AL-TR-1992-0139

AD-A260 255

INDUSTRIAL HYGIENE EVALUATION OF

A F-111 FUEL TANK SEALANT PROCESS

RMST Robert Walton, Captain, USAF, BSC

R OCCUPATIONAL .AND ENVIRONMENTAL0 HEALTH DIRECTORATE

2402 E DriveN Brooks Air Force Base, TX 78235-5114

G

L December 1992

A Final Technical Report for Period January 1091 - October 1991

B0R Approved for public release; distribution is unlimited.AT0RY ODTI

eFES 1993 93-030130 3 I iM I Eli M ! MII IU ]]'1•r •

98' 2 16 127AIR FORCE MATERIEL COMMAND

BROOKS AIR FORCE BASE, TEXAS

NOTICES

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The mention of trade names or commercial products in this publicationis for illustration purposes and does not constitute endorsement orrecommendation for use by the United States Air Force.

The Office of Public Affairs has reviewed this report, and it isreleasable to the National Technical Information Service, where it will beavailable to the general public, including foreign nationals.

This report has been reviewed and is approved for publication.

Government agencies and their contractors registered with the DefenseTechnical Information Center (DTIC) should direct requests for copies to:DTIC, Cameron Station, Alexandria VA 22304-6145.

Non-Government agencies may purchase copies of this report from:National Technical Information Service (NTIS), 5285 Port Royal Road,Springfield VA 22161.

CRAIG H. HOLLENBECK, Maj, USAF, CIH MARK H. STOKES, Col, USAF, BSCChief, Industrial Hygiene Branch Deputy Chief, Occ Med Division

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1. AGENCY USE ONLY (Leave blank) 1 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

I December 1992 I Final Janua 1991 - October 19914. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Industrial Hygiene Evaluation of F-ill Fuel TankSealant Process

6. AUTHOR(S)

Robert Walton

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) S. PERFORMING ORGANIZATION

Armstrong Laboratory REPORT NUMBER

Occupational and Environmental Health Directorate AL-TR-1992-01392402 E DriveBrooks Air Force Base, TX 78235-5114

9. SPONSORING/MONITORING AGENCY NAME(S) AND AODRESS(ES) 10. SPONSORING/MONITORINGAGENCY REPORT NUMBER

11. SUPPLEMENTARY NOTES

12&. DISTRIBUTION I AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

Approved for public release; distribution is unlimited.

13. ABSTRACT (Maximum 200 words)

This report presents an informative, inclusive and concise evaluation ofa new tank sealant process. Recommendations are made based on air samplingresults and current industrial hygiene practices. This report will aid thosebases implementing this new process in selecting the proper protective equip-ment for workers and in determining where and what to sample for when docu-menting worker exposure.

14. SUBJECT TERMS 15. NUMBER OF PAGES

Fuel Tank Sealant Process 3816. PRICE CODE

17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACTOF REPORT OF THIS PAGE OF ABSTRACT

Unc-lassif ied Unclassif ied IUnclassif iedNSN 7540-01-280-55OO Standard Form 298 (Rev 2-89)

1i Prescribed by ANSI Std Z39-18298-102

TABLE OF CONTENTS

Page

INTRODUCTION .................................................... 1Purpose and Scope .......................................... 1Background ............................................... 1Description of Operation.................................. 1Methods ..................................................... 2

DISCUSSION ....................................................... 2Findings ................................................... 2Sealant Materials and Chemistry ............................ 4Personal Protective Equipment .............................. 5Confined Space Entry ....................................... 5Waste Stream Discharge ..................................... 7

POTENTIAL HAZARDS ............................................... 7

AIR SAMPLING STRATEGIES AND RESULTS ............................ 8Sample Results Within Tank ................................ 8Sample Results From Mixing ................................ 15Sample Results Within Hangar .............................. 15

CONCLUSIONS .................................................... 16

RECOMMENDATIONS ................................................ 16

APPENDIXESA Vulcanization Mechanism ............................. 17B Air Sample Results ................................... 19

LIST OF FIGURESFigures

1 Fuel Tank ............................................ 32 Sampling Points of F-ill Aircraft 22 Jan 91 ........ 93 Sampling Points of F-ill Aircraft 23 Jan 91 ........ 104 Sampling Points of F-ill Aircraft 24 Jan 91 ........ 115 Sampling Points of F-ill Aircraft 25 Jan 91 ........ 126 Sampling Points of F-ill Aircraft 12-16 Aug 91 ..... 137 Sampling Points of F-ill Aircraft 30 Oct 91 ........ 14

aooession ForKTIS GRA&IDTIC TABUnannoncoedJustlfication

DTIC QUALUT INMP 3 By

Distribution/

iii Avallability CodeeAvael sdor

i~st Speolal

INDUSTRIAL HYGIENE EVALUATION OF F-111 FUEL TANK SEALANT PROCESS

INTRODUCTION

Purpose and Scope

In response to a 12 Oct 90 letter of request from theMcClellan Air Force Base (AFB) Bioenvironmental EngineeringSection (BES), we conducted an initial industrial hygieneevaluation of this new sealant process. Three separate surveys(22-26 January 1991, 12-16 August 1991, and 29-31 October 1991)were performed at McClellan AFB during actual spray sealantoperations. Additional air sample results included in thisreport were done by Lt Devine of BES during September and October1991. The purpose of the surveys was to conduct a thoroughindustrial hygiene evaluation of this new fuel tank sealantprocess. The ultimate goal was to determine how the processcould be safely implemented and to provide that documentation toother Air Force Materiel Command (AFMC) bases.

Background

The F-111 fuel tank sealant process is new to the Air Forcebut has been used successfully by civilian industry for sometime. The F-111 has had a history of fuel tank leak problems andtherefore was a good candidate for testing the new sealantprocess.

Description of Operation

The process consists of a number of different operationswhich must be performed in a certain order. It begins with fueltank de-sealing where all the old sealant is removed bywaterpicking. The old sealant surface is prepped using a wirebrush and wiped down with Turco 6628. The sealant surface isthen primed with a Desoto epoxy primer which takes 30 to 60minutes, depending on tank size, when using a spray gun (airpressure @ 30 ± 5 psi and fluid pressure @ 4 + 1 psi). Theprimer coat requires a 30-minute to 45-minute drying time priorto sealant application. The sealant application requires twocoats to ensure proper coverage. By applying white and blackcoats separately, sealant coverage for each coat can be easilydetermined by visual inspection. The sealant is also appliedwith an air-assisted airless spray gun (fluid pressure is 500 psi@ pump but decreases to 30 psi @ gun tip); each applicationrequires between 1.5 to 3 hours per coat depending on tank size.The current procedure requires a 3-hour drying time betweensealant coat applications. During spray application, the tank is

1

ventilated by two supply hoses and two exhaust hoses to controlthe explosive hazard. After the spray application is finished,the tank should be continuously vented by one exhaust hose for aperiod of 7 days to control the solvent off-gassing duringdrying. A technical order on sprayable sealant procedures iscurrently being drafted.

Methods

Standard National Institute for Occupational Safety andHealth (NIOSH) Analytical Methods were used for the sampling andanalyses of air contaminants except for isocyanates, l-methoxy-2-propanol acetate (PM Acetate), and diethyltoluenediamine (DETDA).For these compounds, sampling and analyses were performedaccording to manufacturer-published methods; there is nopublished NIOSH method.

DISCUSSION

Findings

Ventilation: The first point that must be noted is that theF-111 fuel tank sealant process cannot be performed safelywithout the use of local supply and exhaust ventilation. Theconstituents which make up the primer, especially toluene andmethyl ethyl ketone (MEK), present an extreme explosive hazardwhen sprayed in the confined space of the fuel tanks.Furthermore, the configuration of the tanks with multiple baysoffers a challenge for eliminating concentration pockets evenwith local ventilation. Fortunately, we were able to overcomethat problem with a dual push-pull system utilizing pre-existingopenings within the fuel tanks. Figure 1 shows how the air issupplied at two locations from the middle top of the tank, whileair is exhausted from the top at each end of the tank. Theoperation is currently being performed in Hangar 251 and utilizesan HDU-13 for supply air and a pre-existing overhead vehiclemaintenance type exhaust system with a makeshift booster. Thecurrent system has adequately controlled the explosive atmosphereproblem in the tank during spraying, but it has some otherproblems that MUST be addressed. The primer coating appliedfirst to the tank has a consistency similar to paint andtherefore has problems associated with local exhaust of paintingoperations. The most important consideration is the particulateaerosol formed by the overspray. The current system lacks aparticulate filter, and the paint particles are being depositedwithin the ducting of the ventilation system. The accumulationof the paint particles presents fire and explosive hazards,especially when the booster system does not have intrinsicallysafe motors. Obviously, the booster system should contain

2

"I€

I-•

3

intrinsically safe blowers and a Class 2 flameproof particulatefilter. Filter installation may cause a problem with tankventilation flow rates. The increased filter resistance willdecrease the exhaust flow rate, thereby causing an imbalancebetween supply and exhaust air flow. We recommend you let yourCivil Engineering ventilation experts design a balanced systemfor you.

NOTE: All accessible openings are covered on the tank beingsprayed.

Sealant Materials and Chemistry

1. Solvent Wipe Down: Turco 6628

a) Principal Ingredients - toluene, ethyl acetate, MEK

b) Material is used as received and is not diluted

2. Primer: 3 Part Epoxy Primer from DeSoto

a) 519X303 - Primer Base

b) 910X357 - Activator

c) 020X324 - Solvent Reducer (Not used in this process)

The primer is mixed just prior to application with a ratioof three parts Primer Base to one part Activator. The hazardfrom this material can be broken into two fundamentally differenttypes. First, there is an explosive hazard from the majorsolvent components, i.e., MEK, n-butyl acetate, and toluene,being sprayed in a confined space. Second, there may be possiblehealth effects due to exposure to strontium chromate and toluenediisocyanate monomer (TDI). It is important to note, however,that these latter two constituents present only an airborneparticulate hazard because of their lack of volatility.Therefore, they only present a hazard to personnel directlyexposed to the paint spray mist; i.e., only to personnel sprayinginside the fuel tank.

3. Sealant: 2-Part Polyamine Curing Agent Compound fromPRC.

a) PRC 2911 Part A - Activator. PrincipalIngredients - diethyltoluenediamine (DETDA) and1-methoxy-2-propanol acetate (PM Acetate)

b) PRC 2911 Part B - Sealant Base. PrincipalIngredients - PM Acetate, methylene bis(4-cyclohexyl isocyanate)(HMDI), and HMDIpolythioether pre-polymer

4

The sealant is mixed just prior to application using a hand-held pneumatic mixer with a one-to-one ratio between parts A andB. Again, mixing changes the constituent concentrations fromwhat is indicated in the MSDS to 50% PM Acetate, 40% HMDIpolythioether pre-polymer (according to John Zook, PRC chemist,only 2.5% of the 40% is unreacted HMDI terminal groups), 2.5%HMDI monomer, 2.5% DETDA, and 5% pigment. The explosive hazardduring sealant spraying is significantly reduced compared to theprimer because PM Acetate is much less volatile. As with theprimer application, most worker exposure to these materials willoccur during spraying and only within the confined spaces of thetank. This proximal effect is due to the non-volatile nature ofthe contaminants which generate a particulate aerosol hazardonly. Refer to Appendix A for a diagram of the vulcanizationmechanism.

Personal Protective Equipment (PPE)

PPE, worn by workers to protect them from a hazardous workenvironment, is used while engineering controls are beingdeveloped or when appropriate engineering controls are stillunable to adequately eliminate the hazard. It is NEVER used inplace of engineering controls. In this particular case, PPE isused to supplement existing engineering controls to reduce theworkers' risk. There are really three different exposure groupswithin Hangar 251: the sealant mixing operator, the sealantspray applicators and workers not associated with the sealantoperation. All require different levels of protection. The lastgroup has no exposure to the material and, therefore, does notrequire any PPE. Current procedures require the mixer to wear afull-face dual cartridge organic-vapor respirator, cottoncoveralls with a polyethylene-coated Tyvek suit including bootsand drawstring hood on top, and Ansell/Edmont nitrile gloves.All openings in this ensemble must be taped to prevent any skinexposures. A portable ventilation booth is being procured formixing operations. Current procedures require the sealantapplicators to wear full-face, positive-pressure, air-suppliedrespirators, cotton coveralls with a Sarnex 23P suit includingboots and drawstring hood on top, and Ansell/Edmont nitrilegloves. Again, all openings must be taped to prevent skinexposures. Heat stress became a problem for the personnel insidethe tank; consequently, a whole-body cooling suit system wasprocured and seems to work very well. The method of operation isvery simple. A small pumping unit circulates ice water withinnarrow plastic tubing woven throughout a cotton suit.

Confined Space Entry

According to the proposed Occupational Safety and Health

Administration (OSHA) standard, Title 29 of the Code of Federal

5

Regulations (CFR) Part 1910.146, the F-Ill fuel tank must beconsidered a confined space. However, the new AFOSH Std. 127-25governing confined space entry specifically excludes fuel cells.Volume 54, Number 106 page 24102-24110 of the Federal Registercontains the proposed rules and defines a "permit requiredconfined space" as an enclosed space which:

1. Is large enough and so configured that an employee canbodily enter and perform assigned work.

2. Has limited or restricted means for entry or exit.

3. Is not designed for continuous employee occupancy; and,

4. Has one or more of the following characteristics:

a. Contains or has a known potential to contain ahazardous atmosphere.

b. Contains a material with the potential for engulfmentof an entrant.

c. Has an internal configuration such that an entrantcould be trapped or asphyxiated by inwardlyconverging walls, or a floor which slopes downwardand tapers to a smaller cross-section; or,

d. Contains any other recognized serious safety orhealth.hazard.

Thus, according to the OSHA definition, the tank should beconsidered a "permit required confined space." On page 24103 ofthe proposed rule OSHA, sets forth the entry permit program as:

1. Hazard Identification

2. Hazard Control

3. Permit System - Requirements set forth in 1910.146 (d)pg 24103.

4. Employee Information

5. Prevention of Unauthorized Entry

6. Employee Training - Requirements set forth in 1910.146(e), (f), and (g) pg 24104.

7. Equipment

8. Rescue - Requirements set forth in 1910.146 (h) pg 24105.

6

9. Protection from External Hazards

10. Duty to Other Employees

Waste Stream Discharge

All of the material exhausted by the ventilation system isvented through the roof directly outside- Due to the compositionof the material being sprayed, even without a filter, only thesolvents would actually be discharged to the outside air. TheEnvironmental Management Division at McClellan AFB has statedthat, at the current usage levels, the mass of volatile organicchemicals (VOC) does not violate current California StateRegulations. Again, we highly recommend use of an in-lineparticulate filter.

POTENTIAL HAZARDS

The solvents in the material combined with the confinedspace of the fuel tank produce an explosive hazard during sprayapplication.

The strontium chromate contains hexavalent (Cr+6) chromiumwhich is listed as a human carcinogen by the International Agencyfor Research on Cancer and the National Toxicology Program and asa potential human carcinogen by the American Conference ofGovernmental Industrial Hygienists (ACGIH). The Cr+6 form istreated differently than the trivalent (Cr+3) form because Cr+6is readily absorbed by the body while Cr+3 is not. An ironicpoint to note is the damage to the body is caused by thereduction of Cr+6 to Cr+3.

Between the primer and sealant material, three differentforms of isocyanates are used: Toluene diisocyanates (TDI), HMDI,and HMDI polythioether pre-polymer. The hazard stems from theextreme reactivity of the isocyanate functional group (N=C=O).Isocyanates are doubly dangerous because they will readily reactwith the moisture in the skin as well as any of the mucousmembranes. They are potent sensitizers and once sensitized,exposure to levels far below the threshold limit value (TLV) willstill elicit a reaction. Again, it is important to note that,because of the extremely low volatility of the isocyanates, theypresent an airborne particulate hazard to only those personnelexposed to the spray mist.

The sealant contains a secondary amine DETDA which activatesthe isocyanate and begins the vulcanization mechanism. Themanufacturer, Ethyl Corporation, has performed a two-year study

7

on rats. It should be noted that two years represents a lifetimeexposure in rats. Results indicate possible liver, thyroid,pancreas, kidney, and mammary gland effects at the highest dosinglevel. As with isocyanates, DETDA presents a skin contact hazardand has an extremely low vapor pressure. It requires skinprotection and presents a particulate aerosol hazard only topersonnel directly exposed to the spray mist.

The solvent used in the sealant, PM Acetate, is watersoluble and will not cause defatting of the skin, a commonsolvent hazard. On the other hand, it has a unique, u.-pleasantodor which becomes noticeable between .1 and 1 ppm due to theacetate portion. The odor caused a "health awareness" problemwith the general hangar population. This is a new odor to them,and they believe they are being "overexposed" to this chemical.The manufacturer, Dow Chemical, has conducted animal testing andrecommends an exposure limit of 100 ppm. They note, however,that at concentrations of 80 ppm, no human would be able to standthe "terrible stench."

AIR SAMPLING STRATEGIES AND RESULTS

Many air samples were collected during the three differentsurveys. They were separated into three different categories tocoincide with the three different exposure groups.

First, breathing zone samples were collected on thepersonnel spraying the sealant in the tank. Next, breathing zonesamples and some general area samples were collected during thesealant mixing operation. Finally, general area samples werecollected at varying distances from the aircraft being sprayedrepresenting possible exposures to personnel not associated withthe sealant process.

Appendix B contains all the tabulated sample results alongwith the most stringent exposure guidelines. The 15-min TimeWeighted Average (TWA) values indicate worst-case exposuresassuming all the contaminant is collected in the first 15 minutesof the sampling period. These values are then compared to theShort Term Exposure Limit (STEL). Figures 2-7 show all thesampling locations utilized. Note that no data is available forthe sampling done by Lt Devine during September 1991.

Sample Results Within Tank

Solvent samples for the priming operation were onlycollected during the January 1991 survey. The hicýest exposureswere for isopropyl alcohol and toluene. Neither compound's 8-hrTWA exceeded the TLV; however, isopropyl alcohol exceeded a worstcase STEL by three times.

8

Sampling Point A4(top of aircraft) A2 Fuel Tank Entry Point

(under aircraft)

Sampling Point A3Sampling Point Al

A5 (mixer)A6 (sealer) Sealant Mixing Point

(inside fuel tank)

Sampling Point A2

NOTE: All sampling pointsapp. 17 ft fromentry point

Figure 2. Sampling Points of F-111 Aircraft (not to scale)22 Jan 91

9

Al Fuel Tank Entry Point

Sample Point Al (under aircraft)

Sample Point A3

A5 (sealer)(inside fuel tank)

Sealant Mixing Point

Sample oint A2

A4 (mixer)

NOTE: All sampling pointsapp. 17 ft fromentry point

Figure 3. Sampling Points of F-111 Aircraft (not to scale)

23 Jan 91

10

Sampling Point A2

F2 Fuel Tank Entry Point Sampling Point A4(top of aircraft)

Sampling Point A3Sampling Point Al

A5 (sealer)(inside fuel tank)

Sealant Mixing Point

Figure 4. Sampling Points of F-Ill Aircraft (not to scale)

24 Jan 91

U

Fuel Tank Entry Point

Sampling Point A2 (side of aircraft)

A6 (sealer) Sampling Point A4(inside fuel tank) (sprayers helper on stand

outside entry point)

S- Sampling Point A3

Sampling Point Al

Sealant Mixing PointA5 (mixer)

Figure 5. Sampling Points of F-111 Aircraft (not to scale)

25 Jan 91

12

Sampling Point 6

F1 Fuel Tank Entry Point(side of aircraft)

F2 Fuel Tank Entry Point Sampling Point 5(top of aircraft)

Sealant Mixing PointSampling Point 3/

Sampling Point 7 Sampling Point 9

A2 Fuel Tank Entry nt Sampling Point 8(under aircraft)

Sampling Point 2 Al Fuel Tank Entry Point(under aircraft)

Sampling Point 4

NOTE: Sample Point 1(sealer inside differentfuel tank each day)

Figure 6. Sampling Points of F-1l Aircraft (not to scale)12- 16 Aug 91

13

Sample Point D Sample Point C

Sealant Mixing Point

Sample Point E

Sample Point B

Sealant Spray Guns

Sample Point A

Figure 7. Sampling Points of F-il Aircraft (not to scale)30 Oct 91

14

Strontium chromate 8-hr TWA values exceeded the TLV by asmuch as 360 times during the January 1991 sampling and 680 timesduring the August 1991 sampling. It is important to note thatthe TLV for strontium chromate has changed since the survey wasdone. The TLV at the time of the sampling was 0.05 mg/m 3; thenew TLV is 0.0005 mg/m 3 . Consequently, not enough air volume wascollected during the sampling and the detection limit of theanalysis of these samples is above the TLV.

The August 1991 survey sample results indicate a worst caseHMDI exposure that exceeded the TLV by 10.3 times. The DETDA andlM2PA sample results are well below the manufacturer'srecommended exposure limits. Although some of the above resultsseem very high, they originate within a confined space andpersonnel are wearing a positive pressure supplied respiratorwhich provides a protection factor of 1000.

Sample Results From Mixing

Samples were collected on the mixer only during the Jan 91survey and all results were below recommended exposureguidelines. However, due to the extreme sensitizationcharacteristics of isocyanates and the close proximity to theongoing operation, all mixing personnel should continue to wearthe PPE previously described in the PPE section.

Bample Results Within Hangar

Sample collection points ranged from 13 to 120 feet from theaircraft being sprayed. During the January 1991 survey, severalstrontium chromate samples were above exposure limits. On 24January, levels exceeding the TLV by 18 times were detected inlocation A4 (see Figure 4). On 25 January, levels exceeding 100times the TLV were measured on the helper (see Figure 5). Duringthe August 1991 survey, all general area samples were belowdetection limits. However, as noted above, due to the low samplevolume collected, the TLV is below the analysis detection limit.These results indicate that, with the exception of strontiumchromate at location A4, no airborne hazard exists outside thefuel tanks. The levels of air samples collected by Lt Devine forDETDA and 1M2PA were below the manufacturer's recommendedexposure limits.

15

CONCLUSIONS

1. This process can be done efficiently and SAFELY!!

2. Odor does not mean there is a hazard!!

3. Exposures are classified into three differentcategories.

4. Exposures within the tank can be and are controlled withthe use of current PPE and ventilation.

5. Results conclusively indicate, excepting strontiumchromate, no exposures outside the tank.

RECOMMENDATIONS

1. Have a balanced tank ventilation system designed forthis process. It must include a Class 2 flameproof particulatefilter.

2. All accessible tank openings must be covered.

3. Keep the chemistry of the products consistent whenmixing. Changes in material viscosity can increase misting orclogging.

4. Keep the spray gun pressure constant. Increasedpressure will increase material misting.

5. PPE described in the process T.O. must always be worn.Do not deviate due to a shorter exposure duration. The helpermust wear the same PPE as the sealer to protect against strontiumchromate exposure.

6. When the proposed OSHA Confined Space Entry Rule becomesfinal, compliance is mandatory. Most of the requirements areadministrative and are described in the rules.

7. Provide employee training and hazard communication.

8. Ensure current sealant utilization rates do not violatethe current state regulations.

9. Fuel tanks should be monitored prior to entry and duringthe operation for oxygen and explosive levels.

10. SGPB should continue to conduct process surveys withair sampling at least annually.

16

APPENDIX A

VULCANIZATION MECHANISM

17

VULCANIZATION MECHANISM:

Reaction starts after Part A and B are mixed -

0

(A) R-C - C---R' (Epoxy-Thioether Resin)+

(B) H2N-<O>-R"-<O>-NH2 (Diamine)

H-O A --------------- ISOCYANATE CAN REACT

R-C - C-R'

HN-<O>-R-<O>-NH2 -------------

EPOXY CAN REACT

NOTE: Amine opens Epoxide ring generating hydroxyls (-OH) whichcan react with Isocyanates which can also react with Amines.

18

APPENDIX B

AIR SAMPLE RESULTS

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