SafetyBulletinU.S. Chemical Safety and Hazard Investigation Board

SODIUM HYDROSULFIDE: PREVENTING HARM

Introduction

Since 1971, reported incidents involving liquid solutions of sodiumhydrosulfide (NaHS) have resulted in 32 deaths and 176 injuries, most

notably in the leather tanning and pulp and paper industries. The mostserious safety concern associated with NaHS is its capacity to producelarge amounts of deadly hydrogen sulfide gas (H2S) when it reacts with anacid or is exposed to high heat.

Despite its pungent rotten egg odor, H2S can deaden the nerves that detectodors, thereby preventing those exposed from being able to smell life-threatening airborne concentrations. This condition is referred to as“olfactory fatigue” and must be considered when designing NaHS safetysystems.

This Safety Bulletin is published to increase awareness of the hazardsassociated with NaHS and to outline safety practices to minimize thepotential for harm to workers and the public.

No. 20 | 03-03-BJuly 2004

Defining theProblemNaHS releases highly toxic H2S ifmixed with an acid or if exposed toexcessive heat. Because it iscorrosive, it is also potentiallyharmful to the skin and eyes.1

NaHS incidents typically involvethe following three elements:

� An inadvertent spill, leak, ormixing, whereby NaHS reactswith an acidic solution toproduce H2S (Figure 1).

1 Although this bulletin addresses thehazards associated with NaHS solutions,its precautions also apply to othersulfide-containing substances (e.g.,sodium sulfide), which are often usedinterchangeably with NaHS, and whichalso generate H2S when mixed with acids.

Sodium Hydrosulfide

Common synonyms:

NaHS (NaSH) Sodium bisulfide Sodium sulfhydrate Sodium hydrogen sulfide Sodium mercaptan

CAS No.: 16721-80-5

UN No. (solution): 2922(Figure 2)

DOT Hazard Class: 8

EPA Hazardous Waste No.:D003

� Absent or inadequateengineering controls, such asventilation or H2S detectiondevices, coupled withinadequate PPE.

� Inappropriate emergencyresponse actions by workers andemergency responders.

This bulletin reviews selectedNaHS incidents that caused deathand injury, for example:

� Delivery drivers inadvertentlypumping NaHS into acidstorage tanks. (See WhitehallLeather, Horween Leather, andPrime Tanning case studies onpages 13–15.)

��Figure 1. Firefighters inNaHS and H2S protective gear.

MIT

2

CSB Safety Bulletins offer advisoryinformation on good practices formanaging chemical process hazards.Case studies provide supportinginformation. Safety Bulletins differfrom CSB Investigation Reports inthat they do not comprehensivelyreview all the causes of an incident.

U.S. Chemical Safety and HazardInvestigation Board

Office of Investigations and SafetyPrograms

2175 K Street NW, Suite 400Washington, DC 20037-1848202-261-7600www.csb.gov

� NaHS being allowed to mix withacids in a plant sewer system.(See Georgia-Pacific andWestvaco case studies on pages13-14.)

� Mixing of NaHS and an acidinside a common spillcontainment. (See PowellDuffryn case study on page 13.)

PhysicalCharacteristicsand Uses of NaHS

2 CSB compiled incident data and safetypractices described throughout thisSafety Bulletin during a comprehensivereview of NaHS incidents and industryhandling practices.3 Total U.S. production for all forms ofNaHS was approximately 269,000 tonsin 2003.

� Figure 2. Shippingplacard with UN numberand DOT hazard class.

CSB identified the following twocommon management failuresduring its review of catastrophicNaHS-related incidents:2

� Failure to identify and mitigatehazards during process systemdesign and engineering.

� Failure to manage hazards thatwere not controlled throughgood design and engineering.

Typical NaHS solutions are pro-duced commercially by combiningH2S with caustic soda (NaOH), asshown in the following reaction:

Table 1 summarizes the generalphysical properties of NaHSsolutions.

The resulting finished solution hasa pH of approximately 11.5.Depending on its solution strength(22 to 60 percent NaHS), it isheated to 71 to 82 ºC to preventcrystallization. NaHS is soldcommercially in both solution andflake forms, with solutionsaccounting for about 80 percent oftotal U.S. production.3

NaHS is used in a variety ofindustries (Figure 3):

� In the pulp and paper industry,to remove lignin from woodchips.

� In mining, as a flotation agent toseparate impurities.

� In manufacturing, as a rawmaterial or purifying agent.

� In the leather tanning industry,to remove hair from hides.

H2S NaOH

NaHS H2O+

+

�

Molecular weight: 56.1Specific gravity:

1.152 (a)–1.376 (b)

pH of solution:strongly alkaline (11–12)

Solution freezing point:-15ºC(a) – 40ºC

(b)

Odor: rotten eggH2S flammable limits

(% H2S in air):Lower: 4Upper: 44

(a) 22% solution.(b)

60% solution.

Table 1Physical Properties of NaHS

3

ACGIH: American Conference of GovernmentalIndustrial Hygienists

AIChE: American Institute of Chemical EngineersAIHA: American Industrial Hygiene AssociationANSI: American National Standards InstituteASSE: American Society of Safety EngineersATSDR: Agency for Toxic Substances and Disease

Registry, DHHSºC: Degrees CelsiusCAS: Chemical Abstracts ServiceCCPS: Center for Chemical Process Safety, AIChECDC: Centers for Disease Control and Prevention,

DHHSCFR: Code of Federal RegulationsCO2: Carbon dioxideCSB: U.S. Chemical Safety and Hazard Investigation

BoardDHHS: U.S. Department of Health and Human

ServicesDOE: U.S. Department of EnergyDOT: U.S. Department of TransportationEPA: U.S. Environmental Protection AgencyERPG: Emergency Response Planning Guidelines, AIHAH: HydrogenH2O: WaterH2S: Hydrogen sulfideHazCom: Hazard communication, OSHAIDLH: Immediately dangerous to life or health

MIT: Massachusetts Institute of TechnologyMSDS: Material safety data sheetNa: SodiumNaHS: Sodium hydrosulfideNaOH: Sodium hydroxideNAS: National Academy of SciencesNFPA: National Fire Protection AssociationNIOSH: National Institute for Occupational Safety and

Health, DHHSNLM: National Library of Medicine, National Institutes

of Health (NIH), DHHSNRC: National Response Center, USCGNTSB: National Transportation Safety BoardOSHA: Occupational Safety and Health Administration,

U.S. Department of LaborPEL: Permissible exposure limit, OSHApH: Potential of hydrogenPPE: Personal protective equipmentppm: Parts per millionPSM: Process safety management, OSHAPTFE: PolytetrafluorethyleneREL: Recommended exposure limit, NIOSHSCBA: Self-contained breathing apparatusSO2: Sulfur dioxideSTEL: Short-term exposure limitTWA: Time-weighted averageUN: United NationsUSCG: U.S. Coast Guard

��Figure 3. NaHS use by industry section.

Copper flotation 30%

Pulp & paper 42%

Miscellaneous 5%

Leather tanning 10%

Chemical & dyemanufacturing

13%

The Innovation Group

4

Concentration(ppm) Health Effects (a)

0.05 Rotten egg odor detectable by most humans.

0.13–30 Obvious and unpleasant odor.

50–150 Olfactory fatigue (temporary loss of smell) and markeddryness and irritation of nose and throat. Prolongedexposure may cause runny nose, cough, hoarseness,headache, nausea, shortness of breath, and severe lungdamage (pulmonary edema).

200–250 Worsening and more rapid onset of the above healtheffects; possible death in 4 to 8 hours.

300–500 Excitement, severe headache and dizziness, staggering,unconsciousness, and respiratory failure likely in 5minutes to 1 hour; possible death in 30 minutes to 4hours.

500+ Rapid onset of severe toxicity, respiratory paralysis, anddeath. If not fatal, may cause long-term effects such asmemory loss, paralysis of facial muscles, or nerve tissuedamage.

800–1,000 May be immediately fatal after one or more breaths,resulting in an instant unconsciousness or “knock-down”effect.

Table 2Inhalation of H2S

(a) Data from NIOSH, NLM, and ATSDR.

Health HazardSummaryBecause NaHS is corrosive, itpresents a hazard to unprotectedskin and eyes. However, its mostserious hazard is its propensity toproduce toxic H2S gas when mixedwith an acid or exposed to high heatsources such as a fire. The acidreaction chemistry is shown as:

Inhalation

The gases released by NaHS arecorrosive and may contain highlevels of H2S. Inhalation of H2S isirritating to the nose and throat.At higher concentrations, it canproduce olfactory fatigue, abuildup of fluid in the lungs(pulmonary edema), severeshortness of breath, and death.Table 2 outlines the health effects ofinhaling H2S.

Continuous exposure to lowconcentrations (5 to 10 ppm)of H2S or brief exposure tohigher concentrations (above50 ppm) deadens the odor-detecting nerves in the nose andlessens the ability to smelldangerous concentrations. Thehigher the concentration ofH2S, the faster the onset ofolfactory fatigue.

H2S exposures maycause olfactory fatigue

�

Eye Contact

Corrosivity hazardBecause of the high pH of NaHSsolutions (approximately 11.5),contact may severely irritate andburn the conjunctiva and cornea,4

and may result in permanent tissuedamage.

Hazard from generated H2SExposure to low concentrations ofH2S over several hours or days may

result in “gas eyes” or “sore eyes,”with symptoms of scratchiness,irritation, tearing, and burning.Symptoms are likely to disappearwhen the exposure ends. Pro-longed exposure to concentrationsof H2S above 50 ppm may causepermanent damage or intensetearing, blurring of vision, andpain when looking at bright light.

Skin Contact

Skin contact with NaHS mayproduce pain, irritation, redness(erythema), or burns. Becausesymptoms of exposure severity may

4 The conjunctiva and cornea are the thin,transparent tissues that cover the outersurfaces of the eye.

NaHS Acid (H+)

Na+ H2S+

+

�

5

be delayed, affected skin should betreated immediately. (See the firstaid guidance on page 12.)

Ingestion

Ingesting a small amount of NaHSin a single dose will likely produceonly minor throat irritation orburning of the esophagus.Ingesting a larger quantity,however—or small quantities overan extended period—may seriouslydamage the gastrointestinal tract.In addition, NaHS that mixes withstomach acids produces H2S andmay cause the health effects asso-ciated with inhalation (Table 2).

Incident DataFrom reported data for the UnitedStates from 1971 through 2003, CSBidentified 45 NaHS-relatedincidents (Figure 4).5 Collectively,these incidents resulted in:

� 32 fatalities.

� 176 injuries.

� 351 medical evaluations.

� At least 10 plant or communityevacuations.

��Figure 4. NaHS incidents* by industry sector.

Thirty-six of the incidents resultedfrom H2S releases, and the remain-der from skin or eye exposure.

The following categories ofincidents were identified duringthis review:

� Improper mixing or transfer: 15(33 percent).

� Spills: 12 (27 percent).

� Mechanical failure: 7 (16percent).

� Improper maintenance or repair:6 (13 percent).

Five of the 45 incidents (11 percent)were attributed to unknowncauses.

Incident data were obtained fromOSHA, EPA, and ATSDRdatabases, as well as industryquestionnaires, interviews, andmedia sources. Only thoseincidents that were reported andaccessible are represented.

Although the incidents reviewedare not all-inclusive, their numberand severity clearly indicate thatNaHS presents a serious hazard inthe workplace.

Prevent HarmGood safety management includesidentifying and evaluating hazardsduring initial process planningand design, and continuesthroughout the life cycle of theoperation—both for new processesand for modifications. Thisapproach allows managers andemployees to understand andaddress hazards prior to startup.

Hazard control measures such aswork practice controls and PPE aresecondary layers of protection.They should be considered onlyafter attempting to eliminatehazards through design andengineering, or when substituting

5 The earliest recorded NaHS incidentidentified during the CSB reviewoccurred in 1971. Regulatory reportingrequirements and industry usagepractices have changed significantlysince that time, which may account forincident rate fluctuations among thevarious industry sectors. For example,nearly all of the leather tanningincidents occurred between 1971 and1990, and no transportation incidentswere reported prior to 1990. Theincidents CSB reviewed include pulpingliquor incidents in which NaHS wasused as the sulfide source.

Pulp & paper 14%

Transportation 12%

Manufacturing 6%

Other 6%

Refining 1%

Unknown 1%

Leather tanning 5%

*An “incident” is a NaHS-related event involving afatality, injury, medical evaluation, or evacuation.

6

for a less hazardous material orprocess is impractical.

A multidisciplinary team applyingestablished process safetymanagement principles shouldidentify and evaluate hazards.These principles are outlined in theOSHA Process Safety Managementof Highly Hazardous Chemicals(PSM) Standard and in CCPSpublications listed at the end ofthis bulletin.

The PSM Standard regulatesprocesses containing thresholdquantities of highly hazardouschemicals, explosives, andflammable liquids in amountsexceeding 10,000 pounds. 6 NaHSis not a PSM-covered chemicalbecause—despite its reactivepotential to produce large amountsof H2S when mixed with acids orwhen exposed to heat—it does notmeet the OSHA listing criteria.

CSB has recommended that OSHAexpand PSM to include chemicalswith reactive characteristics similarto those exhibited by NaHS (i.e.,relatively stable chemicals thatreact dangerously with othersubstances).7 (See the CSB Hazard

Investigation Report, ImprovingReactive Hazard Management (2002;www.csb.gov).

Design to EliminateHazards

Process systems must be designedto prevent NaHS from inadver-tently mixing with acidic solutions.The potential for human errorduring handling should beidentified and eliminated to themaximum extent practicable.

Interviews and literature reviewswith NaHS manufacturers, tradeassociations, and industryrepresentatives highlighted thefollowing design practices:

� Always treat sewers asextensions of the process. DoNOT add wastes withoutanalyzing for compatibility withother sewer contents.

� Separate acid- and NaHS-containing waste streams, ordesign the system to handlemixing so as to prevent anuncontrolled or otherwisehazardous release of H2S.

� Construct separate containmentsfor NaHS and acid storagecontainers and processequipment.

� Install waste-stream/sewermonitors with alarms to warnemployees of system upsets orunfavorable acid conditions.

� Install ventilation systems andH2S detectors and alarms atlocations where hazardousconcentrations may occur.

� Design storage tank vents tominimize the potential forworker exposure.

� Design transfer connections andprocedures to prevent inadver-tent mixing. Limit access tothese connections to trained andauthorized personnel throughreliable and effective controls,which should includeprocedures and physical barriers(e.g., locking devices or uniquefitting configurations).

� Construct process systemcomponents from materialscapable of withstanding thecorrosivity and temperaturesassociated with NaHS solutions.NaHS manufacturersrecommend the followingmaterials:8

� Storage tanks and steamcoils: 304 stainless steel.

� Pumps: 304L or 316Lstainless steel.

� Packing: PTFE-impregnatedcarbon fiber.

� Piping: 304L stainless steel,insulated and heat-traced inlocations where freezing mayoccur.

� Gaskets: Spiral-wound 316Lstainless steel or a PTFE ring.

� Plug valves: Lubricated ormade with a PTFE sleeve andseal.

6 See 29 CFR 1910.119 at www.osha.gov/SLTC/processsafetymanagement/.Highly hazardous chemicals are listed inAppendix A.7 Based on their reactive characteristics,the chemicals included in Appendix Awere selected from the 1975 version ofNFPA 49, Hazardous Chemical Data.OSHA selected only those chemicals withinstability ratings of “3” or “4” (on ascale of 0 to 4). These ratings focuspurely on the chemicals themselves anddo not consider the consequences ofmixing with other chemicals.

8 This information illustrates the types ofmaterials manufacturers recommend foruse in NaHS process systems. It is notintended as a substitute for recognizedand generally accepted good engineeringpractices for the specific facility design,construction, or maintenance.

7

Manage Hazards

Eliminating hazards throughprocess design and engineering isthe optimal hazard managementsystem. However, additionalsystems are required when designand engineering do not eliminatethese hazards. CSB identified thefollowing management systems asparticularly applicable to NaHSusers.9

Communicate hazards toemployees

The OSHA HazCom Standard (29CFR 1910.1200) is based on thesimple concept that employeeshave both a need and a right toknow of the hazards associatedwith chemicals to which they areexposed. They also need to know

how to protect themselves fromadverse health effects due tochemical exposure. The generalrequirements of this standard areoutlined at www.osha.gov.

The HazCom requirementspertaining to NaHS MSDSs andH2S training are outlined below:

� MSDSs: Employers are requiredto obtain an MSDS for eachhazardous chemical (present orproduced at the facility) and tomake them readily available toworkers. The informationcontained in MSDSs may varysignificantly among NaHSmanufacturers.10 Operations andsafety personnel should,therefore, attempt to acquire abetter understanding of NaHShazards through such resourcesas this Safety Bulletin, MSDSsand product information frommultiple NaHS manufacturers,and databases such as the NLMHazardous Substance DataBase.11

� Training: Employers arerequired to train their employeesand inform contractors(including delivery drivers,construction workers, andemergency responders) of site-specific NaHS and H2S hazards,including plant hazard labelingsystems and locations ofMSDSs.12 This is often

9 The safety programs outlined in this

section relate to circumstances identifiedin the incidents CSB reviewed. Otherrelevant safety programs—such asmanagement of process change, linebreaking, lockout/tagout, and processand equipment integrity—are alsoextremely important components of asuccessful accident prevention program.

10 See www.csb.gov and www.osha.govfor discussions of MSDS inconsistenciesand inaccuracies.11 toxnet.nlm.nih.gov/index.html.12 See Safety Requirements for H2S TrainingCriteria (ANSI Z390.1-1995, available atwebstore.ansi.org/ansidocstore/default.asp) for a model H2S trainingprogram.

accomplished in the form of afacility safety orientation.

Provide personal protectiveequipment

Facilities should rely on PPE onlyafter conducting a hazardassessment, as required by theOSHA Personal ProtectiveEquipment, General RequirementsStandard (29 CFR 1910.132).13

Employees should participate inthe selection of PPE because of thepotential for stress and discomfortcreated by restrictions to move-ment, vision, and dexterity. Wherepractical, PPE should be simple tooperate and reasonablycomfortable to wear for theduration of the exposure.

� Chemical protective clothing:PPE required to protect workersfrom the corrosive hazardsassociated with NaHS includeseye and face protection, chemicalprotective gloves, protectiveclothing, and foot protection(www.cdc.gov/niosh).

� Respiratory protection: Becauseof the toxicity and potential forolfactory fatigue associated withH2S (see Table 3), extendedexposure above any of the OSHAPELs14 requires use of an SCBAor airline respirator equippedwith a full-face piece andoperated in pressure-demand or

13 www.osha.gov/SLTC/personalprotectiveequipment/.14 See Table Z-2, 29 CFR 1910.1000,www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9991.

H2S hazard: separateNaHS and acids

Allowing spilled NaHS toinadvertently mix with an acid(pH < 7) poses a significant riskof harm. Similarly, if a sewersystem is not designed to controlH2S, allowing NaHS to run off toa sewer containing acids alsoposes a significant risk. Largeamounts of toxic (and flammable)H2S may evolve very rapidly!

�

8

positive-pressure mode. Suchrespiratory protection could berequired when transferringmaterials to or from tankers,cleaning process equipment,responding to NaHS releases,and performing emergencyrescue.

According to OSHA, employersare responsible for determiningexposure for all employeeactivities, including thosethat expose contractors and

rugged and reliable, simpler tooperate, and much less expen-sive. Examples of availabledevices are noted below:

� Personal H2S detectors withaudible, vibrating, andvisual alarms: Thesedetectors can be clipped intoa shirt pocket or worn on ahard hat. They are relativelyinexpensive and reliable,and have low-maintenanceelectrochemical sensors andlong-lasting batteries.

� Stationary H2S detection andnotification systems: Thesesystems provide alarmnotification 24 hours a dayand can be used to auto-matically notify emergencyresponders. Freestandingsolar- and battery-poweredsystems are also availablethat can be equipped withradio transmitters to sendreal-time monitoring resultsto a remote alarm or warningdevice.

Enter confined spaces safely

Because H2S is heavier than air, ittends to concentrate near or belowground level, especially wherethere is limited air movement.Sump pits, storage and processtanks, valve trenches, and sewersare particularly susceptible to highconcentrations of H2S and mayrequire atmospheric testing,communications equipment, andstandby emergency rescuepersonnel.

OSHA regulates confined spaces inthe Permit-Required Confined

15 A person trained in industrial hygienesampling practices must performexposure monitoring to ensurecompliance with the OSHA PEL.16 www.osha.gov/SLTC/respiratoryprotection/).17 OSHA relies on NIOSH as the testingand certifying body in 29 CFR 1910.134.NIOSH requires end-of-service lifeindicators for filters used to protectagainst chemicals with poor warningproperties, such as H2S. There arecurrently no approved filters for extendedprotection against H2S.

OSHA (PEL)Ceiling

(a) 20 ppm

10-minute peak (b) 50 ppm

8-hour TWA 10 ppm

NIOSHIDLH

(c) 100 ppm

REL(10-minute ceiling)

(d) 10 ppm

ACGIH15-minute STEL

(e) 15 ppm

8-hour TWA 10 ppm

(a) Concentration generally not to beexceeded during the work shift.

(b) Workers may be exposed above theceiling level up to this concentrationfor a maximum of 10 minutes.

(c) Exposure to environments exceedingthese airborne concentrations is likelyto cause death or permanent adversehealth effects or to prevent escape.Use of SCBA in pressure-demand orpositive-pressure mode is required(see 29 CFR 1910.134).

(d) Exposure should not exceed the RELfor any continuous 10-minute periodduring the work shift.

(e) According to ACGIH, exposureshould not exceed this level for anycontinuous 15-minute period duringthe work shift.

Table 3H2S Exposure Limits

visitors.15 If respiratoryprotection is required, employersmust comply with the OSHARespiratory Protection Standard(29 CFR 1910.134).16

Before relying on respirators,facilities must have determinedthat it is impractical to eliminateor control hazards throughsubstitution of a less hazardouschemical, design andengineering controls, or workpractice or administrativecontrols.

NIOSH has certified certain full-face air purifying respirators (i.e.,a facemask equipped with afilter) for emergency escapepurposes, but only where H2Sconcentrations do not exceed 100ppm.17 For all other situations,NIOSH prescribes supplied-airrespirators. These requirementsare outlined in the NIOSH PocketGuide to Chemical Hazards (2003;www.cdc.gov/niosh/npg/npg.html).

� Air monitoring for H2S: Inenvironments that are normallysafe, but which pose the risk ofhazardous H2S exposure, theonly way to ensure worker safetyis to continuously monitor theair. In recent years, H2S monitorshave become much smaller, more

9

Spaces Standard (29 CFR1910.146).18 Further informationand guidance on this standard isprovided in the references sectionof this bulletin.

Handle and store NaHS safely

The hazards associated with NaHSrequire employers to establishfacility-specific safe handling andstorage practices and proceduresfor both employees and contractors.These practices and proceduresinclude:

� Controlling access andsupervising product deliveryand transfer.

� Installing local exhaustventilation on process or storageequipment where personnelexposure is likely and ensuringthat such systems are operatingproperly before starting aprocess.

� Installing fixed H2S monitorswith alarms in NaHS storageand offloading areas whereconcentrations could exceed safelevels.

� Providing PPE and emergencyeyewash and shower facilitieswhere there is a risk of exposureto NaHS.

� Ensuring that NaHS-containingwastes are not flushed to acid-containing sewers withoutcontrols to prevent a release ofH2S.

� Storing NaHS separately fromlow pH (acidic) materials toavoid inadvertent mixing.

� Decide whether to evacuate orshelter-in-place: This decisionis made under urgent conditions.Factors that must be consideredinclude population distribution,risk of exposure, adequacy ofavailable shelters, evacuationtime requirements, and otherfactors such as the charac-teristics of the chemical releasedand weather conditions. Thisissue has been studiedthoroughly by researchers at theOak Ridge National Laboratory,as documented in PlanningProtective Action Decision-Making:Evacuate or Shelter-in-Place?(USDOE, 2002; www.osti.gov/bridge/).

A decision to evacuate should bebased on the reasonableassurance that movement is inthe best interest of those beingevacuated:

� Evacuation: Downwind of arelease—before starting tomove upwind—unprotectedpersonnel should movedirectly crosswind to one-half of the downwinddistance from the spill. Thecrosswind distance varies inrelation to the size of the spilland downwind distance.See Figure 5 and Table 4 forthe initial isolation andprotective action distancesrecommended by the DOTEmergency ResponseGuidebook (2000;hazmat.dot.gov/gydebook.htm).

� Clearly labeling NaHS con-tainers, process piping, andcritical process piping valvesthat may contain NaHS withessential hazard information.

� Warning against exposure ofNaHS to excessive heat orstorage near open flames or otherignition sources that mightgenerate or ignite flammable H2S.

� Ensuring that storage containersand process equipment materialsare compatible with thealkalinity of NaHS. Manu-facturers of NaHS warn againstusing copper, zinc, or aluminum.

� Implementing an emergencynotification system to informemergency responders andpotentially impacted offsiteresidents of threateningincidents.

EmergencyResponseEmergency responders mustimmediately take precautions inthe case of a fire or spill involvingNaHS. If there is evidence of anH2S release—either the presence ofits characteristic rotten egg odor oraffirmative H2S monitoringresults—emergency respondersshould:

� Restrict access to the spill/release site: Allow onlyemergency personnel equippedwith proper PPE to enter the area(i.e., NIOSH-approved, full face-piece SCBA in pressure demandmode, and protective outergarments).

18 www.osha.gov/SLTC/confinedspaces/

10

� Shelter-in-place: This is aprecaution to keep peoplesafe while remainingindoors. It calls for takingrefuge in a preferably small,interior room with no or fewwindows; closing windowsand doors; turning offheating and air-conditioningsystems; and listening tolocal TV/radio for emer-gency response directions.

Offsite residents or plantpersonnel who may berequired to shelter-in-placemust be provided withinstructions and training,and must have necessarysupplies on hand (e.g., food,water, tape, vinyl sheeting)prior to an incident. Detailed 19 NAS has developed acute exposure

guideline levels that may be moreprotective than AIHA ERPGs. Interimexposure levels for H2S are available atwww.epa.gov/oppt/aegl/.

��Figure 5. Initial isolation and evacuation diagram.

information regardingshelter-in-place is availableat www.cdc.gov/ andwww.redcross.org/.

� Conduct continuous downwindmonitoring: Determine if H2Sconcentrations exceed the AIHAERPGs19 (ERPG–3 or –2 valuesfrom Table 5) or the OSHA PEL;and continue to evacuate orshelter-in-place as required.

Firefighting

Contact between NaHS and anacid—or exposure to excessiveheat—liberates H2S, whichpresents an inhalation and fire

Small Spill (a)

1. Isolate spill area 100 feet inall directions

2. Protect persons downwind

Day (b) – 0.1 mile (528 feet)

Night – 0.2 mile (1,056 feet)

Large Spill (c)

1. Isolate spill area 700 feet inall directions

2. Protect persons downwind

Day (b) – 0.9 mile (4,752 feet)

Night – 2.7 miles (14,256 feet)

(a) From a small package (55 gallons orsmaller) or a small leak from a largepackage.

(b) Sunrise to sunset.(c) From a large package or from many

small packages.

Source: USDOT, 2000.

Table 4H2S Initial Isolation

and Protective ActionDistances

Downwind distance from spill

Wind direction

Spill/release

Initial isolationzone

1/2Downwind

distance

1/2Downwind

distance

11

hazard. In addition, burning H2Sproduces sulfur dioxide (SO2),which is a severe respiratoryirritant that can be life threatening.If a fire involves NaHS, the DOTEmergency Response Guidebook(2000) recommends the following:20

� Small fires:

� Use dry chemicals, CO2, or

water spray.21

� Large fires:

� Use dry chemicals, CO2,alcohol-resistant foam, orwater spray.

� Move containers of NaHSfrom fire area if possible todo so without risk.

� Contain contaminated firecontrol water for laterdisposal.

� Fires involving a tank, railcar, ortank truck:

� Fight the fire from themaximum distance possible,or use unmanned hoseholders or monitor nozzles.

� Do NOT allow water to entercontainers of NaHS.

� Cool containers withflooding amounts of wateruntil well after the fire isextinguished.

� Withdraw immediately incase of a rising sound fromventing safety devices ordiscoloration of the tank.

� ALWAYS stay away fromburning tanks.

Spill Response

In the event of a NaHS spill:

� Do NOT allow NaHS to come incontact with acids.

� Contain the spill. Do NOT flushto a sewer unless the sewer isdesigned and engineered to con-trol the H2S that may be released.

� Remove sources of ignition sothat any H2S released will notignite.

� Provide maximum ventilation.

� Recover spilled material onadsorbents, such as sand orvermiculite, and place in coveredcontainers for reclamation ordisposal.

� For spills that exceed the 5,000-pound reporting threshold,22

22 NaHS is listed in Table 302.4 of the

Superfund, Emergency Planning andCommunity Right-to-Know Act (40 CFR302) as a hazardous substance with areportable quantity of 5,000 pounds,based on 100 percent purity (approxi-mately 1,077 gallons of 43 percentsolution). See www.epa.gov/swercepp/factsheets/epcra.pdf for moreinformation.

20 See Guide 154 for NaHS.21 Some manufacturers and fire safetyprofessionals caution against usingextinguishers containing CO2

and dry

chemical extinguishing media becausethey form acids when mixed with waterand may exacerbate the generation of H2Swhen used on fires involving NaHS.They recommend using water in floodingquantities to fight the actual fire, andwater spray or foam to control vapors.If CO2 or dry chemical extinguishers areused, responders must wear properrespiratory protection (i.e., SCBA).

60-MinuteConcentration(ppm)

ERPG–3 (a) 100

ERPG–2 (b) 30

ERPG–1 (c) 0.1

(a) ERPG–3 is the maximum airborneconcentration below which it isbelieved that nearly all individuals couldbe exposed for up to 1 hour withoutexperiencing or developing life-threatening health effects.

(b) ERPG–2 is the maximum airborneconcentration below which it isbelieved that nearly all individuals couldbe exposed for up to 1 hour withoutexperiencing or developing irreversibleor other serious health effects orsymptoms that could impair theirability to take protective action.

(c) ERPG–1 is the maximum airborneconcentration below which it isbelieved that nearly all individuals couldbe exposed for up to 1 hour withoutexperiencing other than mild transientadverse health effects or perceiving aclearly defined objectionable odor.

Source: AIHA, 1991.

Table 5H2S Emergency Response

Planning Guidelines

12

notify NRC at 1-800-424-8802 orwww.nrc.uscg.mil.23

Emergency Responders

Emergency responders must wearNIOSH-approved, full face-pieceSCBA in pressure-demand orpositive-pressure mode andchemical-resistant outer garmentswhen there is a threat of airborneconcentrations of H2S exceedingthe PEL. To avoid endangeringemergency responders, NaHS- orH2S-contaminated outerwearshould be discarded and victimsdecon-taminated prior to placingthem in a confined space, such as amedical transport vehicle.

First AidEach year a large number offatalities result from failed rescueattempts by those who rush intodangerous environments to helpfallen workers. First responders andemergency medical personnel mustprotect themselves before rendering aidto others.

24 Eight contractor employees wereinjured during the Georgia-Pacificincident when they remained in the zoneof danger to assist with the rescue offallen workers.25 In some states, administering oxygenrequires emergency medical certification.

Chemical shower and eyewashfacilities must meet the require-ments outlined in the OSHAMedical Services and First AidStandard (29 CFR 1910.151(c)).26

Applying elements of theEmergency Eyewash and ShowerEquipment standard, ANSI Z358.1-2004, fulfills OSHA requirementsand provides adequate protectionto workers.27

Skin Contact

Immediately remove contaminatedclothes and irrigate exposed skinwith copious amounts of water forat least 15 minutes, regardless ofsymptoms. A physician may needto examine the exposed area ifirritation or pain persists orworsens.

Ingestion

Do NOT induce vomiting orattempt to neutralize ingestedNaHS. Immediately requestemergency medical assistance bycalling 911 and the national PoisonControl Center emergency hotlineat 1-800-222-1222.

26 www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9806.27 ANSI Z358.1-2004 is available forpurchase at webstore.ansi.org/ansidocstore/default.asp.

Emergency rescue

If H2S is present, do NOTattempt to rescue a fallen workerwithout proper PPE.

�

Emergency responders responsiblefor facilities that handle NaHSshould familiarize themselves withthe ATSDR Medical ManagementGuidelines for H2S (2003;www.atsdr.cdc.gov/MHMI/mmg114.html). Do NOT enter anunknown or potentially hazardousenviron-ment without ensuringthat it is safe by sampling the airand/or wearing proper PPE.24

Inhalation of H2S

Move the victim into fresh air andadminister oxygen as necessary.25

Victims of overexposure to H2S (orNaHS vapors that may containH2S) should immediately receiveemergency medical attention.

Eye Contact

In the event of eye contact witheither NaHS or high concen-trations of H2S, immediatelyirrigate the eyes with copiousamounts of water for at least 20minutes, or until the arrival ofemergency medical personnel. Anophthalmologic examinationshould be conducted as soon aspossible because the extent of someinjuries related to corrosive eyeexposure may not be apparent for48 to 72 hours.

23 This is a regulatory threshold reportingquantity established by EPA with anemphasis on identifying adverse environ-mental impact. Spills and releases ofmuch smaller quantities of NaHS canlead to catastrophic consequences. Forexample, the spillage of about 100gallons of NaHS led to the Georgia-Pacific incident, reviewed on page 13.

13

Whitehall Leather Company,Whitehall, Michigan(1 killed, 1 injured)

On June 4,1999, thedriver of atanker truckfilled withNaHSinadvertentlypumped thetanker contentsinto a storagetank partiallyfilled with“pickle acid”(hydrochloricacid). Thetanker truckhad arrived atthe plantduring thenight shift.

The shift supervisor—never havingreceived a shipment of NaHS andbelieving it to be pickle acid—directed the driver to unload it intoa pickle acid storage tank (Figure6). The resulting reaction releasedH2S, which killed the driver andinjured a plant employee.

Powell Duffryn terminal fire,Savannah, Georgia(337 medical evaluations,community evacuation)

On April 10, 1995, the force from anexplosion in a solvent storage tankfractured NaHS transfer piping.Up to 300,000 gallons of NaHSspilled and mixed with a similarlylarge quantity of acidic cleaningsolution (Figure 7). The NaHS and

28 CSB investigators estimated that 100

gallons of NaHS was allowed toaccumulate in the pit.

Selected CaseStudiesGeorgia-Pacific, Naheola pulpand paper mill, Pennington,Alabama (2 killed, 8 injured)

On January 16, 2002, two workerswere killed and eight injured whileperforming maintenance near aNaHS transfer terminal. NaHShad recently been pumped from 15tanker trucks into storage tanks.Because of a leaking pump, NaHSaccumulated in a containment pitthat was connected to the plantacid sewer.

When the containment pit wasdrained, a relatively small quantityof NaHS28 reacted with acid in thesewer to produce H2S. The H2Sleaked through a faulty manwaycover seal into the area where thecontractors were working.

The CSB investigation concludedthat Georgia-Pacific managementwas unaware that the containmentpit drained to the acid sewer.However, neither Georgia-Pacificnor the previous plant owners hadadequately evaluated the potentialfor hazardous chemical mixing inthe sewer system and the release ofdeadly amounts of H2S.Consequently, plant personnel,contract workers, and emergencyresponders were unaware of andunprepared for the dangers.

�� Figure 6. Whitehall Leather offloading area.NTSB

acid solution tanks were colocatedinside an earthen containment.

The reaction released an enormousvolume of H2S, which caused 337people to seek medical evaluationsand forced 2,000 downwindresidents to evacuate. Theevacuation lasted more than 30days as H2S continued to evolvefrom NaHS-saturated soil.

This incident illustrates the failureof management systems to identifyand evaluate the hazards asso-ciated with colocatingincompatible materials inside asingle spill containment. The EPAinvestigation report (1998) isavailable at yosemite.epa.gov/opa/admpress.nsf/0/8e314f057b62e118852565fe006fa986?OpenDocument.

14

Stone Savannah River pulp andpaper mill, Wentworth,Georgia (1 killed, 4 injured)

On December 8, 1990, one workerwas killed and four injured when alarge quantity of H2S formedduring acid cleaning of a 20,000-gallon pulping solution pressurefilter. H2S was routinely producedinside the process vessel when thecleaning solution was used todissolve NaHS-containing pulpingfiltrate. Local exhaust ventilationnormally controlled the H2S.

However, on the day of thisincident, H2S leaked from thesystem and accumulated inside thewalled containment where workerswere operating valves. Accordingto witnesses, the workers imme-diately smelled H2S and tried toescape, but were overwhelmedbefore being able to climb out of thevalve pit. This incident highlights

��Figure 7. Powell Duffryn fire.

the dense gas properties of H2S andthe atmospheric hazards that maybe present in confined spaces.

WESTVACO paper mill,Covington, Virginia(10 injured)

On May 4, 1988, 10 employees werehospitalized for H2S exposurewhen a 300,000-gallon storage tankcontaining pulping solution

��Figure 8. WESTVACO paper mill tank failure.

collapsed (Figure 8). The plantsewer system routinely controlledstorm runoff, spills, anddischarged wastes.

However, when the NaHS-containing pulping solutionentered the sewer, it reacted withwaste acids and produced H2S—which escaped via drains, vents,and manways. The 10 injuredemployees were working at variouslocations near the vents andmanways.

Horween Leather Company,Chicago, Illinois(8 killed, 43 injured)

On February 14, 1978, eightworkers were killed, 43 wereinjured, and 57 sought medicalevaluation after being over-whelmed by H2S. The incidentbegan when a substitute deliverydriver unloaded a tanker truck ofNaHS into a storage tankcontaining an acid. He wasunfamiliar with plant operationsand NaHS hazards, and wasunsupervised by plant personnel.

EPA

Crawford Akers Photography

15

A large volume of H2S wasimmediately generated, which ledto evacuation of the entire plantand surrounding community.Although the tank fill line couplingwas designed to prevent inadver-tent mixing, the driver created amakeshift coupling when he wasunable to attach the line from thetruck.

Prime Tanning Company,Berwick, Maine (6 killed)

On April 2, 1971, six workers diedwhen NaHS was inadvertentlypumped into a tank containingacidic chrome tanning liquor,which has a pH of 3 to 4. TheNaHS delivery drivers had beeninstructed where to offload theirtanker truck.

When the drivers discovered thatthe truck’s fill nozzle would not fitthe tank’s coupler, they used anadapter nozzle. There was nolabeling on the tank to identify itscontents or to warn of the potentialhazard. Approximately 160gallons of NaHS had beentransferred to the tank before one ofthe drivers noticed that workersinside the plant were collapsing.NaHS had mixed with the chromeliquor to produce H2S.

References andAdditionalInformationANSI/ASSE, 2003. Safety

Requirements for Confined Spaces,Z117.1–2003 (webstore.ansi.org/ansidocstore/default.asp).

ANSI/ASSE, 1998. EmergencyEyewash and Shower Equipment,Z358.1-1998.

ANSI/ASSE, 1995. SafetyRequirements for H2S TrainingCriteria, Z390.1-1995.

ATSDR, 2003. Medical ManagementGuidelines for Hydrogen SulfideGas, August 2003(www.atsdr.cdc.gov/MHMI/mmg114.html).

ATSDR, 1999. Toxicological Profilefor Hydrogen Sulfide.

Bretherick, Leslie, P. G. Urben, andMartin J. Pitt, 1999. Bretherick’sHandbook of Reactive ChemicalHazards, Sixth Edition, Vol. 1,Butterworth-Heinemann.

CCPS, 2003. Essential Practices forManaging Chemical ReactiveHazards, AIChE(www.aiche.org).

CCPS, 1996. Inherently SaferChemical Processes, A Life CycleApproach, AIChE.

CCPS, 1994. Guidelines forPreventing Human Error in ProcessSafety, AIChE.

CCPS, 1992. Guidelines for HazardEvaluation Procedures, AIChE.

CCPS, 1989. Guidelines for TechnicalManagement of Chemical ProcessSafety, AIChE.

Health and Safety Executive (HSE),2000. Designing and OperatingSafe Chemical Reaction Processes,Norwich, U.K.: HSE Books.

McManus, Neil, 1999. Safety andHealth in Confined Spaces, LewisPublishers/CRC Press.

NFPA, 1975. Hazardous ChemicalData, NFPA 49.

NIOSH, 2003. Recommendations forChemical Protective Clothing, ACompanion to the NIOSH PocketGuide to Chemical Hazards, TableH, August 2003 (www.cdc.gov/niosh/npg/npg.html).

NLM Hazardous Substance DataBase (toxnet.nlm.nih.gov/index.html).

OSHA, 1993. Selected occupationalfatalities related to pulp, paperand paperboard mills as found inOSHA fatality/catastropheinvestigations, June 1993(www.osha.gov).

Rekus, John F., 1994. CompleteConfined Spaces Handbook, LewisPublishers/CRC Press.

Sayers, Robert H., 1979. “Safety inHandling and Using Sulfide,Sulfhydrate, and OtherHazardous Chemicals in aTannery,” Journal of AmericanLeather Chemists Association,Vol. 74, pp. 64–69.

16

Shih, Thomas, et al., 1967.“Hydrogen Sulfide Vapor—Liquid Equilibrium in AqueousSystems as a Function ofTemperature and pH,” TAPPIJournal, Vol. 50, No. 12, pp. 630–634, December 1967.

The Innovation Group, 2003.Chemical Profiles (www.the-innovation-group.com).

USCG, 2001. Chemical HazardsResponse Information System(CHRIS;www.chrismanual.com).

USCSB, 2003. Investigation Report,Hydrogen Sulfide Poisoning,Georgia-Pacific Naheola Mill,Pennington, Alabama, January 16,2002, Report No. 2002-01-I-AL,January 2003 (www.csb.gov).

USCSB, 2002. Hazard Investigation,Improving Reactive HazardManagement, Report No. 2001-01-H, December 2002

USDOE/Oak Ridge NationalLaboratory, 2002. PlanningProtective Action Decision-Making:Evacuate or Shelter-in-Place?ORNL/TM-2002-144, preparedfor Federal EmergencyManagement Agency(www.otsi.gov/bridge/).

USDOT, 2000. North AmericanEmergency Response Guidebook,J. J. Keller and Associates(hazmat.dot.gov/gydebook.htm).

USEPA, 1998. EPA ChemicalAccident Investigation Report,Powell Duffryn Terminals, Inc.,Savannah, Georgia, Office of SolidWaste and Emergency Response,EPA 550-R-98-003, May 1998(yosemite.epa.gov/opa/admpress.nsf/0/8e314f057b62e118852565fe006fa986?OpenDocument).

The U.S. Chemical Safety and Hazard Investigation Board (CSB) is an independent Federal agency whose mission isto ensure the safety of workers, the public, and the environment by investigating and preventing chemical incidents.CSB is a scientific investigative organization; it is not an enforcement or regulatory body. Established by the CleanAir Act Amendments of 1990, CSB is responsible for determining the root and contributing causes of accidents,issuing safety recommendations, studying chemical safety issues, and evaluating the effectiveness of other governmentagencies involved in chemical safety.

No part of the conclusions, findings, or recommendations of CSB relating to any chemical incident may be admittedas evidence or used in any action or suit for damages arising out of any matter mentioned in an investigation report(see 42 U.S.C. § 7412(r)(6)(G)). CSB makes public its actions and decisions through investigation reports, summaryreports, safety bulletins, safety recommendations, case studies, incident digests, special technical publications, andstatistical reviews. More information about CSB may be found at www.csb.gov.

CSB investigation reports may be purchased from:

National Technical Information Service5285 Port Royal RoadSpringfield, VA 22161-0001(800) 553-NTIS or (703) 487-4600Email: info@ntis.fedworld.govFor international orders, see:www.ntis.gov/support/cooperat.htm.

CSB publications may be downloaded at www.csb.gov orobtained by contacting:

U.S. Chemical Safety and Hazard Investigation BoardOffice of Government, Public, and Board Affairs2175 K Street NW, Suite 400Washington, DC 20037-1848(202) 261-7600