Radon mitigation in schools
Case studies of radon mitigation systems installed by EPA in four Maryland schools are presented
By David Saum, A.B. Craig and Kelly Leovic
Editor's Note: Part 1 ofthis article (which Based on the information ob~ta;:i-;::n-;;::ed;:;--;::c:;;ae.se;;s;mp;'l!/l,..,,.,:
expansion joint. where two parts of the building were JOlned. The material 1n the expansion joint had disintegrated and the parts appeared to have separated, 10 le ·:«: :ng a 1-in. gap between the floor and ~ 1.,_ This gap was concealed by an (3 alu1·1inum angle iron installed when the E: c building was built. 0 -a When the return fan was operating, al initial tests in this room showed a large a: flow of radon-containing soil gas out of 5 this crack. The radon level was about 500 pCi/L in the soil gas entering the room through the crack, the same mea sured under the slab in the middle of s tr · '.)Om. l• When the return air fan was turned l! oir o.n d the room was pressurized by the ,· 10 air supply fan, room air flowed into the Differential Pressure Across the Slab and the Outside Walls crack and, consequently, no soil gas entered. The pressure in the room rela tive to the subslab increased to about O.D1 in. WC and radon levels in the room 0 quickly dropped below 2 pCi/L. The floor-to-wall crack was sealed 6 with backer rod and urethane caulking. 3: c Th ;'' sealing decreased radon levels only -10 in- c... sli ~ . illy when both fans were off, indi c 1th cating other soil gas entry points in the ne e. room. e Subslab a ::I -+ ' The influence of HVAC operation on Ill -20 IL. Ill the pressure differential between this !!! :ie- room and the subslab area and the re a. sulting radon levels in the room are dis on· played in Figure 1 for a seven-day period. -30 ing (The return air louvers were closed dur .ted ing these measurements.) While the I and H\'/., '.:; system is operating, the room is ~ at ,, higher pressure than the subslab -40 esh area and, consequently, radon entry is fhis reduced. However, when the HVAC sys 100 1 all tem is turned off during night and week· bal· end setback, pressure in the room be and comes negative relative to the subslab that area and radon levels increase. )res· 90 As a temporary solution to reduce I 1hen radon levels, the return air fan was left off I Outdoor re in and the HVAC system operated with only ii:' I I!- I \./ the air supply fan. Under these condi I 3.dOn !!! I tior.s, all rooms showed positive pressure ::I \ callY ~ 80 and had radon levels below 2 pCi/L dur I! I I I "\ .. we cu \I ing HVAC operation. The damaged c. I \ , I I \i '~ \ JSlab. supply fan has now been replaced and E \I doff. the air supply and air return systems are ~ \J \j Jsitive being balanced. ; than As a precaution to reduce radon en 70 idling I I try when the air handlers are not operat ~ ly tan ing during night or weekend setback, two signi· fan .assisted subslab depressurization 3 SUP' po-. .ts have been installed. It is antici· !SS ail pa :>.) d that this will be an effective miti :wing gation system since the school was con 221 226 man\ structed on 4 in. of subslab aggregate. 1988 Julian Day Follow-up testing was initiated during the .est ra· 1988-89 heating season and will con Figure 1. Influence of HVAC operation on pressure differential and radon level ~ preS' tinue in the entire school during the in Case Study A. to-w8 1989-90 healing season. N3S af ASHRAE JOURNAL February 1990 21 ry 19g; Radon mitigation
Case Study B intake into the return air duct is under measured with charcoal canisters over a weekend in May 1988 with the air han· This is a small school built on the negative pressure during fan operation. dlers off. Measurements ranged from 78 side of a hill with a walkout basement Pressure measurements indicate that the along the lower side. The unexcavated bullding is under positive pressure even to 82 pCi/l in the basement and from 18 area is slab-on-grade with the slab ex when the fresh air intake is set tor mini· to 33 pCi/L on the first floor. Subslab and block wall grab samples measured as tending over the basement area and mum supply. However. since the HVAC system is normally set to run only when high as 1.500 pCi/l. resting on steel bar joists. The foundation Continuous radon measurements walls are concrete block. The interior wall heating or cooling is required, the system were made on both floors the school of the basement supports the end of the may not operate during mild weather. In of bar joists and the slab. This wall is not addition, the temperature In the below· during all phases of mitigation. Before mitigation. radon levels rose dramatically painted or waterproofed on either side. grade part of the school is often buttered at night if the air handlers were off but did Building plans specify 4 in. of subslab and. consequently, the basement HVAC aggregate. system does not run as often as the up· not rise during co11tinuous operation. stairs system. Pressure measurements indicated that The HVAC system consists of a sin gle-fan system on each floor. A fresh air Radon levels in all rooms were operation of the air handlers produced a slight positive pressure in the building relative to the subslab area, thus reduc ing soil gas entry. In the hottest part of the summer, radon levels rose dramatically overnight when the air handlers were off. It is sus pected that a night stack effect resulted Basement since the hot inside daytime tempera Radon ~ tures did not decrease as rapidly at night as the outdoor temperature. ~ Overnight levels as high as 150 pCi/ 0 L were re ached in the basement, and S: c: levels as high as 100 pCi/l were reached 0 "C on the first floor when the air-handling a:nl fans were off during hot weather. Con· tinuous operation of the HVAC system 5o r-~~~--r1i--+-1-~~~~--1~~~~~~~~~~~--1.~--1 reduced radon levels to less than 4 pCi/L First Floor Aa.,aon- 1 within an hour. I I First Floor Radon As a temporary solution, the HVAC I system was run continuously while the school was occupied. For a permanent solution, subslab depressurization points were installed in phases in both the base ment and on the first floor. O_ue to the high radon levels and complex foundation, lt was anticipated that several suction points would be needed. A 1-ft·diameter subslab suction pit was installed in the basement with a 4-in. diameter pipe. Radon reduction was 0 about 50 percent, with the subslab pres sure field extending less than 30 ft. The g suction pit was excavated to a diameter of .5 about 3 ft, with an additional decrease in ,.... radon levels and an increase in pressure 0 0 -10 field extension. The suction fan was re e. placed with a larger fan, resulting in addi ! :i" tional reduciions in radon levels. This also increased pressure field extension to 40 !!"' Q. ft. This basement suction point also -20 caused some measurable depressuriza tion under the first floor slab, indicating some air flow between the slabs. To evaluate the effectiveness of the single-point subslab suction system in this school and to investigate the effects the single-fan HVAC system on mitiga· 155 160 ~f t1on performance, Figure 2 shows radon 1988 Julian Day and pressure measurements in the school over a 10-day period in June Figure 2. Radon and pressure measurements over a 10-day period in Case 1988. Study B. i The first-floor single-fan HVAC sys tem was operated continuously durinq
22 ASHRAE JOURNAL February 1990 the school week to reduce radon levels 4 pCi/L on both floors. except for occa with the exhaust fans and the subslab while the school was in session on the sional brier excursions at night. A larger depressurizalion systems operating, in first floor. Since the basement was un fan was Installed, and th is appears to be dicating that the subslab suction systems occupied during the monitoring period, reducing radon levels satisfactorily. More effectively overcame the negative pres the basement HVAC system was not than 10 pressure field extension mea sures caused by the exhaust tans. c:Jerated. surements made on the first floor showed New classroom wing. Weekend Over the weekend (day 156), the little short-term variation when the first charcoal canister measurements were HVAC system and the single-point sub floor HVAC system was turned off. This in made in April 1988 in this wing with the slab suction system on the first floor were dicates that the present system is achiev unit ventilators off. All but one room turned off, and the radon levels rose ing adequate coverage even when the measured above 4 pCi/L; a room in the quickly to more than 70 pCi/L on the first HVAC fan is not op erating. northeast corner measured 27 pCilL. floor and 140 pCi/L in the basement. Although subslab suction was effec Levels decreased from north to south in On day 157, the subslab suction ti ve in solv ng a serious radon problem at this wing, as did subslab radon levels. system remained off, but the first-floor this school, it was surprising that it took · A CRM was placed in the room with HVAC system was turned on. Radon eight suction points. Aggregate under the highest radon levels. When the unit levels on both floors dropped and the th e slab was confirmed visually at every ventilator was off, levels above 20 pCi/L '· ;erential pressure under the slab and suction point: however. the aggregate were reached nightly but remained be· '""'hin the block wall became slightly used was probably unscreened "crusher low 2 pCi/L when the unit ventilator was negative relative to the room. On days run,'' containing a great deal of fines. This run continuously. Pressure measure 158-163, both the HVAC system and sub tends to confirm the belief that screened, ments with a micromanometer confirmed slab suction system were operating and coarse aggregate (0.75to1 .25 in., essen that the unit ventilator was pressurizing radon levels remained low. tially free of any material less than 0.25 in. the room slightly. On days 164 and 165, the subslab diameter) is preferred for optimal opera Since the unit ventilators are off at suction system was operated and the tion of subslab depressurization systems. night (except in extremely cold weather first-floor HVAC system was off. This in when th ey are cycled) , it was decided Case StudyC creased first-floor radon levels to 40 pCi/ to install two subslab depressurization L. indicating that one suction point was This school building is slab-on points in the wing. These 4-in.·diameter : )t adequate if the HVAC system was not grade with block walls and no utilities suction pipes were installed in the hall operating. below grade except sanitary sewers. The and manifolded with an above-ceiling To ensure acceptable radon levels original building was constructed in 1956 6-in.·diameter pipe running to a fan at the on the first floor while the HVAC system and has four area air handlers for heating north end of th e building. One suction was not in operation, another suction and ventilating with a central boiler room. point was installed with a 3-ft-diameter point with a 3-ft-diameter suction pit was A classroom wing was added in 1968 suction pit about 20 ft from the east end installed on the first floor. Addition of this and unit ventilators are in each room . of the hall. The other suction point was in· suction point reduced levels on the first None of the building is air-conditioned. stalled with ·a 1-ft·diameter suction pit floor, although radon levels on both floors Construction plans specified 4 in. of about 40 ft west of the fi rst point. Pressure still rose above 10 pCi/L at night with the subslab aggregate under the entire field extension measurements indicated HVAC system off. building. that the two fields overlapped. and all of Pressure field extension measure Elevated radon levels were found in the wing was depressurlzed to the out· ments made with these two suction the locker rooms on each side of the side walls except for the southernmost points operating indicated incomplete gymnasium in the original building and in classrooms. coverage of both floors. Consequently, the new classroom wing. Mitigation of Since the pressure field extension two additional suction points with 1-ft each of these areas is discussed as around the 1-ft-diameter suction pit was diameter suction pits were installed in the follows. not as great as around the 3-ft-diameter basement. and a fifth suction point with a Original building locker room miti suction pit, the Ht-diameter suction Ht-diameter suction pit was installed on gation. Although the locker rooms and pit was increased to 3 ft in diameter. This the first floor. · gymnasium are on the same air handler, extended the measurable depressuri· Nine pressure field extension mea the gymnasium measured 2 pCi/L; th e zation area by 10 ft to the south (enough surements showed overlapping fields girls' locker room, 5 to 6 pCi/L; and the to reach the last two classrooms) and al· oetween suction points in the basement boys' locker room, 5 to 19 pCi/L. Further most doubled the amount of depressuri· area, indicating that all of the basement examination indicated that each locker zation in the test holes in all directions sub-slab was adequately depressurized. room area had large exhaust fans to re around the suction point. With the sub· Basement radon levels measured less move odors and shower steam. slab depressurization system operating than 2 pCi/L with the air handlers off and Differential pressure measurements and the unit ventilator fans off, radon the mitigation systems operating: how· {using a micromanometer) with the air levels were less than 4 pCi/L in all ever. first-floor radon levels still rose handler and exhaust fans operating cor classrooms. above 4 pCi/L at night with the air han related, with the radon levels showing dlers off. that the gymnasium was slightly positive, CaseStudyD Based on mapping of subslab radon the girls' locker room area slightly nega The original building of this school 1avels in more than 20 test holes on the tive, and the boys' locker room area sig· was built in 1958 and is heated with hot ·irst lloor, three·additional suction points nificantly negative. water radiant heat in the slab. In 1978, were installed, each with a 6-i n.-diameter Construction plans showed that a kindergarten room was added to the pipe and a Ht-diameter subslab suction each locker room area was a continuous original building and a separate building pit. Two points were manifolded to a sin slab over aggregate. As a result, a (referred to as Building B) was built. gle fan, and a separate fan was installed subslab suction point, using a 6-in. pipe, Building B contains four classrooms, a on the other suction point. was placed in each locker room area with library, a teachers' workroom, a confer ! After installation of these last three a 1-ft-diameter suction pit. Both locker ence room and restrooms. suction points, radon levels stayed below room areas measured less than 4 pCilL The kindergarten room is heated
ASHRAE JOURNAL February 1990 23 Radon mitigation with hot water radiant hea.t. and Building pipes) and Building B had 4 in. of ag was placed in one of the classrooms in 8 Is heated with unit ventilators. Office gregate under a 4-in. slab. Building B to measure the effects of unit space in the original building is air condi· All rooms in both buildings were ventilator operation on radon entry. It was tioned with a window unit. No other area tested with charcoal canisters over a found that radon levels would rise over of either building is air conditioned. weekend in mid-April 1988. The eight night to more than 20 pCi/L with the ven The original building has two 3,600 rooms in Building B measured between tilator off, but would remain below 2 pCi/L ctm roof-mounted fans that could be 17 and 20 pCi/L It is believed that the with the ventilators on. Again, this shows used to exhaust air in plenums over the unit ventilators were off during the test that this type of ventilator can pressurize hall ceiling. Each room has a ceiling vent ing weekend, but this could not be con the room slightly, preventing radon entry connecting to these hall plenums. How firmed. Seven tests in the classroom s, when run continuously. ever, the exhaust fans are never used, so library and multi-purpose room in the Since the ventilators are oH during the building has no active ventilation original building measured between 12 night setback, a four-point subslab de system . Plans showed that the original and 23 pCi/L. Mitigation of the two pressurization system was installed. Four building had 6 in. of aggregate under a buildings is discussed as follows. 4-in.-diameter pipes were connected to 6-in.·thick slab {contairnng hot water Building B (unit ventilators). A CRM two 6-ln.-diameter manifold pipes above the drop ceiling with a common suctlon fan. (Two vertical pipes are manifolded to each overhead pipe.) Pressure field ex tension measurements indicated that Radon in Room 112 ' depressurization extended 50 ft. the minimum distance necessary to reach all parts of the slab. With the subslab system operating and the unit ventilators off, all rooms re mained below 4 pCi/L. However, based on the pressure field extension measure· ments, the system may be marginal dur· Ing cold weather. If radon levels rise above 4 pCi/L, it is believed that subslab depressurization can be improved by sealing the floor-to-wall opening. Expan· sion joints (0.25 in. in width) around all of the slabs in the building are deteriorat ing, leaving significant openings to the subslab. This probably leads to some short-circuiting of the subslab depres surization system. Original building (intra-slab radiant heat). Subslab suction on this intra-slab radiant-heated building was a challenge since construction plans showed that the hot water pipes in the slab were 15 In. or less apart over the entire building. As a result. it was difficult to locate an area where a 6-in. subslab suction point could be placed without damaging a hot water pipe. A 3 sq ft area without water pipes was finally located in each room . A hole was successfully cut through one of these areas. The plans indicated that the aggre· gate was a minimum of 6 in. deep, much deeper than at any other school exam ined. A 6-in. 24 ASHRAE JOURNAL February 1990 The New ASHRAE concrete. It is believed that this layer of an effective, temporary solution to re Pocket Guide coarse stone made for a much greater duce elevated radon levels in schools, pressure field extension and will be depending on HVAC system design. The ASHRAE Pocket Guide for Air Con studied further. Preliminary follow-up Whether such a technique is a feasible tests indicate that this one suction point long-term solution depends on factors ditioning , Heating, Ventilation and will solve the radon problem in the such as the proper operation of the Refrigeration expands and updates the criginal building. system by maintenance personnel, var original Pocket Handbook with data To analyze the effectiveness cit a iations in outside environmental condi from the 1989 Fundamentals Handbook single-point subslab suction system and tions, and any additional maintenance and the revised ASHRAE Standard to investigate the pressures that control costs and energy penalties associated radon levels in schools during hot weath with increased operation of the HVAC 62-1989, Ventilation for Acceptable In er, radon, pressure and temperature system. door Air Quality It includes a new sec were monitored continuously in one 3. A subslab depressurlz;atlon sys· tion on "Owning and Operating ," new classroom , as shown in Figure 3. The tern can usually overcome negative pres· heat gain information, new data on pipe classrooms were kept closed during this sures ir:idueed by HVAC operation in sizing , plus much more. Bulk order dis period of very hot weather, and there is schools it there are no return air ducts no ventilation system in this building. under the slabs. As with houses, subslab counts and imprinting available. Contact When the subslab suction system depressurization is more successful (and Publication Sales for details. Phone: .vas turned off from days 222-225 (July requires fewer suction points) when the (404) 636-8400. Fax : (404) 321-5478 . 1988), the radon levels quickly rose and slab is poured over clean, coarse aggre followed a diurnal cycle that seems to gate. Code: 90041 1-P (inch-pound) match the temperature cycle. When the 4. Effective mitigation of schools us 90042 SI (metric) will be outdoor temperature was coolest relative ing subslab depressurization requires available 2190. to indoor temperature, the radon levels greater fan capacities and suction pipe were highest. This can be expected from diameters than does mitigation of houses. List: $18.00 the stack effect, as discussed in Case The capacities of the fans used in these Member: $12 .00 Study B. Although a small positive pres school installations were typically at least sure was measured across the slab dur 300 elm (at 0.75 in. WC) compared to 'ng this period, it does not show signifi capacities of about 150 cfm (at 0.75 in. cant diurnal variation. The differential WC) for fans commonly installed in house pressure across an outside classroom subslab depressurjzation systems. Suc wall does not show much correlation with tion pipe diameters of 4 to 6 in. often the radon levels, except for a sharp dip in proved successful in these installations, the middle of day 224 that may be due to compared to pipe diameters of 4 in. or wind. less typically used in houses. Kindergarten room. Since the kin dergarten room is an addition, the sub Acknowledgments slab area does not communicate with the The authors would like to thank all of original building. Consequently, a suc the school personnel who contributed to '. ion point was put in a closet adjacent the information presented in this paper. to a restroom where the hot water pipes were spaced 24 in. apart to clear the sewer line of the commode. This suction point lowered radon levels to less than 2 pCi/L. No pressure field extension mea surements were made for fear of damag This publication is ing a heating water pipe. available in microfonn Preliminary findings from UMI. The following preliminary conclu Please send me information about the titles sions can be drawn from the EPA's ex I've listed below:------perience in assisti ng in the installati on of radon mitigation systems in Maryland, Name______Virginia, Tennessee and North Carolina TlUe ______schools. These conclusions are based on limited studies and will be verified and Company/Institution ______expanded with further research. Address ______1. One of the most si gnificant factors City/State/Zip______contributing to elevated levels of radon in Phone (,------schools and influencing the mitigation approach ls the design and operation of U·M·I th e HVAC system. The complexities of A Bell & Howell Company large building HVAC systems present 300 North Zeeb Road , Ann Arbor, Ml 48106 USA problems not previously encountered in 800-521-0600 toll-free house mitigation. 313-761 -4700 collect from Alaska and Michigan 2. Pressure control through con 800-343-5299 toll-free from Canada tinuous HVAC fan operation can ofte n be ASHRAE JOURNAL February 1990 25