Safety

Bulletin

U.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 most

serious safety concern associated with NaHS is its capacity to produce

large amounts of deadly hydrogen sulfide gas (H2S) when it reacts with an

acid or is exposed to high heat.

Despite its pungent rotten egg odor, H2S can deaden the nerves that detect

odors, thereby preventing those exposed from being able to smell lifethreatening airborne concentrations. This condition is referred to as

“olfactory fatigue” and must be considered when designing NaHS safety

systems.

This Safety Bulletin is published to increase awareness of the hazards

associated with NaHS and to outline safety practices to minimize the

potential for harm to workers and the public.

No. 20 | 03-03-B

July 2004

Defining the

Problem

NaHS releases highly toxic H2S if

mixed with an acid or if exposed to

excessive heat. Because it is

corrosive, it is also potentially

harmful to the skin and eyes.1

NaHS incidents typically involve

the following three elements:

 An inadvertent spill, leak, or

mixing, whereby NaHS reacts

with an acidic solution to

produce H2S (Figure 1).

1

 Although this bulletin addresses the

hazards associated with NaHS solutions,

its precautions also apply to other

sulfide-containing substances (e.g.,

sodium sulfide), which are often used

interchangeably with NaHS, and which

also 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 inadequate

engineering controls, such as

ventilation or H2S detection

devices, coupled with

inadequate PPE.

 Inappropriate emergency

response actions by workers and

emergency responders.

This bulletin reviews selected

NaHS incidents that caused death

and injury, for example:

 Delivery drivers inadvertently

pumping NaHS into acid

storage tanks. (See Whitehall

Leather, Horween Leather, and

Prime Tanning case studies on

pages 13–15.)

Figure 1. Firefighters in

NaHS and H2S protective gear.

MIT
2

CSB Safety Bulletins offer advisory

information on good practices for

managing chemical process hazards.

Case studies provide supporting

information. Safety Bulletins differ

from CSB Investigation Reports in

that they do not comprehensively

review all the causes of an incident.

U.S. Chemical Safety and Hazard

Investigation Board

Office of Investigations and Safety

Programs

2175 K Street NW, Suite 400

Washington, DC 20037-1848

202-261-7600

www.csb.gov

 NaHS being allowed to mix with

acids in a plant sewer system.

(See Georgia-Pacific and

Westvaco case studies on pages

13-14.)

 Mixing of NaHS and an acid

inside a common spill

containment. (See Powell

Duffryn case study on page 13.)

Physical

Characteristics

and Uses of NaHS

2 CSB compiled incident data and safety

practices described throughout this

Safety Bulletin during a comprehensive

review of NaHS incidents and industry

handling practices.

3 Total U.S. production for all forms of

NaHS was approximately 269,000 tons

in 2003.

 Figure 2. Shipping

placard with UN number

and DOT hazard class.

CSB identified the following two

common management failures

during its review of catastrophic

NaHS-related incidents:2

 Failure to identify and mitigate

hazards during process system

design and engineering.

 Failure to manage hazards that

were not controlled through

good design and engineering.

Typical NaHS solutions are produced commercially by combining

H2S with caustic soda (NaOH), as

shown in the following reaction:

Table 1 summarizes the general

physical properties of NaHS

solutions.

The resulting finished solution has

a pH of approximately 11.5.

Depending on its solution strength

(22 to 60 percent NaHS), it is

heated to 71 to 82 oC to prevent

crystallization. NaHS is sold

commercially in both solution and

flake forms, with solutions

accounting for about 80 percent of

total U.S. production.3

NaHS is used in a variety of

industries (Figure 3):

 In the pulp and paper industry,

to remove lignin from wood

chips.

 In mining, as a flotation agent to

separate impurities.

 In manufacturing, as a raw

material or purifying agent.

 In the leather tanning industry,

to remove hair from hides.

H2S NaOH

NaHS + H2O

+



Molecular weight: 56.1

Specific gravity:

1.152 (a)–1.376 (b)

pH of solution:

strongly alkaline (11–12)

Solution freezing point:

-15oC(a) – 40oC(b)

Odor: rotten egg

H2S flammable limits

(% H2S in air):

Lower: 4

Upper: 44

(a) 22% solution.

(b) 60% solution.

Table 1

Physical Properties of NaHS
3

ACGIH: American Conference of Governmental

Industrial Hygienists

AIChE: American Institute of Chemical Engineers

AIHA: American Industrial Hygiene Association

ANSI: American National Standards Institute

ASSE: American Society of Safety Engineers

ATSDR: Agency for Toxic Substances and Disease

Registry, DHHS

oC: Degrees Celsius

CAS: Chemical Abstracts Service

CCPS: Center for Chemical Process Safety, AIChE

CDC: Centers for Disease Control and Prevention,

DHHS

CFR: Code of Federal Regulations

CO2: Carbon dioxide

CSB: U.S. Chemical Safety and Hazard Investigation

Board

DHHS: U.S. Department of Health and Human

Services

DOE: U.S. Department of Energy

DOT: U.S. Department of Transportation

EPA: U.S. Environmental Protection Agency

ERPG: Emergency Response Planning Guidelines, AIHA

H: Hydrogen

H2O: Water

H2S: Hydrogen sulfide

HazCom: Hazard communication, OSHA

IDLH: Immediately dangerous to life or health

MIT: Massachusetts Institute of Technology

MSDS: Material safety data sheet

Na: Sodium

NaHS: Sodium hydrosulfide

NaOH: Sodium hydroxide

NAS: National Academy of Sciences

NFPA: National Fire Protection Association

NIOSH: National Institute for Occupational Safety and

Health, DHHS

NLM: National Library of Medicine, National Institutes

of Health (NIH), DHHS

NRC: National Response Center, USCG

NTSB: National Transportation Safety Board

OSHA: Occupational Safety and Health Administration,

U.S. Department of Labor

PEL: Permissible exposure limit, OSHA

pH: Potential of hydrogen

PPE: Personal protective equipment

ppm: Parts per million

PSM: Process safety management, OSHA

PTFE: Polytetrafluorethylene

REL: Recommended exposure limit, NIOSH

SCBA: Self-contained breathing apparatus

SO2: Sulfur dioxide

STEL: Short-term exposure limit

TWA: Time-weighted average

UN: United Nations

USCG: U.S. Coast Guard

 Figure 3. NaHS use by industry section.

Copper flotation

 30%

Pulp & paper

 42%

Miscellaneous

 5%

Leather

 tanning

 10%

Chemical & dye

manufacturing

 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 marked

dryness and irritation of nose and throat. Prolonged

exposure may cause runny nose, cough, hoarseness,

headache, nausea, shortness of breath, and severe lung

damage (pulmonary edema).

200–250 Worsening and more rapid onset of the above health

effects; possible death in 4 to 8 hours.

300–500 Excitement, severe headache and dizziness, staggering,

unconsciousness, and respiratory failure likely in 5

minutes to 1 hour; possible death in 30 minutes to 4

hours.

500+ Rapid onset of severe toxicity, respiratory paralysis, and

death. If not fatal, may cause long-term effects such as

memory loss, paralysis of facial muscles, or nerve tissue

damage.

800–1,000 May be immediately fatal after one or more breaths,

resulting in an instant unconsciousness or “knock-down”

effect.

Table 2

Inhalation of H2

S

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

Health Hazard

Summary

Because NaHS is corrosive, it

presents a hazard to unprotected

skin and eyes. However, its most

serious hazard is its propensity to

produce toxic H2S gas when mixed

with an acid or exposed to high heat

sources such as a fire. The acid

reaction chemistry is shown as:

Inhalation

The gases released by NaHS are

corrosive and may contain high

levels of H2S. Inhalation of H2S is

irritating to the nose and throat.

At higher concentrations, it can

produce olfactory fatigue, a

buildup of fluid in the lungs

(pulmonary edema), severe

shortness of breath, and death.

Table 2 outlines the health effects of

inhaling H2S.

Continuous exposure to low

concentrations (5 to 10 ppm)

of H2

S or brief exposure to

higher concentrations (above

50 ppm) deadens the odordetecting nerves in the nose and

lessens the ability to smell

dangerous concentrations. The

higher the concentration of

H2S, the faster the onset of

olfactory fatigue.

H2S exposures may

cause olfactory fatigue



Eye Contact

Corrosivity hazard

Because of the high pH of NaHS

solutions (approximately 11.5),

contact may severely irritate and

burn the conjunctiva and cornea,4

and may result in permanent tissue

damage.

Hazard from generated H2S

Exposure to low concentrations of

H2S 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 disappear

when the exposure ends. Prolonged exposure to concentrations

of H2S above 50 ppm may cause

permanent damage or intense

tearing, blurring of vision, and

pain when looking at bright light.

Skin Contact

Skin contact with NaHS may

produce pain, irritation, redness

(erythema), or burns. Because

symptoms of exposure severity may

4

 The conjunctiva and cornea are the thin,

transparent tissues that cover the outer

surfaces of the eye. 

NaHS Acid (H+)

Na+ H2 + S

+


5

be delayed, affected skin should be

treated immediately. (See the first

aid guidance on page 12.)

Ingestion

Ingesting a small amount of NaHS

in a single dose will likely produce

only minor throat irritation or

burning of the esophagus.

Ingesting a larger quantity,

however—or small quantities over

an extended period—may seriously

damage the gastrointestinal tract.

In addition, NaHS that mixes with

stomach acids produces H2S and

may cause the health effects associated with inhalation (Table 2).

Incident Data

From reported data for the United

States from 1971 through 2003, CSB

identified 45 NaHS-related

incidents (Figure 4).5 Collectively,

these incidents resulted in:

 32 fatalities.

 176 injuries.

 351 medical evaluations.

 At least 10 plant or community

evacuations.

Figure 4. NaHS incidents* by industry sector.

Thirty-six of the incidents resulted

from H2S releases, and the remainder from skin or eye exposure.

The following categories of

incidents were identified during

this review:

 Improper mixing or transfer: 15

(33 percent).

 Spills: 12 (27 percent).

 Mechanical failure: 7 (16

percent).

 Improper maintenance or repair:

6 (13 percent).

Five of the 45 incidents (11 percent)

were attributed to unknown

causes.

Incident data were obtained from

OSHA, EPA, and ATSDR

databases, as well as industry

questionnaires, interviews, and

media sources. Only those

incidents that were reported and

accessible are represented.

Although the incidents reviewed

are not all-inclusive, their number

and severity clearly indicate that

NaHS presents a serious hazard in

the workplace.

Prevent Harm

Good safety management includes

identifying and evaluating hazards

during initial process planning

and design, and continues

throughout the life cycle of the

operation—both for new processes

and for modifications. This

approach allows managers and

employees to understand and

address hazards prior to startup.

Hazard control measures such as

work practice controls and PPE are

secondary layers of protection.

They should be considered only

after attempting to eliminate

hazards through design and

engineering, or when substituting

5

 The earliest recorded NaHS incident

identified during the CSB review

occurred in 1971. Regulatory reporting

requirements and industry usage

practices have changed significantly

since that time, which may account for

incident rate fluctuations among the

various industry sectors. For example,

nearly all of the leather tanning

incidents occurred between 1971 and

1990, and no transportation incidents

were reported prior to 1990. The

incidents CSB reviewed include pulping

liquor incidents in which NaHS was

used 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 a

fatality, injury, medical evaluation, or evacuation.
6

for a less hazardous material or

process is impractical.

A multidisciplinary team applying

established process safety

management principles should

identify and evaluate hazards.

These principles are outlined in the

OSHA Process Safety Management

of Highly Hazardous Chemicals

(PSM) Standard and in CCPS

publications listed at the end of

this bulletin.

The PSM Standard regulates

processes containing threshold

quantities of highly hazardous

chemicals, explosives, and

flammable liquids in amounts

exceeding 10,000 pounds. 6 NaHS

is not a PSM-covered chemical

because—despite its reactive

potential to produce large amounts

of H2S when mixed with acids or

when exposed to heat—it does not

meet the OSHA listing criteria.

CSB has recommended that OSHA

expand PSM to include chemicals

with reactive characteristics similar

to those exhibited by NaHS (i.e.,

relatively stable chemicals that

react dangerously with other

substances).7 (See the CSB Hazard

Investigation Report, Improving

Reactive Hazard Management (2002;

www.csb.gov).

Design to Eliminate

Hazards

Process systems must be designed

to prevent NaHS from inadvertently mixing with acidic solutions.

The potential for human error

during handling should be

identified and eliminated to the

maximum extent practicable.

Interviews and literature reviews

with NaHS manufacturers, trade

associations, and industry

representatives highlighted the

following design practices:

 Always treat sewers as

extensions of the process. Do

NOT add wastes without

analyzing for compatibility with

other sewer contents.

 Separate acid- and NaHScontaining waste streams, or

design the system to handle

mixing so as to prevent an

uncontrolled or otherwise

hazardous release of H2S.

 Construct separate containments

for NaHS and acid storage

containers and process

equipment.

 Install waste-stream/sewer

monitors with alarms to warn

employees of system upsets or

unfavorable acid conditions.

 Install ventilation systems and

H2S detectors and alarms at

locations where hazardous

concentrations may occur.

 Design storage tank vents to

minimize the potential for

worker exposure.

 Design transfer connections and

procedures to prevent inadvertent mixing. Limit access to

these connections to trained and

authorized personnel through

reliable and effective controls,

which should include

procedures and physical barriers

(e.g., locking devices or unique

fitting configurations).

 Construct process system

components from materials

capable of withstanding the

corrosivity and temperatures

associated with NaHS solutions.

NaHS manufacturers

recommend the following

materials:8

 Storage tanks and steam

coils: 304 stainless steel.

 Pumps: 304L or 316L

stainless steel.

 Packing: PTFE-impregnated

carbon fiber.

 Piping: 304L stainless steel,

insulated and heat-traced in

locations where freezing may

occur.

 Gaskets: Spiral-wound 316L

stainless steel or a PTFE ring.

 Plug valves: Lubricated or

made with a PTFE sleeve and

seal.

6 See 29 CFR 1910.119 at www.osha.gov/

SLTC/processsafetymanagement/.

Highly hazardous chemicals are listed in

Appendix A.

7

 Based on their reactive characteristics,

the chemicals included in Appendix A

were selected from the 1975 version of

NFPA 49, Hazardous Chemical Data.

OSHA selected only those chemicals with

instability ratings of “3” or “4” (on a

scale of 0 to 4). These ratings focus

purely on the chemicals themselves and

do not consider the consequences of

mixing with other chemicals.

8

 This information illustrates the types of

materials manufacturers recommend for

use in NaHS process systems. It is not

intended as a substitute for recognized

and generally accepted good engineering

practices for the specific facility design,

construction, or maintenance.
7

Manage Hazards

Eliminating hazards through

process design and engineering is

the optimal hazard management

system. However, additional

systems are required when design

and engineering do not eliminate

these hazards. CSB identified the

following management systems as

particularly applicable to NaHS

users.9

Communicate hazards to

employees

The OSHA HazCom Standard (29

CFR 1910.1200) is based on the

simple concept that employees

have both a need and a right to

know of the hazards associated

with chemicals to which they are

exposed. They also need to know

how to protect themselves from

adverse health effects due to

chemical exposure. The general

requirements of this standard are

outlined at www.osha.gov.

The HazCom requirements

pertaining to NaHS MSDSs and

H2S training are outlined below:

 MSDSs: Employers are required

to obtain an MSDS for each

hazardous chemical (present or

produced at the facility) and to

make them readily available to

workers. The information

contained in MSDSs may vary

significantly among NaHS

manufacturers.10 Operations and

safety personnel should,

therefore, attempt to acquire a

better understanding of NaHS

hazards through such resources

as this Safety Bulletin, MSDSs

and product information from

multiple NaHS manufacturers,

and databases such as the NLM

Hazardous Substance Data

Base.11

 Training: Employers are

required to train their employees

and inform contractors

(including delivery drivers,

construction workers, and

emergency responders) of sitespecific NaHS and H2S hazards,

including plant hazard labeling

systems and locations of

MSDSs.12 This is often

9 The safety programs outlined in this

section relate to circumstances identified

in the incidents CSB reviewed. Other

relevant safety programs—such as

management of process change, line

breaking, lockout/tagout, and process

and equipment integrity—are also

extremely important components of a

successful accident prevention program.

10 See www.csb.gov and www.osha.gov

for discussions of MSDS inconsistencies

and inaccuracies.

11 toxnet.nlm.nih.gov/index.html.

12 See Safety Requirements for H2

S Training

Criteria (ANSI Z390.1-1995, available at

webstore.ansi.org/ansidocstore/

default.asp) for a model H2S training

program.

accomplished in the form of a

facility safety orientation.

Provide personal protective

equipment

Facilities should rely on PPE only

after conducting a hazard

assessment, as required by the

OSHA Personal Protective

Equipment, General Requirements

Standard (29 CFR 1910.132).13

Employees should participate in

the selection of PPE because of the

potential for stress and discomfort

created by restrictions to movement, vision, and dexterity. Where

practical, PPE should be simple to

operate and reasonably

comfortable to wear for the

duration of the exposure.

 Chemical protective clothing:

PPE required to protect workers

from the corrosive hazards

associated with NaHS includes

eye and face protection, chemical

protective gloves, protective

clothing, and foot protection

(www.cdc.gov/niosh).

 Respiratory protection: Because

of the toxicity and potential for

olfactory fatigue associated with

H2S (see Table 3), extended

exposure above any of the OSHA

PELs14 requires use of an SCBA

or airline respirator equipped

with a full-face piece and

operated 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: separate

NaHS and acids

Allowing spilled NaHS to

inadvertently mix with an acid

(pH < 7) poses a significant risk

of harm. Similarly, if a sewer

system is not designed to control

H2S, allowing NaHS to run off to

a sewer containing acids also

poses a significant risk. Large

amounts of toxic (and flammable)

H2S may evolve very rapidly!


8

positive-pressure mode. Such

respiratory protection could be

required when transferring

materials to or from tankers,

cleaning process equipment,

responding to NaHS releases,

and performing emergency

rescue.

According to OSHA, employers

are responsible for determining

exposure for all employee

activities, including those

that expose contractors and

rugged and reliable, simpler to

operate, and much less expensive. Examples of available

devices are noted below:

 Personal H2S detectors with

audible, vibrating, and

visual alarms: These

detectors can be clipped into

a shirt pocket or worn on a

hard hat. They are relatively

inexpensive and reliable,

and have low-maintenance

electrochemical sensors and

long-lasting batteries.

 Stationary H2S detection and

notification systems: These

systems provide alarm

notification 24 hours a day

and can be used to automatically notify emergency

responders. Freestanding

solar- and battery-powered

systems are also available

that can be equipped with

radio transmitters to send

real-time monitoring results

to a remote alarm or warning

device.

Enter confined spaces safely

Because H2S is heavier than air, it

tends to concentrate near or below

ground level, especially where

there is limited air movement.

Sump pits, storage and process

tanks, valve trenches, and sewers

are particularly susceptible to high

concentrations of H2S and may

require atmospheric testing,

communications equipment, and

standby emergency rescue

personnel.

OSHA regulates confined spaces in

the Permit-Required Confined

15 A person trained in industrial hygiene

sampling practices must perform

exposure monitoring to ensure

compliance with the OSHA PEL.

16 www.osha.gov/SLTC/

respiratoryprotection/).

17 OSHA relies on NIOSH as the testing

and certifying body in 29 CFR 1910.134.

NIOSH requires end-of-service life

indicators for filters used to protect

against chemicals with poor warning

properties, such as H2S. There are

currently no approved filters for extended

protection against H2S.

OSHA (PEL)

Ceiling (a) 20 ppm

10-minute peak (b) 50 ppm

8-hour TWA 10 ppm

NIOSH

IDLH(c) 100 ppm

REL

(10-minute ceiling) (d) 10 ppm

ACGIH

15-minute STEL(e) 15 ppm

8-hour TWA 10 ppm

(a) Concentration generally not to be

exceeded during the work shift.

(b) Workers may be exposed above the

ceiling level up to this concentration

for a maximum of 10 minutes.

(c) Exposure to environments exceeding

these airborne concentrations is likely

to cause death or permanent adverse

health effects or to prevent escape.

Use of SCBA in pressure-demand or

positive-pressure mode is required

(see 29 CFR 1910.134).

(d) Exposure should not exceed the REL

for any continuous 10-minute period

during the work shift.

(e) According to ACGIH, exposure

should not exceed this level for any

continuous 15-minute period during

the work shift.

Table 3

H2

S Exposure Limits

visitors.15 If respiratory

protection is required, employers

must comply with the OSHA

Respiratory Protection Standard

(29 CFR 1910.134).16

Before relying on respirators,

facilities must have determined

that it is impractical to eliminate

or control hazards through

substitution of a less hazardous

chemical, design and

engineering controls, or work

practice or administrative

controls.

NIOSH has certified certain fullface air purifying respirators (i.e.,

a facemask equipped with a

filter) for emergency escape

purposes, but only where H2S

concentrations do not exceed 100

ppm.17 For all other situations,

NIOSH prescribes supplied-air

respirators. These requirements

are outlined in the NIOSH Pocket

Guide to Chemical Hazards (2003;

www.cdc.gov/niosh/npg/

npg.html).

 Air monitoring for H2S: In

environments that are normally

safe, but which pose the risk of

hazardous H2S exposure, the

only way to ensure worker safety

is to continuously monitor the

air. In recent years, H2S monitors

have become much smaller, more
9

Spaces Standard (29 CFR

1910.146).18 Further information

and guidance on this standard is

provided in the references section

of this bulletin.

Handle and store NaHS safely

The hazards associated with NaHS

require employers to establish

facility-specific safe handling and

storage practices and procedures

for both employees and contractors.

These practices and procedures

include:

 Controlling access and

supervising product delivery

and transfer.

 Installing local exhaust

ventilation on process or storage

equipment where personnel

exposure is likely and ensuring

that such systems are operating

properly before starting a

process.

 Installing fixed H2S monitors

with alarms in NaHS storage

and offloading areas where

concentrations could exceed safe

levels.

 Providing PPE and emergency

eyewash and shower facilities

where there is a risk of exposure

to NaHS.

 Ensuring that NaHS-containing

wastes are not flushed to acidcontaining sewers without

controls to prevent a release of

H2S.

 Storing NaHS separately from

low pH (acidic) materials to

avoid inadvertent mixing.

 Decide whether to evacuate or

shelter-in-place: This decision

is made under urgent conditions.

Factors that must be considered

include population distribution,

risk of exposure, adequacy of

available shelters, evacuation

time requirements, and other

factors such as the characteristics of the chemical released

and weather conditions. This

issue has been studied

thoroughly by researchers at the

Oak Ridge National Laboratory,

as documented in Planning

Protective Action Decision-Making:

Evacuate or Shelter-in-Place?

(USDOE, 2002; www.osti.gov/

bridge/).

A decision to evacuate should be

based on the reasonable

assurance that movement is in

the best interest of those being

evacuated:

 Evacuation: Downwind of a

release—before starting to

move upwind—unprotected

personnel should move

directly crosswind to onehalf of the downwind

distance from the spill. The

crosswind distance varies in

relation to the size of the spill

and downwind distance.

See Figure 5 and Table 4 for

the initial isolation and

protective action distances

recommended by the DOT

Emergency Response

Guidebook (2000;

hazmat.dot.gov/

gydebook.htm).

 Clearly labeling NaHS containers, process piping, and

critical process piping valves

that may contain NaHS with

essential hazard information.

 Warning against exposure of

NaHS to excessive heat or

storage near open flames or other

ignition sources that might

generate or ignite flammable H2S.

 Ensuring that storage containers

and process equipment materials

are compatible with the

alkalinity of NaHS. Manufacturers of NaHS warn against

using copper, zinc, or aluminum.

 Implementing an emergency

notification system to inform

emergency responders and

potentially impacted offsite

residents of threatening

incidents.

Emergency

Response

Emergency responders must

immediately take precautions in

the case of a fire or spill involving

NaHS. If there is evidence of an

H2S release—either the presence of

its characteristic rotten egg odor or

affirmative H2S monitoring

results—emergency responders

should:

 Restrict access to the spill/

release site: Allow only

emergency personnel equipped

with proper PPE to enter the area

(i.e., NIOSH-approved, full facepiece SCBA in pressure demand

mode, and protective outer

garments).

18 www.osha.gov/SLTC/

confinedspaces/
10

 Shelter-in-place: This is a

precaution to keep people

safe while remaining

indoors. It calls for taking

refuge in a preferably small,

interior room with no or few

windows; closing windows

and doors; turning off

heating and air-conditioning

systems; and listening to

local TV/radio for emergency response directions.

Offsite residents or plant

personnel who may be

required to shelter-in-place

must be provided with

instructions and training,

and must have necessary

supplies 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 more

protective than AIHA ERPGs. Interim

exposure levels for H2S are available at

www.epa.gov/oppt/aegl/.

Figure 5. Initial isolation and evacuation diagram.

information regarding

shelter-in-place is available

at www.cdc.gov/ and

www.redcross.org/.

 Conduct continuous downwind

monitoring: Determine if H2S

concentrations exceed the AIHA

ERPGs19 (ERPG–3 or –2 values

from Table 5) or the OSHA PEL;

and continue to evacuate or

shelter-in-place as required.

Firefighting

Contact between NaHS and an

acid—or exposure to excessive

heat—liberates H2S, which

presents an inhalation and fire

Small Spill (a)

1. Isolate spill area 100 feet in

all 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 in

all 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 or

smaller) or a small leak from a large

package.

(b) Sunrise to sunset.

(c) From a large package or from many

small packages.

Source: USDOT, 2000.

Table 4

H2

S Initial Isolation

and Protective Action

Distances

Downwind distance from spill

Wind direction

Spill/release

Initial isolation

zone 1/2

Downwind

distance

1/2

Downwind

distance
11

hazard. In addition, burning H2S

produces sulfur dioxide (SO2),

which is a severe respiratory

irritant that can be life threatening.

If a fire involves NaHS, the DOT

Emergency 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, or

water spray.

 Move containers of NaHS

from fire area if possible to

do so without risk.

 Contain contaminated fire

control water for later

disposal.

 Fires involving a tank, railcar, or

tank truck:

 Fight the fire from the

maximum distance possible,

or use unmanned hose

holders or monitor nozzles.

 Do NOT allow water to enter

containers of NaHS.

 Cool containers with

flooding amounts of water

until well after the fire is

extinguished.

 Withdraw immediately in

case of a rising sound from

venting safety devices or

discoloration of the tank.

 ALWAYS stay away from

burning tanks.

Spill Response

In the event of a NaHS spill:

 Do NOT allow NaHS to come in

contact with acids.

 Contain the spill. Do NOT flush

to a sewer unless the sewer is

designed and engineered to control the H2S that may be released.

 Remove sources of ignition so

that any H2S released will not

ignite.

 Provide maximum ventilation.

 Recover spilled material on

adsorbents, such as sand or

vermiculite, and place in covered

containers for reclamation or

disposal.

 For spills that exceed the 5,000-

pound reporting threshold,22

22 NaHS is listed in Table 302.4 of the

Superfund, Emergency Planning and

Community Right-to-Know Act (40 CFR

302) as a hazardous substance with a

reportable quantity of 5,000 pounds,

based on 100 percent purity (approximately 1,077 gallons of 43 percent

solution). See www.epa.gov/swercepp/

factsheets/epcra.pdf for more

information.

20 See Guide 154 for NaHS.

21 Some manufacturers and fire safety

professionals caution against using

extinguishers containing CO2 and dry

chemical extinguishing media because

they form acids when mixed with water

and may exacerbate the generation of H2S

when used on fires involving NaHS.

They recommend using water in flooding

quantities to fight the actual fire, and

water spray or foam to control vapors.

If CO2 or dry chemical extinguishers are

used, responders must wear proper

respiratory protection (i.e., SCBA).

60-Minute

Concentration

(ppm)

ERPG–3 (a) 100

ERPG–2 (b) 30

ERPG–1 (c) 0.1

(a) ERPG–3 is the maximum airborne

concentration below which it is

believed that nearly all individuals could

be exposed for up to 1 hour without

experiencing or developing lifethreatening health effects.

(b) ERPG–2 is the maximum airborne

concentration below which it is

believed that nearly all individuals could

be exposed for up to 1 hour without

experiencing or developing irreversible

or other serious health effects or

symptoms that could impair their

ability to take protective action.

(c) ERPG–1 is the maximum airborne

concentration below which it is

believed that nearly all individuals could

be exposed for up to 1 hour without

experiencing other than mild transient

adverse health effects or perceiving a

clearly defined objectionable odor.

Source: AIHA, 1991.

Table 5

H2S Emergency Response

Planning Guidelines
12

notify NRC at 1-800-424-8802 or

www.nrc.uscg.mil.23

Emergency Responders

Emergency responders must wear

NIOSH-approved, full face-piece

SCBA in pressure-demand or

positive-pressure mode and

chemical-resistant outer garments

when there is a threat of airborne

concentrations of H2S exceeding

the PEL. To avoid endangering

emergency responders, NaHS- or

H2S-contaminated outerwear

should be discarded and victims

decon-taminated prior to placing

them in a confined space, such as a

medical transport vehicle.

First Aid

Each year a large number of

fatalities result from failed rescue

attempts by those who rush into

dangerous environments to help

fallen workers. First responders and

emergency medical personnel must

protect themselves before rendering aid

to others.

24 Eight contractor employees were

injured during the Georgia-Pacific

incident when they remained in the zone

of danger to assist with the rescue of

fallen workers.

25 In some states, administering oxygen

requires emergency medical certification.

Chemical shower and eyewash

facilities must meet the requirements outlined in the OSHA

Medical Services and First Aid

Standard (29 CFR 1910.151(c)).26

Applying elements of the

Emergency Eyewash and Shower

Equipment standard, ANSI Z358.1-

2004, fulfills OSHA requirements

and provides adequate protection

to workers.27

Skin Contact

Immediately remove contaminated

clothes and irrigate exposed skin

with copious amounts of water for

at least 15 minutes, regardless of

symptoms. A physician may need

to examine the exposed area if

irritation or pain persists or

worsens.

Ingestion

Do NOT induce vomiting or

attempt to neutralize ingested

NaHS. Immediately request

emergency medical assistance by

calling 911 and the national Poison

Control Center emergency hotline

at 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 for

purchase at webstore.ansi.org/

ansidocstore/default.asp.

Emergency rescue

If H2S is present, do NOT

attempt to rescue a fallen worker

without proper PPE.



Emergency responders responsible

for facilities that handle NaHS

should familiarize themselves with

the ATSDR Medical Management

Guidelines for H2S (2003;

www.atsdr.cdc.gov/MHMI/

mmg114.html). Do NOT enter an

unknown or potentially hazardous

environ-ment without ensuring

that it is safe by sampling the air

and/or wearing proper PPE.

24

Inhalation of H2S

Move the victim into fresh air and

administer oxygen as necessary.25

Victims of overexposure to H2S (or

NaHS vapors that may contain

H2S) should immediately receive

emergency medical attention.

Eye Contact

In the event of eye contact with

either NaHS or high concentrations of H2S, immediately

irrigate the eyes with copious

amounts of water for at least 20

minutes, or until the arrival of

emergency medical personnel. An

ophthalmologic examination

should be conducted as soon as

possible because the extent of some

injuries related to corrosive eye

exposure may not be apparent for

48 to 72 hours.

23 This is a regulatory threshold reporting

quantity established by EPA with an

emphasis on identifying adverse environmental impact. Spills and releases of

much smaller quantities of NaHS can

lead to catastrophic consequences. For

example, the spillage of about 100

gallons of NaHS led to the GeorgiaPacific incident, reviewed on page 13.
13

Whitehall Leather Company,

Whitehall, Michigan

(1 killed, 1 injured)

On June 4,

1999, the

driver of a

tanker truck

filled with

NaHS

inadvertently

pumped the

tanker contents

into a storage

tank partially

filled with

“pickle acid”

(hydrochloric

acid). The

tanker truck

had arrived at

the plant

during the

night shift.

The shift supervisor—never having

received a shipment of NaHS and

believing it to be pickle acid—

directed the driver to unload it into

a pickle acid storage tank (Figure

6). The resulting reaction released

H2S, which killed the driver and

injured a plant employee.

Powell Duffryn terminal fire,

Savannah, Georgia

(337 medical evaluations,

community evacuation)

On April 10, 1995, the force from an

explosion in a solvent storage tank

fractured NaHS transfer piping.

Up to 300,000 gallons of NaHS

spilled and mixed with a similarly

large quantity of acidic cleaning

solution (Figure 7). The NaHS and 28 CSB investigators estimated that 100

gallons of NaHS was allowed to

accumulate in the pit.

Selected Case

Studies

Georgia-Pacific, Naheola pulp

and paper mill, Pennington,

Alabama (2 killed, 8 injured)

On January 16, 2002, two workers

were killed and eight injured while

performing maintenance near a

NaHS transfer terminal. NaHS

had recently been pumped from 15

tanker trucks into storage tanks.

Because of a leaking pump, NaHS

accumulated in a containment pit

that was connected to the plant

acid sewer.

When the containment pit was

drained, a relatively small quantity

of NaHS28 reacted with acid in the

sewer to produce H2S. The H2S

leaked through a faulty manway

cover seal into the area where the

contractors were working.

The CSB investigation concluded

that Georgia-Pacific management

was unaware that the containment

pit drained to the acid sewer.

However, neither Georgia-Pacific

nor the previous plant owners had

adequately evaluated the potential

for hazardous chemical mixing in

the sewer system and the release of

deadly amounts of H2S.

Consequently, plant personnel,

contract workers, and emergency

responders were unaware of and

unprepared for the dangers.

 Figure 6. Whitehall Leather offloading area.

NTSB

acid solution tanks were colocated

inside an earthen containment.

The reaction released an enormous

volume of H2S, which caused 337

people to seek medical evaluations

and forced 2,000 downwind

residents to evacuate. The

evacuation lasted more than 30

days as H2S continued to evolve

from NaHS-saturated soil.

This incident illustrates the failure

of management systems to identify

and evaluate the hazards associated with colocating

incompatible materials inside a

single spill containment. The EPA

investigation report (1998) is

available at yosemite.epa.gov/

opa/admpress.nsf/0/

8e314f057b62e118852565fe006fa986?

OpenDocument.
14

Stone Savannah River pulp and

paper mill, Wentworth,

Georgia (1 killed, 4 injured)

On December 8, 1990, one worker

was killed and four injured when a

large quantity of H2S formed

during acid cleaning of a 20,000-

gallon pulping solution pressure

filter. H2S was routinely produced

inside the process vessel when the

cleaning solution was used to

dissolve NaHS-containing pulping

filtrate. Local exhaust ventilation

normally controlled the H2S.

 However, on the day of this

incident, H2S leaked from the

system and accumulated inside the

walled containment where workers

were operating valves. According

to witnesses, the workers immediately smelled H2S and tried to

escape, but were overwhelmed

before being able to climb out of the

valve pit. This incident highlights

Figure 7. Powell Duffryn fire.

the dense gas properties of H2S and

the atmospheric hazards that may

be present in confined spaces.

WESTVACO paper mill,

Covington, Virginia

(10 injured)

On May 4, 1988, 10 employees were

hospitalized for H2S exposure

when a 300,000-gallon storage tank

containing pulping solution

Figure 8. WESTVACO paper mill tank failure.

collapsed (Figure 8). The plant

sewer system routinely controlled

storm runoff, spills, and

discharged wastes.

However, when the NaHScontaining pulping solution

entered the sewer, it reacted with

waste acids and produced H2S—

which escaped via drains, vents,

and manways. The 10 injured

employees were working at various

locations near the vents and

manways.

Horween Leather Company,

Chicago, Illinois

(8 killed, 43 injured)

On February 14, 1978, eight

workers were killed, 43 were

injured, and 57 sought medical

evaluation after being overwhelmed by H2S. The incident

began when a substitute delivery

driver unloaded a tanker truck of

NaHS into a storage tank

containing an acid. He was

unfamiliar with plant operations

and NaHS hazards, and was

unsupervised by plant personnel.

EPA

Crawford Akers Photography
15

 A large volume of H2S was

immediately generated, which led

to evacuation of the entire plant

and surrounding community.

Although the tank fill line coupling

was designed to prevent inadvertent mixing, the driver created a

makeshift coupling when he was

unable to attach the line from the

truck.

Prime Tanning Company,

Berwick, Maine (6 killed)

On April 2, 1971, six workers died

when NaHS was inadvertently

pumped into a tank containing

acidic chrome tanning liquor,

which has a pH of 3 to 4. The

NaHS delivery drivers had been

instructed where to offload their

tanker truck.

When the drivers discovered that

the truck’s fill nozzle would not fit

the tank’s coupler, they used an

adapter nozzle. There was no

labeling on the tank to identify its

contents or to warn of the potential

hazard. Approximately 160

gallons of NaHS had been

transferred to the tank before one of

the drivers noticed that workers

inside the plant were collapsing.

NaHS had mixed with the chrome

liquor to produce H2S.

References and

Additional

Information

ANSI/ASSE, 2003. Safety

Requirements for Confined Spaces,

Z117.1–2003 (webstore.ansi.org/

ansidocstore/default.asp).

ANSI/ASSE, 1998. Emergency

Eyewash and Shower Equipment,

Z358.1-1998.

ANSI/ASSE, 1995. Safety

Requirements for H2S Training

Criteria, Z390.1-1995.

ATSDR, 2003. Medical Management

Guidelines for Hydrogen Sulfide

Gas, August 2003

(www.atsdr.cdc.gov/MHMI/

mmg114.html).

ATSDR, 1999. Toxicological Profile

for Hydrogen Sulfide.

Bretherick, Leslie, P. G. Urben, and

Martin J. Pitt, 1999. Bretherick’s

Handbook of Reactive Chemical

Hazards, Sixth Edition, Vol. 1,

Butterworth-Heinemann.

CCPS, 2003. Essential Practices for

Managing Chemical Reactive

Hazards, AIChE

(www.aiche.org).

CCPS, 1996. Inherently Safer

Chemical Processes, A Life Cycle

Approach, AIChE.

CCPS, 1994. Guidelines for

Preventing Human Error in Process

Safety, AIChE.

CCPS, 1992. Guidelines for Hazard

Evaluation Procedures, AIChE.

CCPS, 1989. Guidelines for Technical

Management of Chemical Process

Safety, AIChE.

Health and Safety Executive (HSE),

2000. Designing and Operating

Safe Chemical Reaction Processes,

Norwich, U.K.: HSE Books.

McManus, Neil, 1999. Safety and

Health in Confined Spaces, Lewis

Publishers/CRC Press.

NFPA, 1975. Hazardous Chemical

Data, NFPA 49.

NIOSH, 2003. Recommendations for

Chemical Protective Clothing, A

Companion to the NIOSH Pocket

Guide to Chemical Hazards, Table

H, August 2003 (www.cdc.gov/

niosh/npg/npg.html).

NLM Hazardous Substance Data

Base (toxnet.nlm.nih.gov/

index.html).

OSHA, 1993. Selected occupational

fatalities related to pulp, paper

and paperboard mills as found in

OSHA fatality/catastrophe

investigations, June 1993

(www.osha.gov).

Rekus, John F., 1994. Complete

Confined Spaces Handbook, Lewis

Publishers/CRC Press.

Sayers, Robert H., 1979. “Safety in

Handling and Using Sulfide,

Sulfhydrate, and Other

Hazardous Chemicals in a

Tannery,” Journal of American

Leather Chemists Association,

Vol. 74, pp. 64–69.
16

Shih, Thomas, et al., 1967.

“Hydrogen Sulfide Vapor—

Liquid Equilibrium in Aqueous

Systems as a Function of

Temperature and pH,” TAPPI

Journal, Vol. 50, No. 12, pp. 630–

634, December 1967.

The Innovation Group, 2003.

Chemical Profiles (www.theinnovation-group.com).

USCG, 2001. Chemical Hazards

Response 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 Hazard

Management, Report No. 2001-01-

H, December 2002

USDOE/Oak Ridge National

Laboratory, 2002. Planning

Protective Action Decision-Making:

Evacuate or Shelter-in-Place?

ORNL/TM-2002-144, prepared

for Federal Emergency

Management Agency

(www.otsi.gov/bridge/).

USDOT, 2000. North American

Emergency Response Guidebook,

J. J. Keller and Associates

(hazmat.dot.gov/gydebook.htm).

USEPA, 1998. EPA Chemical

Accident Investigation Report,

Powell Duffryn Terminals, Inc.,

Savannah, Georgia, Office of Solid

Waste 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 is

to 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 Clean

Air 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 government

agencies involved in chemical safety.

No part of the conclusions, findings, or recommendations of CSB relating to any chemical incident may be admitted

as 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, summary

reports, safety bulletins, safety recommendations, case studies, incident digests, special technical publications, and

statistical reviews. More information about CSB may be found at www.csb.gov.

CSB investigation reports may be purchased from:

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161-0001

(800) 553-NTIS or (703) 487-4600

Email: info@ntis.fedworld.gov

For international orders, see:

www.ntis.gov/support/cooperat.htm.

CSB publications may be downloaded at www.csb.gov or

obtained by contacting:

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Office of Government, Public, and Board Affairs

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(202) 261-7600