UNCLASSIFIED

AD 668 220

AN ANALYSIS OF ROOF WASHDOWN VERSUS APPLIEDSHIELDING AS A FALLOUT COUNTERMEASURE

Hong Lee

Stanford Research InstituteMenlo Park, California

December 1966

Proesed fcr...

DEFENSE DOCUMENTATION CENTERDEFENSE SUPPLY AGENCY

U. AvabTe MRCo _____SITO TO

U. B. DEPARTMoN OP CONmmE NATIONAL BUREAU OF STANDARDS I NSTITUTE FOR APPLIED TECH4NOLOGY

AN ANALYSIS OF ROOF WASHDOWNVEiZSUI-i APPLIED SHIELDINGAS A FALLOUT COUNTERMEASURE

CO)NTRACT ~KN0022266C0231D hc0CD WOR KLVf NO. 3231 C

ori doblcu~ h n ap MAY 1 1968dllstibu i, ~1~. and solie~ LP~ ij

Uni ioLL~ -j

-----~~K .

AN ANALYSIS OF ROOF WASHDOWNVERSUS APPLIED SHIELDINGAS A FALLOUT COUNTERMEASURE

By: HONG LEE

SR I Project No. MU -5806

CONTRACT NO. N0022866C0231OCP WORK UNIT NO 3231C

P~repared~ frr

OFFICE OF CIV'L DEFENSE

DEPARTMENT OF THE ARMYI

(C CHN ICA L. AAN A GF'AEN T 0 FF IC E

SAN FRANCISCO CALIFORNIA

This report has been reviewed in the Office of Civil Defense and approved for publication. Approvaldoes not signify that the contents necessarily reflect thie views anod policies of the Office of Civi I Ofense.

ABSTRACT

This stzwdy pro-vides guidance on the basic applicability and rels-tive worth of rrocf -;ashdown as a fallout radiation countermieasure. T~hebasiK purpose of r':iof washdown is to reduce the radiation dose to occu-

pants of a building by preventing or reducing the accumulation of fall-out on the roof. However, the roof washdown system does not affect t-,;

penetration of the roof h)y radiation from other sources.

It was k)-and that under some circ .mstances a roof washdow-n systemis a useful ueans for increasing the protection of building interiorsand that, in general, the cost of a washdown system for large roof areastructu~res with saooth sloped roofs will be less than the cost of pro-viding an equivalent amount of shielding. However, alied shieldingprovides 100 percent reliability whereas roof washdown systems may notbe as reliable.

CONTENTS

Backgtklund .. ............................. IObjectx 4s . .............................. 2

WASHDOWN EF.'CTIVENESS. ........................ 3

Dose Rates and Dose Considerations. .................. 3Dose Rate from Roof Residual Fallout. ................. 4Transit Dose Rate ........................... 4Dose Rate from Adjaccnt Surfaces. ................... 4Accumulated Doses in Terms of Contributing Components 8

COMPARATIVE COSTS. ......................... 24

OTHER CONSIDERATIONS .. ....................... 28

CONCLUSIONS. ............................ 29

REFERENCES .. ............................ 30

ILLUSTRATIONS

I Example Fallout Deposition Rate ..... .. .............. 5

2 Fallout Accumulation ........... ................... 6

3 Relative Dose Rates from Accumulated Fallout .... ....... 7

4 One Week Dose Components for 10 Foot Tall Structures with

No Shielding Assumed ....... ................... 9

5 One Week Dose Components for 20 Foot Tall Structures withNo Shielding Assumed .......... ................... 10

6 Roof Contribution Percentage (20 Foot Tall, 1,000 Sq Ft

Structure) .......... ........................ 12

7 Stucture Geometry-Dose Reduction Factors .. ......... . 14

8 Roof Attenuation Factors ... .. ................ 15

9 Wall Attenuation Factors ...... ................. 16

10 Calculated Protection Factors for 10 Foot Tall Structures 17

11 Calculated Protection Factors for 20 Foot Tall Structure 18

12 Equivalent Roof Thickness of Washdown System-10 Foot High

Roof ........... ........................... 19

13 Equivalent Roof Thickness of Washdown System-20 Foot HighRoot.... . .......................... 20

14 Required Root Thickness , Obtain a PF of 40 for Structureswith 150 PSF Walls ....... .................... 21

15 Washdown Water Flow Rates ...... ................. 23

16 Additional Cost of Open Truss Root Support . ........ 25

iv

i v :Ag

!: ..

TABLES

1.Cost of an Installed Recirculating Washdawn System

for a 10,000 Square Foot Roof. .. .. .. ............ 27

Iv

INTRODUCTION

Background

Water washdown was originally proposed as a method of preventingthe buildup of seawater fallout on ships' weather surfaces. Performancetests with actual fallout demonstrated that washdown was feasible andcapable of significantly reducing residual contamination levels. Theship washdown system (an older name for it was water curtain") consistedof an automatic sprinkling system, which could be activated upon warning,and could operate indefinitely, using seawater from the ship's continu-ously replenished supply. The constant streams of water functioned asboth a barrier and decontaminant. The water formed a fluid film over theship's qurfaces to dissolve the depositing seawater fallout and preventedmost of the dissolved radionuclides from coming in contact with the ship'sweather surfaces or, if the seawater fallout did contact the surfaces,

the water was intended to dissolve the residue and carry it over the sideinto the ocean. Since the washdown was initiated before or during fall-out, two separate benefits were obtained.

1. A reduced exposure dose to ship personnel during the falloutperiod

2. A decontaminated ship after fallout cessation

It was a natural suggestion that an automatic wasi-lown system mightbe applied, with similar benefits, to the roof of a building for the re-moval of solid fallout particles formed by land surface detonati ons.There are, however, a number of important differences between the shipand the shore applications. Buildings (1) do not possess mobil ity,

(9) generally are not surrounded by an infinite supply of water, (3) arenot equipped with large water-pumping capaLilities, and (4) generally arenot surrounded by an infinitely deep activity sink. Finally, the mecha-nism of removal ,f solid particles is quite different from the mechanismof removal of the soluble seawater fallout that .s produced bv detonationsnear the surface of the ocean. Although the effectiveness of a roof wash-down system has not been tested with real fallout from land detonationsor any other type of nuclear detonation, there are a few buildings in the

country that. are equipped .ith washdown systems..

The present studv is an attempt to provide guidancc on the bas ic ap-plicability and relativye worth of roof washd-wn as a fallout radiationcountermeasure. This type of study is not new. 3, 4 An unpubli shed USNRDLreport by S. Salk nI contained a similar study. The topic was also dis-cussed in a short note by P. D. LaRiviere and H. Lee' (also unpublished).This presentation is an extension of these studies.

Object ives

The objectives of this study are:

1. To determine the feasibility of incorporatir, a roof washdown

system in some structures in lieu of adding shiclding materials

to the roof for the purpose of converting these structures to

radiological shelters.

2. To compare the performance and characteristics if applied shield-

ing with those of roof washdown.

3. To apply a cost analysis as a basis for the selection cf options.

I/I '

ILI

WASHUOWN EFFECTIVENESS

Dose Rates and Dose Cons iderat ions

The basic purpose of' roof ashdown is to reduce the radiat io-I doseto occupants of a building by preventing or reducing the accumulationof fallout on the roof. However, the roof washdown system does not af-fect the penetrat ion of the roof by radiation from other sources. Thus,in addition to the dose rate from the roof fallout deposit, two other

dose rate contributors to the total dose rate received by building occu-pants through the roof mnist be considered, and also the different con-

tributions must be considered over two time periods: (1) the time duringfallout and (2) the time after fallout cessation.

1. Dose rate during fallout

a. Roof deos it dose rate. The source oi this rad iat ion is

the fallout particles that are actually deposited on theroof; its magnitude depends on the roof retention rate(with or without a washidown system) and the amount of fall-out deposited to ia given time.

b . Transit nose rate. The source of this radiation is the

air borne fal lout particles in the air near the 'buildingat aIN~ t inc btefol~k ia norssit ion. The magnitude' ofthis rat. tat ion is no*, iuf. ,ivnced by washdown.

c . Adjtacenit siirf~ice dlose, rate. The source of this a ir-

scat tere-, rad 'ation is ft, ealIlut that haS bee'n Jpos itt en

(aM a g ivcn'i time,) on surr -mdnri roots or grc'uno areas.

The Magnitude of this rad ia tion1 is not tnt luericed b.) wasi-

dow (nsst he systeml is aIS 1oised( o)! thktse areaIS).

A Alt e r ta lout ce, s a t i on

ii th Is pe ri1od t he 1, aI tout part to los have .ll11 e dop--it ed

hvnce the, tran iiU dosU rat is e*O . i'he componunt. off the

A. Hioe! (1epo)s1 kII) dos .I~tC. T;e I So0U re C )f his rai ia ti in i s

tnf:t l lou t pa rt i clos revma ii g hO Th- i , 1 Its rt.gnitudc

depenrds on Ithc nlens It o I t he re.av n 1, do e5 I IS , ant tiie

at tI* doe va (r i~ it on *.!ne to w ei t ho ig VAnd *hecay

1) Ad ,acun t su r tace ktosc rat- r h 50 S tI r Ct r itd Ia t Ion1

I s the fatlo(ut Oex e n SUrround tigh surf acus (ot her

roofs and the grounid).

If a washdown system remor."s a given fraction of the depositing

fallout, independenit of the time after start of fallout, the effective-

ness of roof washdorn can be a~'iroxirnated by calculations using the

fiacti-n remaining after fallout cessation.

Dose Rare from Roof Residual Fallout

As an example, Fig-are 1 is a fallout deposition curve in grams per

ft per time uni-1. as a f-inction of time after detonation . 7 Because- no

data on washdown wash-off rates are available, a wash-off rate of 50

percent of the accumulated fallout mass per 0.1 hoar was assumed. It

was also aassumei that 10 percent of the accumrulated fallout mass was notremovable-i.e., there wouldi be a 10 percent residual.8'17 These r,:la-

v tioaships are expressed as: 1

do,. diim0.1 (2)

dt ZtT

dinm daM 0.52 : ~ m (3)

dt (11t 0.1

Applying these assumptions to Figure 1, Figure 2 was derived in which

comparisons are made of the relative fallout mass accumulation curvesfor no wqshdown and washdown. The third etep was to apply a radioactive

decay function, and the result is F. ',urc , which sho vs the relativedose rates with and without washdown for the fallout period. Inte-gration of the two curves with time gaL, a dose ratio of approximately

5 to I for fallout depos-'ted on the roof only. That is, the dose to a

common reference point from roof fallout w2,-!out washdowi was 5 times

the dose .'rom roof fallout with washadown.

Transit Dose Rate

The airborne transit dose to an unprotect-d location has been vari-ously estimated--from negligible to as high as 20 percent of the deposit

dose ourin-, the deposition period.'0 The portion transmitted throughthe roof of a strrcture as opposed tc the portion transmitted through

the walls is a function of the structure shape and the relative shield-I ing afforded by the roof and walls.

Dose Rate from .'ijacent Surfirces

As for the air-scattered radiatici, which comes from the cncztninated

I

Figure 1

EXAMPLE FALLOUT DEPOSITION %,ATE

4

I.-

~I-

2E

zz0

0

0

U-

0

Uce

I-.-

!.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3,2 3.4

t IN HOURS AFTER DETONATION

-==5

Figure 2

FALLOUT ACCUMULATION

40

38

36

34

32

30

242

20

zsZ 16 /0

t o j4

<10

16 ROOF 2.W22 .S26 D83O32 .

4L-

2

3LL

12.6 1.0 A 2TE0:TOAT2 2.4 2.6 2.3 3 0 3.2 3.4

IN HOURS AFTER DETONATION

.~6i

Figure 3I RELATIVE DOSE RATES FROM ACCUMULATED FALLOUT

20

18

16

j 14

12

10

8

-6

z

ROOF WASHDOWN

U.,

00

00

1.6 1.8 2.0 2.21 2.4 2.6 2.8 3.0 3.2 3.4

tIN HOURS AFTER DETONATION

7

ground or other roofs, its transmission through the given roof is a

function of structural shape, size, and root shielding. 1 The procedure

given in Reference 11 was used to estimate the dose rate transmitted

into the building from deposited radioactive fallout sources. The ratio

of the ground-source radiation that penetrates the roof via air-

scattering and the ground-source radiation that penetrates the building

wall is the same during and after fallout cessation, neglecting the

effects that a changing gamma spectrum might produce.

Accumulated Doses in Terms of Contributing Components

After calculating dose rates, the accumulated ex:esure dose is

deterrined. In order to estimate exposure doses, certain conditions of

the building with respect to occupancy must be known; these includ - the

stay period in the building, the araount of shielding afforded by the

building, the height of the roof from the ground, and the size (area) of

the roof. For the fallout deposition and residual buildup rates shown

in Figure 3, the following conditions were assumed:

Exposure location - 3 ft above floor center

Stay period - 1 week after fallout cessation

Shielding - None (worst case)

Building (roof) height - two values, 10 feet and 20 feet so as to

show a range of heights

Roof size - A range from 1,000 sq ft to 100,000 sq ft

Washdown - One situation using washdown, and another not using it

Under these conditions, the dose components to the occupants of a

building are calculated as a percent of the total no-washdown dose.

Figure 4 is for a roof height of 10 feet. and Figure 5 for a roof height

of 20 feet. As can be seen, the roof rwidual dose with washdown is

appro-imately one-tenth if the roof residual dose without washdown. Also,

the e-,posure dese to occupants from air-scatte., radiation through the

roof is significant for small structures when comparod to the roof re-

-tdual dose with washdown, and the transit dose is negligible.

The dose received through the wallq to a center location in a

building from adjacent ground sources ib seen to decrease with buildirg $area size in Figures 4 and 5. This dose or (ose rate cmponent wuld be

further decreased considerably for below grade locationa, and for upper

8i

Figure A

ONE WEEK DOSE COMPONENTS FOR lOFT. TALLSTRUCTURES WITH NO SHIELDING ASSUMED

100 0

~ %Qc*

10 ck90

LU '~GOUND DO'7

tA 40

0D

0. E

6 O 19,ROFAE zt

Lq

4,

Figure 5

ONE WEEK DOSE COMPONENTS FOR 20FT. TALLSTRUCTURES WITH NO SHIELDING ASSUMED

100

10

05\4I

41C4

0

z

0

10 3 10 4 10

ROOF AREA - ft 2

1 0

story locations. As the dose rate component through the building walls

decreases, rooi protection becomes increasingly important. This can be

demonstrated by using a single structural configuration and calculating

the roof contribution to the total dose rate within the structure as a

function of w.11 thickness. The very thick walls (heavy mass-thickness)

would be representative of a location on the second floor ,f a two story

structure with moderately thick -lls, and the thickest walls would be

representative of a basement location in a structure with a thin roof

and floors. Figure 6 gives the roof contribution to total, dose per-

centage in a 20 foot tall, 1,000 ft2 structure, for three roof mass-

thicknesses and for various wall mass-thicknesses. As can be seen, the

relative roof contribution increases with wall thickness and decreases

with roof thickness. The larger the relative roof contribution, the

greater the relative effectiveness of the roof washdown system. Thus,

if a 10 percent residual washdown system were used upon a structure

where the relative roof contribution was 0.90, the dose reduction due to

the washdown system would be a factor of 5.3. If, on the other hand,

the roof contribution were 0.10, the 10 percent r-sidual washdown system

wrould reduce the exposure dose by only a factcr of 1.1.

The equation for the protection factors (PF) of structures without

a roof washdown system is

= 1/ ( F [A + 1) + E] + FF B) (4)RRT WG3 WT

and the equation for the PF of sLructurts with a 10 percent residual

roof washdown system is

PF *- I H F u + i + F + F FTP (5)R |G Wr W; W

where (see Figures 4 and 5)

A iS the roof residual Jose without washdown

B is the total dose thrLough the walls

C is the roof residual d)se with washcown

1) is tho air-scattered roof-dos from ground sourc-s

E is the transit radiation dGse

U1

Figure 6

ROOF CONTRIBUTION PERCENTAGE (2OFT. TALL,1000FT? STRUCTURE)

100

ROOFCONRIBUON,~ =ROOF DOSEROOFCONRIBTIO, %TOTAL Wz$ X 1 00

:00

o 0

0..0

z

0

z0

U

00

WALL MASS THICKNESS -lb ft'

12

and where (see Figures 7, 8 and 9)

F is the roof geometry reduction f -torRG

F is the wall geometry reduction factorWG

F is th, roof thickness reduction factorRT

F is tue wall thickness reduction factor (To show the variationWT

of F with shape, a range of values was included--i.e., 10WT

and 20 foot walls.)

Figure 10 gives the PFs as a function of roof size for a structure

with a 10 foot roof height, with various wall and roof shielding mass

thickness combinations, and with or without washdown (calculated by the

procedures of Refere- 11). Figure 11 snows the calculated PFs as a

function of roof ize for a structure with a 20 foot roof height and for

the same combinations as in Figure 10. As can be seen from the curves

in these two figures, no thin roof structure with washdown, having less

than 150 PSF wall shielding thickness, qualifies as a shelter (40 PF

minimum). Two options for obtaining a protection factor of 40 (or

better) are: (1) augment the washdown effectiveness with applied roof

shielding: (2) apply sufficient roof shielding to eliminate the needfor the washdown system.

Figures 12 and 13 oresent the equivalent roof mass thickness of the

roof washdown system as a function of roof area for roof heights of 10

feet and 20 feet. By rewriting Equation 5 to read

1-- - F F BPF WG WT

HT F R(CG ( -+D E)

the roof thickness reduction factor required with roof washdown for any

structural geometry, wall thickness, and desired PF can be determined,

and the roof thickness roquired with the washdown system can be obtained

from Figure S. The required roof thickness to obtain a PY of 40 with

and without the roof washdown system for structures wit!, 150 PSF walls

is presented as a function of structure size (roof area) in Figl.are 14.

As can be seen, a relatively thin roof with washdo* is all that is re-

quixod fu;r the 203 foot tall structure--i.e., less than 20 PSF--regard-

less of structure size. This requirement may be comnpared to roof thick-

nesses of 70 to 90 PSF that are required without washdo%. In the case

of the 10 foot tall structures, a relatively thick roof in addition to

roof washdowm Is required for the smaller structures, although a rela-

tively thin roof is adequate for the larger structures. On _2vii other

hand, if the wall tilickness of the 1O foot tall structures were increased

13

Figure 7

STRUCTURE GEOMETRY - DOSE REDUCTION FACTORS

1.0

0.9

0.8

0.79v

0.6

0.4

0.3

L 0.2

0.. 10~

i 0

ROOF AREA - ?

Figure 8

ROOF ATTENUATION FACTORS

1.0

EN

N21

L - r. I

4 I b~~a ,zr4 j

Figure~

WNALL AllTEINUATION f-ACT(ORS

0

4U

0

Ui

0.00 00030 0

SHEDN4ASTIK ESI-

z1

Flaure !O

CALCULATED PR.OTEICTMN FACTORS FOR 10FT, TALLST RU CT U S

100 .........I

ne.-

1117

Figure I

CALCLATED PPRO7EC-T!O-, FACTORS FOR 2QFT. TALLSTRUCTURES

1 00

100

I I

j~jU

z0

10 10'41

ROOF AREA -ft 2

18

00Lhr

0

-JJ

Uci

Z -- o

0 Cc

0 c

LIL

o

z2IN A

0 >0(Noi 8 0 orN0 -5

4bs!91 SS3N)ADIHI SSrW*

19

(0C

04

(A 41,

00

z 0

o -

04

oL 00

Z 64

202

z0

0I z

0 00 00 0t

0 0 0

LA- 6

0 <

- C-

06

(SN'j~l S4

z2

Ito 175 PSf, then thin roofs (less than 20 PSF) with washdown would also

be all that would be required for the znmaller structures.

All the above calculations are for a location at the center of the

structure and for uniform wall thicknesses and uniform roof thicknesses.

At locations away from the center of the structure, the roof-dose/wall-

dose ratio will change. This variation will not affect the equivalent

roof-washdown, roof-mass-thickness values in Figure 12, and unless ex-

treme locations (e.g., corne, locations) are used, the PF values in

Figures 10 and 11 and the required roof thickness values in Figure 14

will not be significantly affected.

For very large roofs, tie effectiveness of roof washdown systems

will be degraded because of the greater amount of fallout that must be

carried by the water stream. It is not known what additional amount of

water, if any, woula be required to overcome any buildup effect that

might occur with heavy rates of .fallout upon large roofs. Figure 15

shows R suggested washdown flow rate for relatively smooth roof sur-

faces. 44 Washdown effectiveness data for various flow rates over longer

distance (>50 feet) are nonexistent, and consequently the flow rate re-

quirements for roof areas in excess of 10,000 ft are represented as

dashed lines in Figure 15. Finally, the roof washdown system could be

reduced to partial or total ineffectiveness by malfunctions or from

freezing at extremely cold temperatures.

'2

Figurel 5

WASH~OWN WATER FLOW RATES

0'

II

I/

/I

//

/

/

, ---.- - -

--

4

I

1'

RC)Of A~A

23

COMPARATIVE COSTS

The relative cost of converting conventional structures into shelterseither by increasing the roof mass-thickness or incorporating a roof wash-

down system (along with increasing the wall thickness) depends upon how

the original building was constructed. The cost also depends upon the

choice of roof %ohdDwn system and the choice of slielding materials.Some structures are not suitable to :Dnversion to shelters by the mere

application of additional shielding materials on the roofs, and washdown

systems are not suitably effective for the roofs of some structures. For

such structures tle relative costs are indeterminant.

In general, sloped or pitched roofs are suitable for rocf washdown;

and flat roofs, if they are adequately strong or are amenable to rein-forcing, are suitable for applied shielding. On occassion, there are

structures with roofs that are suitable for roof washdown as well as for

applied shielding. The relative cost of applying shielding or installing

a roof washdown system may be compared for these structures. Usually,these structures are of medium to heavy steel construction (the roof sup-

port includes girders and open truss joists), have concrete for roofingmaterial (2 to 4 inches thick), and have a slightly sloped roof (e.g

1:24). The weight of these roofs ranges from about 40 pounds per squarefoot to about 60 pounds per square foot, and is designed to support live

weights of 60 to 100 pounds per square foot.

It additional structural strength is requircd to supp -t the added

roof shielding weight, the cost of providing roof shielding is increased.

The construction cost of additi onal roof support lor a 20 toot span andfor a 30 toot span on an open structural frame lz, giver, In Figure 1t. 6 .It the structure to be modified is finished with ext, -lor and intcriorwalls, and with root and ceiling, and the interior I., compartTilented. the

cost of applying additional structural strength Aithuut degrading; usulul-ncss and aestfhet is i-s very , high, and the overall cost could run a- high

,i.i, or higher than, the cost ot new cnst ru t ion. 01 the, othel" ha.d, i orstructures that do not r.quire addit lonal structura l rcnh the ot

o. applving root shi.ld.In odr th,. exist ing roof is mere''l, t h, oSt 01

the shitIding material and the cost of labor. The coSt of Six luelits 01

reinforced oncrte in pla.:e Is approximatel, $1.00 to $1 25 per square

The cost oz Installing a rLoof washdo'wn Sst em i a st rucltnr , ll

dt.-pind upon the rool type and *he t vpe ot washdow. -ste V C A s mooth we -

sloped roof requi res less atter and Leweter .ozis than it roo .hat I-,

24

F igure 16

ADDITIONAL COST OF OPEN TRUS, ROOF SUPPORT

2.00

1.50

I.C~/

DEA Mk--H.1AN DEIGN D OADfN.' 'L

2

rough or has only ,slight slope. Three types of washdown systems are

described as foilows:

1. "Once through,' using the normal water supply .

.'Once through," usi~ig stored w9ter or well water, or drawing

from a natural body of wat, r.

3. Recirculating, using t .ed water.

The first type is the least expensive and tnte least reliable be inrg

entirely dependent upon an unimpaired water system. The basic components

are piping and nozzles (it may be assumed that, for large structures,

adequate drainage exists). The cost of such a system depending upon theshape, texture, and slope of the roof, will range between $0.10 to $0.40

per square !o~t.

The second type is practic:al only it a high capacity well source or

a body ot surface water is located nearby. The cons!truct ion of a storagetank with sufficient caSpaclty for a once through system is 0,orbi ta nt.

If it is necessary to dig a well and install a pump (internal combustion),or if it is necessary to install a pump anid a long water, line to the

nearest body of water then thu third type of %.ashdown syst em will be

more eccont,nical as well as more reliable.

The third type ot washdown system consists uff (1) a water- arid

tallout ccllection system, arid (2) a water- storage anid 1,iltral ltio syStemr

as well as the piping and nozzlles In som,- strucLur-es adequate collect ing

systemm, exist , anid only, fndificatilons are needed to channel the return-1

water arid fallout to a combi nat ion f ilter anki storage tank. In other

st ructures nvith roof drainage to the e es, collect ing g utters must benst a 1led. St anda -d rein gut ters are i nadequa t e -special larger gut trs

with a btto m slope of at least 1:16 are rec nmended . alt hough there

have been no tests o4 'his part ot -washdovn rvt~; hese, spec li I

gut tifs will ',) more c-ost lv and will be less ethttc l JppcaJ111ng

thin standard root gAtters,.

Ext rta p ipji ng o r t ndu i ts wA 1 1bev requ red to c ary 1, he -olI lec ed

wAater and fallo1ut tm) a 'et t lIng chamber,. which should hie instailled helow

g;round so thiat t hevcol lected tal lout *ill Lcshele

A settling Itnk i~nl a oa rse tilt er aire al -! 7" j t csav

ruVM01e the' Ull0ut oarlti icls !rtn the% rc r d r ie*e to

re-qulremen ts are 0st imtattd at 0 2 Ia. glinspol Squa J A t

and t hl s t w In inm udt-: th F! oli fIh e Ii g 'p~m 2 i

1)u .pin:1g rat I i s e t I rna t L, k at1 0 kl t o g.. ga I I I pvr M nmm'1 po r kqu.)r t

tout k rot urea (,see Hcreni v S1 or I orage takd g)z

:26

lb. ,4at12r requirem its I or adequate ro() cove rage depend upon the

root textureU, Co0t slo ad r-of shp.Table I gives the 'ost f or

ht OnUt or-ll0,1t t h, '' rcu eit ing washdown s' .te ( i Ih the inst allat inSos t I 1lk Intided) anId t he Ia ct I .- at I ect inog t !L cost ~,rsquare f oot of

root. I! a co wimoent e_ x t ts a s a p ar t <.t fi' st rue ture design or 2 s a!10rMa I I ae 1ili ty NComponen~l!t or 1't thfe (OMPo11llt 1 )t need ed fo 0t- ,he tPC

ot wa h1own I oivs tem des i rt-d ,t he- ost oft thle yornpoflnrt miay be subt ractedIroin% tino tot al ot.Fo( t Ir bae opon a 10000 Sq I t :-oof size.

fh(2 uIt (Ost A il be hi gher' i or -ini, 11cr rootIs a nd slight lv low for,

COST OF AN INSTALLED RECIRCULATIN6 WASHlI3JWN SYSTEMFOR A 10 ,000 SQUARUE FOOT ROOF

Component F1-a t or AtIic teC ll us t Cost -s I t

hoof pingl alnd Roo: texture, roof slope., 0. 10 to 0.10

iio"Zl es too" Shape*

Nttel' rt urn'! SstLP em ih tetoreV ro "lope)

ma.1t e' C a I L!S (2d G 07 to 0. 12

St erage tank Roo! 'extuic . rvoof lope.rot shapet soil 'Lpc 0'09 1o 0 lXI

Pum RuLt t 1 0i 1w.ie)Lp

roo. _- ha pe , r o oI K h 0 0 T t L, 0). l1)

ho 3' a' 0 SO

11Wnc M t bree fact ors determinle the punmpi g rate, tootvig*v 0);' piping,

number of nozzles-, the- return Myvsttem capaicit , and the, stor>

tanlk Size.

27

OTHER CONSIDERAIONS

The e-.valof flotfrom rosbv the washdown sy'sten is-.p-ventive mea'sure against the contamination o'f othe- r targe~t area:; ) ori--n1ally deposited roof fallout that would otherwise be subtsequontiv reui,,-tributed by the wind. Washdos,;n niay also eliminate the flec ss;.t- for roofdecontamination after shelter emergence. On the other hand, the rco.washdown system does not add to the structural strer ,th of the buildinrs,-nd therefore it is a countermeasure only against fallout radiation.

To add shielding materials to a roof IAchout adding structuralrnprov'Pment does not increase structural !s rength, and 1Pn fact, ;I-P

decrease structure strength. However, such an addition ol shieldingmaterials is "dirt cheap", and some shielding materials such as rein-forced concrete. when added to the roof along with structural Improve-ments, would increase structural strength. Thus, a building witihI a rein-forced concrete roof plus structural. improvements will be ecjuippted notonly with a countermeasure agains t fallout radiatio!,, but alsv an ).ncr;!:Psddegree of protection against blast (2nid perhaps fire) effects.

The comparison of roof shielding with roof washdown effectivene ssassumed 100 perce,t root retention of fallout for the no-washdown cc rn-dition Under some wind conditions, a very high percentage of the fall-ouit on smooth slope roofs would be blown off the roofs. aFallout onthese routs wc-ld also be washed away by rain. The wind erosion oNf fa.1l-out even fr,,m rather roughi 11lt root's could be cons ideraoble---50 pejce'.,dos- rate reductions ron flat tar and gravel roofs within tine ftrst48 hours by moderate to high winds were recorded radiological recoverystudies conducted by the U.S. Naval Radiological Defense Laboratory at

13Cvnip __irks,

The calculations comparing roof shield~ng with roof washdown effec2t-iveness .'so did not inc ide the effects of fallout sc'lubil ty and roofsurface ausorptivity. If the degree of fallout solubility and roof sur-face adsorptivity is significant, the _' tiveness of the roof washdown

system wc-ild be adversely affected. The effects of fallout solubilitv

a nd roof skurace adsorrtion would be worse with the recirculating roofwashdown system.

Finally, a structure that is protected by applied shielding can berelied upon to provide the designed protection when it is needed. Witharoof washdowi system, on the other hand, malfunctions ccul. occur that,

could make the syst.em incotwrative. The pump engines may not start when

called upon, the nozzles may be plugged, the water and fallout convey:nnceIs.ystem miay be overloaled, and the filter system may be clogged. Althougha rouitine maintenance and testing schedule would increase the reliabilityof the system, absolu~e leliability at all times cannot be guaranteed.

COSCLVS :ONS

1.The elfectjven;ess of a roof washdown system _s limited because cur-

~ni~.aa~shsroo*)f -,shdon syst~ms do not remove all the depositingf~illo,,t p~vtictles. 7tnd consequentlY d;ome additional roof shielding!,_-)I :often be zec-_jiied to pro-,Ide an acceptable degree of overhead--edxa - on vrotcct -on.

4;. A ro< hdw Y~sten; c-1-not be directly compared with applied shield-I_ ig bwlsOo 2etllowing rea'-,ons:

Apldshi;:Il:i W;zTild be 100 percent reliable and roof washdownoza !ait L'C e

b. Wind <,, ra;.n csn be e~~~rto irmove some (,, the fallout fin,mouth s2op--d ro_ ,fS, Such w., atber elfec..s would probably not

r~cnzetherads~in rc-i rtcif s.~nrc-s n.removed by roof wash-oow 'r, but. the,, wo'.j -ces _4 ation fizm shielded roofs

.HAnv St.,%Ictures ar, soti.e Jr ta d,, -on of applied±~he~dngar4 a !,hd _,n systelo

3 .A rocof washciowa sysle:i is ucIA c" craigthe protectiono~ bu ig i Pt 2 i ors, ; 1 u t _-i o, ~~ ie~ t h- f ollIowi ng con -d I ~ion5s

a. Tem;,eratui-e n igh r t h_-in tne tz~x t which~ the watersol~dfii:. the -Ipej .r ze or az<i~; h sprav f-orms

sn,-)" oz- Lheet_, 01: .ce On the -'ozf.

b, The -roof is slcqwd 3nd tin r, at 3D'.cth kuriace.

C.The syst.em h ;.o been de igred aisd to .p_ t -rate indepen-dently ofotiepoWer So;zC xin zan upfe assure

rel iabli r v.

d. The structur , eqkapned with w ~c~~S' not dt ;gted by blast (anoperit-Ing roof wa s~znw, rv tt~m con id, ~'eedecrease firehazartiL in peripheral L.,St aroosq)

4. 1;, Qlp~. tb co ;t c. 3i t sdenxn 4i em teoz, lrge roof area st ruc-Ures vitn wiv~oi.A skae.- roo! Wi 21 btz L han tho cost of 'providing

an equi,<,eolt-t anioun t f sxiif:,dlnrg

29)

REFERENCES

1. Molumphy, G. G. , et al, Proof Testingof Atomic Weapons Ship Counter-LmeaSUres, U.S. Naval Radiological Defense Laboratory, Project 6.4,Operation CASTLE, WT-927, October 1957 (CLASSIFIED)

2. Protective Features of the Fort Worth Air Route Traf fic ControlC enter, Federal Aviation Af-ency, Inspection Repor't. August 1961

3. Kehrer, W. S., and M. B. Hawkins, FL~sibility and Applicability ofHoof Washdown System, U. S. Naval Radiological Defense Laboratory,USNRDL-TR-232, May 1958

4. Owen, W. L. , Radiological Protective Construction, U. S. NavalRadiclogical Defense Laboratory, USNRDL-467, January 1962

5. Salkin. S., The Effectiveness of Roof Washdown Systems in theReduction of Radiation Intensity in Buildings, U. S. Naval Radio-

logical Defense Laboratory (unpublished)

6. LaRiviere, Philip D. , and Hong Lee, "Notes on Roof Washdown",Stanford Research Institute (unpublished)

7. Miller, Carl F., Fallout and Radiological CountermeIsures, Volume I.

Stanford Re.-earch Institute, Project No. IMU-4021, January 1963

S. Heiskell, R. H. , et al, Design Criteria for Roof Washdown~a e,Phase 1. Fallout Removal Studies on Typical Roofing Surfaces f-rTwo Size Ranges of Particles (177-350ji, and 350 5. ) , U. . N;av31Radiological Defense Laboratory, USNRDL-TR-672, July 1963

9. Heiskell, R. H. , W. S. Kehrer, and N. J. Vella, Dein Criteria for,Roof Washdown, Phase II. Fallout Removal Studies on Typical RoofingSufc sfrT,,eSz a 0 Particles (444 to 884- 88 c 17

arid 590 to 11906) U.S. Naval Radiological Defjense Laboratory,UsmlTrT7TAll igust 1964

10. LaRiviere, Philip D. , Hong Lee, and K. X. Larson, IoiainRotofMeasuremen ts (U) , U. S. Naval Radiological Defense Labora'tIory,

Project 2.11, Operation SUN BEAM, Shot Small Boy, POR-2217, September1962 ((:aASSIFIED)

11. Lee, Hong, Radiological. Target Analysis Procedures, Starford ResearchInstitute, Project. No. MU-Y5069, March 1966

12. Clark, Donald E. Jr. and Hong Lee, Ceniza-Arena Cleanup in San

lose, Costa Rica: Operational Aspects as Related to Nuclear WeaponFallout Decontamination, Stanford Research Institute, Project No.MU-5069, May 1965

13. Owen, W. L, and J. D. Sartor, 'adiological Recovery of TargetComponents--Complex III, U. S. Naval Radiological Defense Laboratory,USNRDL-TR-700, November 1963

14. Engineering News-Record, May 5, 1966

15. Walker, F. R., The Building Estimator's Reference Book, frank R.Walker Company, March 1954

'I

31

7ITLE: An Analysis of Roof WashdownVersus Applied Shieldingas a Fallout Countermeasure

By: Hong Lee

SUMMAR Y:

An analysis of roof washdown systems as a fallout radiationcountermeasure is presented. The effe :tiveness of a roof wash-down system in reducing the exposure dose ,ate to occupants of abuilding is compared to that of adding shielding materials to theroof for various buiiding geometries and building wall mass-

thicknesses. The relative costs for the two countermeasure meth-ods are also compared as weil as their relative reliability. Thefindings are that the cos, of a iashdown system for large roof areastructures with smooth sloped roofs will generally be iess than thecost of providing an equivalent amount of shielding but the systemwill also be less reliable,

SRI Project No. MU-580b December 1966

Contract No. NOO22806CO231

OCD Work Unit No. 3231C

TITLE: An Analysis of Roof Washdown

Versus Applied 3hielding

as ; Fallout Countermeasure

By: Hong Lee

SUMMARY:

An analysis of roof washdown systems as a fallout radiation

countermeasure is presented. The effectiveness of a roof wash-down system in reducing the exposure dose rate to occupants of a

building is compared to that of adding shielding materials to theroo, for various building gt ometries and building wall inass-thicknesses. The relative co'sts for the two counterneasure meth-ods are also cornpared as well as their relative reliability. Thefindings are that the cost of a wa shdown system for large roof areastructures with snmooth sloped roofs will generalllv be less than thecost of providing an equivalent amount of shielding but the syster iwill also be less reliable.

SRI Project No. MU-,806 Deceiiiber I t9t,

Contract No. NOO22866C0231OCD Work Unit No. 3231C

I

UNCLASSIFIED _

DOCUMENT CONTROL DATA 4 & D

STAN*'RD RESEARCH INSTJITUE UNCLASSIFIED

Menlo Park, California 94025

AN ANAiLSIS OF ROOF WASHDOWN VERSUS APPLIED SHIELDING

AS A FALLOUT COUNTERMEASURE

Lee, Hong (nmn)

Decemaer 1966 31 15e. SNHAC C a R k N Itotto A'CR'S asIt

N0022866C0231

OCD Work Unit No. 3231C

SRI Project N . IU-5806 'P 7. .

This docunit-nt hr- been appiu~td for public i-lease and sale.

Its distribution is unlimited.

Office of Civil Defense

Department of the Army- Washington, D.C. 20310

This study provides guidance on the basic applicability and relative worthof roo washdown as a fallout radiation c-untermeasure. The basic purpose ofr1)(i4 washdown is . reduce the radiation dose to occupants of a building by pre-

venting or reducing the accumulat ion of fallout on the roof. Iowever, the roof

wAashdown system does not affect the penetra ion of the roof by radiation fromother sources.

It was found that under soime circumstances a rot washdown system is a useful

MeaiS f0r Increasing the protect tion of building interiors and that, in general,

th- ,ost of a w' shdow-n system for large roof area structures with smooth slopedroo , twill be less than the cost of providing an equivalent amount of shielding.

Fowtbver, appl.Lud shi(lding provides 100 prcvnt reliability whereas roof washdownsystems may not be as reliable.

DD FORMS1, 7 (PAGE t!SS) ~DD 1o4,..a7., S,,,".UN IAS FI2

UNCLASSIFIED

~I N

C-ivil Defense

Rad iologi calFal1lou t

S heliter

Was~h down

Shielding

Countemieasure Sys~em

DD -O 473 17 IA L~ I I~ 1fl

P A, I

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