VOLUME 15 NO.3 2008 Archival Products NEWS Fire and : A Soot Removal Technique Using Dry Ice Blasting By Randy Silverman

To say that for destruction ice Among U.S. Is also great And would suffice commercial —Robert 1 disaster firms, the current WELDER’S SPARK TOUCHED off the attic fire in the Sevier standard for ACounty Recorders Office in removing soot’s Richfield, Utah on May 2, 2006, igniting residue from a blaze that ripped through the crawl space books is to consuming the building’s paper-backed insu- Front of the Sevier County Recorders Office (Richfield, Utah, wipe down the lation. The fuel readily spent, the fire burned USA) on May 9, 2006, one week after the fire. Photo credit: itself out 15 minutes later, sparing the struc- Randy Silverman covers with a ture but coating everything below the rafters “chemical,” or with fine, powdery soot. The Problem This carbonaceous residue filtered down Among U.S. commercial disaster firms, the natural rubber through the ceiling tiles settling on everything current standard for removing soot’s residue sponge, and in the offices below including the historic from books is to wipe down the covers with a then “ozonate” 2 courthouse record books stored horizontally “chemical,” or natural rubber sponge, and then the books to on metal rolling shelves within the vault. “ozonate” the books to eliminate the residual About 300 nineteenth and twentieth century smoky odor. This approach leaves much to be eliminate the full-leather spring-back stationers’ bindings, desired. While the sponge traps much of the residual smoky many covered in protective white canvas jackets, fine, carbon-laden particulate in its tan, rubbery odor. were untouched by the fire but impregnated surface, it also quickly fills with residue. Recovery with a layer of soot and reeked of smoke. workers must constantly rotate their sponges to F IRE AND I CE – continued

expose unused areas to the grime and discard oily foundation of partially consumed combus- Soot’s fine spent sponges as they are not readily cleaned. tion byproducts. The carbon within these tar powder coats The wiping process forces some of the fine, droplets is so fine that it is readily dispersed by every exposed dark soot particles back into the interstices the “pressure and buoyancy created by the heat of the material being cleaned, especially when of the fire” and aerodynamic conditions such as surface, pene- that surface is as porous as the open weave “stack effect, wind pressures, the building geom- trating even the of canvas book jackets. etry and its barriers (such as walls and floors), tiniest crevices Trapped soot becomes more intractable and ventilation practices.”5 Soot’s fine powder and crannies, with time as the polymerized and dehydroge- coats every exposed surface, penetrating even nized byproducts of the fire chemically bond the tiniest crevices and crannies, anchoring the anchoring the to their surroundings.3 The friction of wiping carbon with oily tars where it lands. Removal carbon with also causes some portion of the sponge’s soft attempts by wiping, even with an absorbent, oily tars where rubber to transfer to the book’s surface, trading fleshy material such as a natural rubber sponge, one unstable residue for another.4 Finally, smears whatever soot does not bond to the it lands. exposing “cleaned” books to ozone to reduce sponge, compressing and embedding the the residual smoke odor causes further degra- diminutive, greasy specks further into the sur- dation. A strong oxidizer, ozone aggressively face and making them more difficult to remove. breaks down paper, cloth, leather and adhesives As soot ages, it chemically cross-links to the while it decomposes the organic components material it is in contact with, making immediate of the smoke—a highly undesirable tradeoff for cleanup the optimal course of choice. books of historic significance mandated by law Vacuuming with a HEPA filter in tandem to be maintained in perpetuity. with manual wiping can help, but alone it is In short, soot is an extremely tenacious mate- actually less effective than wiping with an rial to remove. Unlike dust, it is a solid/liquid absorbent material. In the 1997 Saskatchewan residue composed of carbon suspended in an Museum fire, Spafford-Ricci and Graham report the soot removal protocol used for book cleaning included an initial vacuuming of the book’s binding, followed by a separate vacuuming of the text block. Care was taken not to touch the surface of the books with the vacuum’s nozzle as this contact would push soot into the woven fabric of the bookbindings. After vacuuming, the second phase of this cleanup included mechanically wiping the book’s surface with rubber sponges or Webril® Wipes (a nonwoven 100% cotton pad used in the printing industry for non-abrasive cleaning of printing plates).6 Eliminating residual smoke odor from objects following soot removal is the next problem. In addition to spraying scents to mask the odor, three approaches predominate within the fire recovery industry: chemical deodorizing, thermal deodorizing and ozone treatment. Unfortunately, all have serious An interior office with evidence of smoke damage on the drawbacks when dealing with cultural her- walls. Photo credit: Randy Silverman itage material.

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Chemical deodorizing eliminates odors through a chemical reaction occurring when the chemical fumes of the product come into contact with smoke residue.

Record book storage vault with metal roller shelving; a temporary positive air ventilation system is set up to help with soot extraction. Photo credit: Randy Silverman Chemical deodorizing eliminates odors printing, paint, food, sewage and waste treat- through a chemical reaction occurring when ment, application of this technology to reduce the chemical fumes of the product come into smoke odors from heritage materials has not contact with smoke residue. These deodorizers yet, to my knowledge, been attempted. come in a wide range of extremely pungent Finally, ozone is commonly used to treat fragrances designed to “purify” air spaces rang- smoke odors in affected household and office ing in size from 1,000-20,000 cubic feet. The objects. This treatment includes creating long-term effects on cultural property of these copious amounts of O3 with an electric proprietary formulations have not been analyzed. ozone generator and sequestering the smoke- More broadly, however, harmful effects from damaged material in a confined space with gaseous pollutants—particularly sulphur the gas. Unfortunately, while O3 eliminates dioxide (SO2), oxides of nitrogen (NOX) and smoke odors, in high concentrations O3 9 ozone (O3)—have been well documented with is both harmful to human health and an paper, leather, textiles, dyes, pigments, inks, aggressive oxidizer known to harm a wide adhesives and photographic film.7 Introduction range of cultural heritage materials, as noted of gaseous chemicals for deodorizing purposes above.10 Hence, despite its common use for is not recommended until their long-term less significant objects, O3 should be avoided. effects can be tested. At present, the only safe approach to Thermal oxidation deodorizing is a second remove smoke odors from cultural material is approach used to eliminate volatile organic to isolate objects in a room with an operating compounds (VOCs) from the ambient air. air purification system containing activated Essentially, the system is an afterburner that carbon, zeolite and/or potassium perman- draws workplace air through a combustion ganate filtration. Continuously re-circulating chamber where VOCs are incinerated.8 filtered air past the objects will gradually Mostly used in industrial settings to deal reduce smoke’s lingering odor if the material with gaseous byproducts from petrochemicals, can be well exposed to the air flow. An inex-

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pensive alternative is to place small amounts of including dispatching paint from decorative In the aftermath material in relatively airtight enclosures (such metalwork; cleaning dirt from brick, granite, of the Sevier as a large, sealed plastic garbage bag) in close marble, onyx or other stone materials; stripping County Recorders proximity to large quantities of exposed baking built-up wet or dry ink from printing presses; Office fire, a soda. Either approach may take two to three removing fused dust from electrical turbines, months to work with the key being to expose generator windings and transformers; and non-damaging the impacted material to the absorbent media. remediating mold from building interiors.13 alternative to the Michael Trinkley reports, “Records which sur- The system is portable and can be powered current cleaning vived the 1906 San Francisco fire and are today by an electric generator, adding significantly in the National Archives still smell strongly of to its merits since the County Recorder would options seemed smoke—over 90 years later,”11 a condition not permit the damaged books to leave the desirable. possibly exacerbated by the lack of air exchange. Recorders Office. The process works by shaving solid blocks

Sevier County of dry ice (frozen CO2) into granules ranging in In the aftermath of the Sevier County Recorders size from the diameter of sugar to the shape of Office fire, a non-damaging alternative to the rice, depending upon the application. These current cleaning options seemed desirable. granules are propelled in a compressed air Invited by the responsible commercial recovery stream of 30-300 PSI against the surface company to serve as a consultant,12 I suggested to be cleaned. Dry ice blasting is considered dry ice blasting as an interesting possibility. Dry completely non-abrasive when used on surfaces

ice blasting has proven its utility in a variety of harder than frozen CO2, but can be used to industrial applications over the past decade “antique” wooden siding by differentially abrading the softer, pithy wood and leaving

the grain. Frozen CO2 pellets emerge from the nozzle at -78°C, dramatically lowering the surface temperature of the media being cleaned and causing incremental shrinkage. This contraction occurs simultaneously as the

CO2 sublimates to its gas phase, expanding approximately 80-800 times its original size. These multiple forces—contraction due to cold, turbulence caused by rapid sublimation and pressure from the compressed air stream— occur simultaneously. As the minute dry ice particles penetrate the interstices of the media

being cleaned, the CO2 sublimates leaving only “dirt” as the residual byproduct. In preparation to attempting soot removal from Sevier County’s record books using dry ice blasting, a couple of expendable modern publishers’ bindings were tested. With the dry ground sugar-fine, the PSI set First test sample; a late twentieth century publishers’ bind- to a minimum (30 PSI) and the compressed ing. Dry ice blasting adequately cleaned surface grime but air nozzle held far enough from the books to if the focus of the blast was prolonged, gold stamping and pigment from the publishers’ cloth were removed. prevent abrasion (15-18 inches), a local appli- Photo credit: Randy Silverman cator14 expertly cleaned these mock ups while

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We then compared dry ice blasting with two other forms of soot removal using actual record books; wiping down part of a book with a natural rubber Second test sample; cleaning results from a lightly soot An 18th century full-leather record book sitting on the damaged 20th century record book covered in a protective Alpheus Precision SeriesTM Model T-2 dry ice blasting sponge and white canvas jacket. The area of the jacket left of the machine as it is refilled with block dry ice. Photo credit: vacuuming number “73” and below the word “Deed” was wiped Randy Silverman with a natural rubber sponge; right of the number “73” and another section below the word “Deed” was vacuumed with a HEPA vac; record books; wiping down part of a book and, the area above the words “Deed Record” was dry ice with a blasted. Photo credit: Randy Silverman with a natural rubber sponge and vacuuming another section with a HEPA filter. The HEPA filter. I monitored the effect. The applicator played rubber sponge proved reasonably effective 15 the machine’s spray of CO2 granules in a although it left some visible soot residue. The steady sweep across the bindings, his experience HEPA-vacuuming proved far less effective essential to preventing damage. The technique than the sponge, underscoring the bonding worked flawlessly, but we discovered that too strength of the soot, even a week after the long a focus on one spot or allowing too little fire. Dry ice blasting proved the most effec- distance between the nozzle and book’s surface, tive of the three methods and caused no could remove dye from the cloth or gold foil detectable abrasion. In addition to removing stamping from the cover. We also found that older, hand tooling (both hand stamping and rozen CO2, which comes from liquid CO2, used decorative lines run with a roll) presented no Fin soot removal is different than CO2, which is produced as a by-product of another process. It is problem in the cleaning, suggesting that mod- not excess CO2 but CO2 that has been reclaimed or ern titling on mass market books is far more recycled from CO2 already existing in the environment. friable than earlier handwork. Similarly, direct- Dry ice blasting, an environmentally conscious way to ing the dry ice nozzle directly at the edges of use existing CO2 to our advantage, is environmentally friendly and not environmentally damaging. the text could abrade the paper surface slightly, so the situation was remedied by focusing the Dry ice blasting pellets is environmentally friendly nozzle’s aim specifically at the board edge so and contains no secondary contaminants such as solvents or grit media. They are non-toxic, non- only the peripheral dry ice spray played over hazardous creating advantages to the environment, the fore-edge, head and tail. By firmly clamping your employees, and production facility: the text closed and minimizing direct pressure • No secondary waste to the paper edges the text was undamaged by • Safe for the environment the cleaning process. • Safe for employees We then compared dry ice blasting with • Safe for end products • Safe for equipment two other forms of soot removal using actual

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to remove the deodorizers from the boxes, While dry ice claiming she actually preferred the smell of blasting has smoke to the noxious deodorant! She also been successfully believed the smoke odor was rapidly dissi- used for mold pating as the books aired out. As with any new conservation technique, remediation dry ice blasting will surely prove to have its limi- on building tations. Based on the excellent results at Sevier surfaces, its County, however, it appears the technique has great promise for addressing certain problems application to and should be considered as a viable option removing mold as the situation demands. Additionally, further from damaged safeguards or modifications to the approach bindings has described herein may be warranted. Great care should be exercised, for example, when testing yet to be dry ice blasting’s effectiveness for removing soot investigated. from rare books, as the age and variability of the material involved might well present numerous challenges. While dry ice blasting has been successfully used for mold remedia- Randell Heath, President, CO LDSWEEP Dry Ice Blasting, 2 tion on building surfaces, its application to at work removing soot from a Sevier County record book. Photo credit: Randy Silverman removing mold from damaged bindings has yet to be investigated. Dry ice blasting seems the soot, the cleaning eliminated years of to offer much promise and additional reports embedded hand grease as well as a piece of and testing arising from future applications pressure sensitive tape along with the discolored of the technology are encouraged. adhesive residue beneath it. As a further test, each cleaned object was sequestered overnight Notes 1. Frost, Robert, “Fire and Ice,” Collected Poems, Prose, in a sealed box to determine how much residual and Plays (New York: Library of America, 1995): 204. smoke odor remained. Again, dry ice blasting surpassed the other cleaning methods. 2. The principle source for natural rubber sponges (stock #60142) is: Quality Rubber Co, 415 Metallic Lane, Sedalia, The technique also proved to be far faster MO 65301. Tel. 660-826-4641; toll free, 800 597-9947. than wiping down the books with rubber 3. On the long-term problems of soot removal from sponges. The canvas-covered bindings took cultural property, see: Roberts, Barbara, et al. “An longer to clean than books with exposed Account of the Conservation and Preservation Procedures leather, but on average, six books were dry Following a Fire at the Huntington Library and Art Gallery,” Journal of the American Institute for Conservation 27:1 ice blasted per hour (50 hours total). Jayrene (Spring 1988): 1-31; Spafford-Ricci, Sarah, and Fiona Nielsen, the County Clerk, expressed her Graham, “The Fire at the Royal Saskatchewan Museum, amazement at the end result. She claimed Part 1: Salvage, Initial Response, and the Implications for Disaster Planning,” Journal of the American Institute the books had never looked so clean. While for Conservation 39, no 1 (Spring, 2000): 15-35, and, building repairs progressed, the commercial Spafford-Ricci, Sarah, and Fiona Graham, “The Fire at the Royal Saskatchewan Museum, Part 2: Removal recovery company, leery of a slight residual of Soot from Artifacts and Recovery of the Building,” smoke odor, packaged the cleaned volumes Journal of the American Institute for Conservation 39, for storage in boxes containing a chemical no 1 (Spring, 2000): 36-56. deodorizer. In direct discussion about this 4. See: E. Moffatt, “Analysis of ‘Chemical Sponges’ Used with the County Clerk, Ms. Nielsen agreed by the Commercial Fire Cleanup Industry to Remove Soot

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Before and after, “Chattel Mortgagors Index B, Sevier County, Utah” the bottom half of the book cleaned by dry ice blasting, the top half still covered in soot. Photo credit: Randell Heath. from Various Surfaces,” IIC-CG (International Institute for Whitmore, and Cynthia L. Whittman. Protection of Works Conservation—Canadian Group) 17/3 (1991): 9-10. of Art From Atmospheric Ozone, (Los Angeles: The Getty Conservation Institute, 1989). Full text available at: 5. McKinnon, Gordon P. and Keith Tower (eds.), Fire www.getty.edu/conservation/publications/pdf_publications/ Protection Handbook, 14th ed. (Boston: National Fire alpha_author.html; Salvin, V. S., “Ozone Fading of Dyes,” Protection Association, 1976): 2-19; 2-27. Textile Chemist and Colorist 1 (1969): 245-251. Shaver, C. L., Glen R. Cass, and James R. Druzik, “Ozone and the Deteri- 6. Spafford-Ricci, Sarah, and Fiona Graham, “The Fire at oration of Works of Art,” Environmental Science & Tech- the Royal Saskatchewan Museum, Part 2”: 48-49. nology 17 (1983): 748-752.

7. Committee on Preservation of Historical Records, 11. [Trinkley, Michael], Chicora Foundation, “Fire” [ca. National Materials Advisory Board, Preservation of June 16, 2003], recovered from the World Wide Web 24 Historical Records (Washington, D.C.: National Academy May 2006: www.chicora.org/fire.htm. Press, 1986): 11-31; Baer, Norbert S., and Paul Banks, “Indoor Air Pollution: Effects on Cultural and Historic 12. Utah Disaster Kleenup (13081 South Minuteman Materials,” International Journal of Museum Manage- Drive, Draper, Utah 84020 USA; tel. (801) 553-1010; ment Curatorship 4 (1985): 9-20. www.utdk.com/index.php is the commercial firm responsible for this recovery. 8. Thermal Oxidation Deodorizing Machine, by Osaka Gas Engineering Co., LTD, recovered from the World Wide 13. CO2LDSWEEP Dry Ice Blasting, brochure (n.p; n.d, Web 25 May 2006: remediation on building surfaces, its c. 2006). application to removing mold from damaged bindings has yet to be investigated. Again, dry ice blasting seems to 14. This experimental work was conducted by Randell offer much promise, and additional reports and testing Heath, President, CO2LDSWEEP Dry Ice Blasting (3612 arising from future applications of the technology are Quail Point Road, Mountain Green, UT 84050 USA; encouraged. tel. 801-876-5432; [email protected]). Mr. Heath is a certified mechanical engineer, and coincidentally, was 9. U.S. Environmental Protection Agency, “Ozone Gener- originally born in Sevier County, UT. He served as a ators that are Sold as Air Cleaners: An Assessment of subcontractor to Utah Disaster Kleenup at the rate Effectiveness and Health Consequences,” recovered of $150.00 per hour. from the World Wide Web 25 May 2006: www.epa.gov/iaq/ pubs/ozonegen.html; U.S. Environmental Protection 15. The dry ice blasting machine used was the Alpheus Agency, Air quality criteria for ozone and other photo- Precision Series TM Model T-2. This machine is quite chemical oxidants, EPA-600/8-78-004 (Research Triangle mobile, measuring 14 x 22 x 20 inches. (35.56 x 55.88 x Park, North Carolina: U.S. Environmental Protection 50.80 cm.; W x L x H) and weighing 110 lbs. It stores 12 Agency, 1978). lbs. of block dry ice and produces a blast pressure range of 30-120 psi. 10. Bogarty, H., K. S. Campbell, and W. D. Appel, “The Oxida- tion of Cellulose by Ozone in Small Concentrations,” Textile Randy Silverman is Preservation Librarian at the University Research Journal 22 (1952): 81-83; Cass, Glen R., James R. of Utah Marriott Library. He may be reached at randy. Druzik, Daniel Grosjean, William W. Nazaroff, Paul M. [email protected].

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