 530 405 315 FI 335 140 95 165 SO 240 230 240 220 SI 215 180 130 235 30-cm peak 125 170 85 115 5-cm peak 60 100 80 105 Note: See Table 2 for shelter codes.

cause of the high internal temperatures. None of the shelters deployed by Roth on a service road were damaged. Video footage showed this area received no flame contact and only moderate radiant heat of 5–15 kW·m–2 (Ackerman 1999). All shelters in this location were survivable since they received no visible thermal damage. The two shelters set up by Ackerman and Dakin received heat flux up to 30 kW·m–2 (Ackerman 1999) and may have had brief flame contact. These shelters did not receive any external damage and thus were survivable.

Analysis Table 15 compares data from the two shelters inside the plot. The SSHAL generally exhibited lower peak temperatures than the SS shelter next to it. The SSHAL temperatures peaked 12 s after the flames arrived compared with a corre- Fig. 6. Time to breathe hot air for four survival shelters as a sponding 2-s delay for the SS shelter, suggesting a liner function of distance from the plot’s edge (1998, Plot 8). effect. Contrary to our expectations, SSHAL had higher temperatures than SS + STD (from plot 6). In addition SS + STD had a 34-s time delay between the rise of the FO sensor and the interior air 5-cm sensor, while the SSHAL data showed a 12-s delay. The higher temperatures observed in the SSHAL cannot be attributed to the shelter splitting open, as this did not occur until after the flames had passed.

Conclusions Because of the shelters failing and tearing open, the value of hanging liners could not be accurately assessed. Future SS shelters must be stapled, welded or sewn with SS thread or higher temperature quartz thread.

Overall conclusions These experiments have shown that stainless steel shelters withstand the severe heating without significant foil damage and that they are self-standing in turbulence. The seam failure problem is easily remedied with staples, higher temperature thread, or by welding layers together. The main drawbacks are poor reflectivity, brittleness and higher rates of heat transfer. For this reason, lined shelters were tested using a variety of liner materials in a number of layers. At this time, the only liner materials that have been successful are aluminum foil and S, E, and Q types of glass cloth. outside, both shelters were again uniformly gray indicating Liners tested in SS shelters characteristically disintegrated hotter temperatures than on Plot 8. The outside shell peak owing to heat conduction at the SS–liner seams. The SSHAL temperatures were 780–825 °C. The liner inside SSHAL was used a hanging liner to minimize this seam conduction and mostly melted but generally still connected to the side–floor is a lighter weight solution compared with multiple liner seam. The vegetation in the “ground prints” under both shel- shelters. While structurally stronger, SS shelters did not ters was mostly charred. Neither shelter was survivable be- show sufficient thermal protection to warrant operational use

Table 14. Plot 8: number of seconds (s) that air temperatures ex- Table 15. Plot 7 peak and average tempera- ceeded 200 °C and 100 °C and FO was above 100 °C for four tures (°C) for a lined and unlined SS shelter. survival zone shelters. SS SSHAL STD2 STD4 STD6 STD8 FO 800 780 30-cm above 200 °C 29 7 0 0 FI 750 760 5-cm above 200 °C 24 0 0 0 SO 805 825 30-cm above 100 °C 98 88 71 64 SI 840 705 5-cm above 100 °C 98 98 81 82 30-cm peak 805 805 5-cm peak 770 655 Time FO>100 °C 152 102 104 106 30-cm average 226 262 Note: See Table 2 for shelter codes. 5-cm average 260 242 Time FO>100 °C (s)a 231 204 by firefighters. Roth has tested shelters similar in design to Note: Average temperature values were calculated the USFS 1960s and 1980s models using multiple glass and for the time FO remained above 100 °C. See Table aluminum layers. Whereas the USFS only made a few proto- 2 for shelter codes. types, Roth is credited for the first extensive testing of these aNumber of seconds that FO exceeded 100 °C. models. His designs exhibit greater thermal resistance than SS shelters but have their own drawbacks: as shelters get smaller there is less trapped air to breath with possible when flame contact exceeds 5–10 s in duration. Even when higher humidity because of occupant perspiration and respi- shelters totally fail outside the plot, thermal damage to the ration. Since operational shelters have no frames, they may clothing under them suggests that a person wearing it may sag and allow conductive heat transfer to the firefighter. The have lived. This is consistent with current shelter training inside temperature sensors on Roth’s shelters were mounted suggesting that firefighters stay under the shelters no matter in the areas of maximal fabric draping, hence lower temper- how hot it gets and to keep their face and nose to the ground atures were reported that may not represent potential contact to protect their airway and ensure that they are breathing the temperatures. All models proposed for actual use should be coolest air. As demonstrated by marginal performance by tested with full-sized mannequins inside and no frames to STD shelters at the edge of the plots, any design modifica- better represent actual deployment conditions. The manne- tions that would improve the STD shelter could have big quins would displace more air and could record contact tem- benefits. The obvious suggestions based on the Northwest peratures. Data indicated that the STD shelters fail primarily Territories results are a better adhesive, effective quilting, by melting inside the plots and by partial melting and dela- use of S-glass, and finally thin E or S glass liners. This mination, with subsequent tearing in the flame front turbu- could shift marginal survivals to definite survivals, including lence. Silicone adhesives would increase delamination fewer burn injuries. temperatures from 260 to 340 °C but tend to off-gas meth- These studies suggest minimum survival zone size is de- ane. Alternatives may be a pin-holed outer aluminum foil pendent upon fuels, wind speed, and channeling, slope, shel- and a solid inner foil so that gases released during the ther- ter materials, and shelter design. Adoption of common mal degradation of adhesives would off-gas through the protocols will allow future researchers working with flames, holes. Data indicated that even with the foil gone the glass shelters and PPE to share data and pool observations into a cloth keeps out more heat than if the shelter totally breaks common database. This research, prior research, and later re- open. S-glass is not as tear-resistant but boosts temperature search has led to the development of a more flame-resistant resistance from 845 °C to 1055 °C, which would be a valu- shelter (Anderson and Petrilli 2003). able improvement in an entrapment where a STD shelter would begin to fail. A similar Quartz cloth shelter would Recommendations boost the temperature of the glass to over 1600 °C at a cost Recommendations for future studies would include of US$400–US$500 per full-sized shelter. The S-glass shel- (i) placing a camera within 2–3 m of a STD shelter to better ter would weigh the same as the STD shelter. Shelters man- identify the exact shelter failure mechanisms (i.e., melting, ufactured in the late 1960s had chemically treated paper delamination and tearing); (ii) recording sound inside and liners that improved shelter heat resistance but were re- outside shelters; (iii) recording video under shelters; moved because of lower thermal stability and toxicity con- (iv) measuring air humidity, oxygen, and smoke levels under cerns. A second improvement would be to add a liner made shelters; (v) looking for ignition of smoke (observed first in out of a lighter-weight E or S glass cloth. A suitable material laboratory tests); (vi) considering tri-laminates and pinholes would be 0.008 mm aluminum foil bonded to a light weight in the outer foil to mitigate gas ignition under shelters; (vii) glass cloth. This liner would ensure better protection in all collecting, at the very least, oxygen and carbon monoxide but complete flame immersion. Such a lined shelter would gas samples inside and outside different shelters within the have about 30% greater weight and bulk. Data from Plot 8 burn plot to determine whether direct flame shelters are sur- suggest STD shelters would suffer much less damage if the vivable from a toxicity standpoint; (viii) using 0.26 mm tearing of the delaminated foil could be reduced or stopped thermocouples for surface measurements as they are more with better adhesives or quilting layers together. durable than 0.13 mm thermocouples; (ix) constructing The survival zone experiments show that STD shelters quilted STD shelters from the best prototypes after compar- work very well under high radiant heat environments but fail ing different stitch types and stitch densities both with and

© 2004 NRC Canada Putnam and Butler 1615 without glass tape in the quilting; and (x) testing all shelters Butler, B.W., Bartlette, R.A., Bradshaw, L.S., Cohen, J.D., Andrews, being considered for firefighter use with the ground flaps P.L., Putnam, T., and Mangan, R.J. 1998. Fire behavior associ- held down with gaps along the edges and with no frames to ated with the south canyon fire on storm king mountain, Colo- more closely reflect actual use conditions. Tests should be rado. USDA, Rocky Mountain Research Station, Ogden, Utah. performed under a variety of fuel and fire conditions. Butler, B.W., Cohen, J., Latham, D.J., Schuette, R.D., Sopko, P., Shannon, K.S., Jimenez, D., and Bradshaw, L.S. 2004. Measure- ments of radiant emissive power and temperatures in crown Acknowledgements fires. Can. J. For. Res. 34. This issue. A study of this magnitude can only be accomplished Callin, G.D. 1969. Human tolerance to intense convective heat. through the concerted efforts of many individuals and orga- Aerospace Medical Research Laboratory, Wright–Patterson Air Force Base, Ohio. nizations. The authors especially thank the Canadian Forest Cohen, J.D. 2004. Relating flame radiation to home ignition using Service, the Government of the Northwest Territories and modeling and experimental crown fires. Can. J. For. Res. 34: the citizens of the community of Fort Providence for their This issue. enduring patience and support. We also thank Leslie Anderson, Kautz, J. 1997. Insulated boxes for protecting video cameras. In Tony Petrilli, Mark Wiggins, Dave Gasvoda, Lynn Weger, Surviving fire entrapments. USDA For. Serv. Rep. 9751–2817- Mike Vanderpas, Mark Linane, Dick Mangan, Paul Sopko, MTDC, Missoula, Mont. pp. 39–40. Bob Schuette, Kyle Shannon, Dan Jimenez, MaryAnn NFPA. 1993. NFPA–1977: protective clothing and equipment for Davies, and Jim Reardon from the USFS; and Tony Pastro wildland fire fighting, 1993 edition. National Fire Protection As- and John McColgan from BLM, who were all part of the re- sociation, Quincy, Mass. search effort. Special thanks go to Jim Roth, Mark Putnam, T. 1995. Your fire shelter. National Interagency Fire Cen- Ackerman, and Gary Dakin, for sharing data and analysis ter: NWCG PMS 409-2, Boise, Idaho. from their experiments. Finally, special thanks goes to Jim Putnam, T. 1996. Your fire shelter: beyond the basics. National In- Kautz for developing and operating cameras suitable for vid- teragency Fire Center: NWCG PMS 409-1. Boise, Idaho. eotaping under live fire conditions. SFPE. 1995. The SFPE handbook of fire protection engineering. Second edition. National Fire Protection Association, Quincy, References Mass. Shaddix, C.R. 1998. Practical aspects of correcting thermocouple Ackerman, M.Y. 1999. International crown fire modeling experi- measurements for radiation loss. In Proceedings of the 1998 fall ment: safety zones for wildland fire fighters. Department of Me- meeting of the Western States Section of the The Combustion chanical Engineering, University of Alberta, Department Report Institute, Oct. 26–27, University of Washington, Seattle, Wash. 103, Edmonton, Alta. The Combustion Institute, Pittsburgh, Pa. pp. 1–17. Anderson, L. 2003. The development and implementation of an Stocks, B.J., Alexander, M.E., Wotton, B.M., Stefner, C.N., improved fire shelter for wildland firefighters. In Proceedings of Flannigan, M.D., Taylor, S.W. et al. 2004. Crown fire behaviour the 3rd International Wildland Fire Conference and Exhibition, in a northern jack pine – black spruce forest. Can. J. For. Res. 3–6 Oct. 2003, Sydney, NSW, Australia. pp. 1–10. 34. This issue. Anderson, L., and Petrilli, T. 2003. New generation fire shelter de- Tonto National Forest. 1990. Accident investigation report: dude veloped for wildland firefighters. USDA For. Serv. Rep. 0351– fire incident multiple firefighter fatality. USDA For. Serv. SW 2313-MTDC, Missoula, Mont. Region, Payson, Ariz. Butler, B.W., and Putnam T. 2001. Fire shelter performance in sim- Veghte, J.H. 1986, Design criteria for fire fighters protective cloth- ulated wildfires: an exploratory study. Int. J. Wildland Fire, 10: ing. Second edition. Biotherm Inc., Dayton, Ohio. 29–44. Veghte, J.H. 1985. Evaluation for possible burn injury during ejec- Butler, B.W., and Cohen, J.D. 1998. Firefighter safety zones: a the- tion from T-46 aircraft. Biotherm. Inc., Dayton, Ohio. oretical model. Int. J. Wildland Fire, 8: 73–77.