H2S is a colorless, flammable, and 

corrosive gas with an odor similar to 

rotten eggs. People can lose their ability 

to smell H2S, even at low concentrations, 

a condition called olfactory fatigue. 

Because of olfactory fatigue, OSHA 

warns that the sense of smell should 

not be used as a detection method. 

According to the National Institute for 

Occupational Safety and Health (NIOSH), 

H2S environmental concentrations of 100 

ppm are immediately dangerous to life 

or health, concentrations greater than 

500 ppm can cause a person to collapse 

within five minutes, and concentrations 

exceeding 700 ppm can cause immediate 

collapse, and death, within just one or 

two breaths. The OSHA permissible 

exposure limit (PEL) for H2S is 20 ppm 

(29 CFR 1910.1000 Table Z-2) and is not to 

be exceeded at any time during an 8-hour 

shift, except if the exposure is 50 ppm 

for no more than 10 minutes in an 8-hour 

shift so long as no other measurable 

exposure occurs.

BRIEF DESCRIPTION OF INCIDENT*

A worker died of acute hydrogen sulfide (H2S) poisoning while 

responding to an alarming water pump involved in the process of 

extracting crude oil and natural gas. The worker was alone in the pump 

house attempting to close process valves to isolate the pump. Either 

before the worker’s arrival or during his work, the pump unexpectedly 

energized, releasing water containing H2S gas into the pump house. 

H2S monitors in and around the building were not functioning, and 

the worker was not wearing a personal H2S gas detector. The H2S 

concentration reached fatal levels killing the worker. A few hours later, 

out of concern that she had not heard from her husband in a while, 

the worker’s spouse entered the facility and died from H2S poisoning. 

Emergency responders noted they could smell H2S as soon as they 

entered the facility. As they approached the pump house, the smell 

of H2S was overwhelming even though the pump houses’ bay doors 

were partially open and there were no H2S alarms.

LIKELY CAUSES

The employer knew about the potential H2S exposure hazard, but did 

not establish and enforce a formal policy requiring employees to wear 

personal H2S detectors while in the pump house or adhere to OSHA’s 

standard on air contaminants, 29 CFR 1910.1000. 

Although the facility had been equipped with multiple H2S detection 

and alarm systems, none of the detectors communicated with the 

system’s control panel. Some detectors had been set to a testing 

mode, preventing any alarm signals from being sent by any of those 

detectors to the alarm control panel. Other detectors that were 

correctly set up were also unable to send a signal to the control room. 

The employer supplied personal H2S gas detectors, which would have 

notified the worker of the potential exposure with an audible alarm, 

but they did not have formal written policies requiring their use.

The following contributed to the deaths. The employer:

• Failed to maintain and properly configure the H2S detection and 

alarm system. 

• Failed to enforce operator use of personal H2S detectors when in the 

vicinity of equipment or facilities with the potential for an H2S release.

• Failed to develop, train, and enforce lockout/tagout procedures.

• Failed to evaluate the ventilation systems of the building to ensure it 

was adequately ventilated and in working condition. 

• Lacked a robust safety management program.

• Did not establish procedures prohibiting untrained visitors from 

entering processing buildings; which allowed the employee’s spouse to 

access the facility and her subsequent toxic H2S exposure and death.

* Some of the information in this FatalFacts was obtained from the US Chemical Safety and Hazard Investigation Board Final Investigation Report on Aghorn Operating 

Waterflood Station Hydrogen Sulfide Release: www.csb.gov/file.aspx?DocumentId=6155.

FATALFacts 18No. 18 – 2023

Hydrogen Sulfide Release

U.S. Department of Labor Occupational Safety and Health Administration www.osha.gov • (800) 321-OSHA (6742)

Photo: U.S. Chemical Safety and Hazard Investigation Board
INCIDENT PREVENTION

H2S hazards during oil and gas production activities are generally well 

known. In this instance, H2S is a known hazard for oil and gas activities 

in the Permian Basin where this facility was located. Employers must 

implement appropriate safeguards against H2S exposure hazards.

Employers must have engineering and administrative controls 

for air contaminants whenever feasible in compliance with 29 

CFR 1910.1000(e). When such controls are not feasible to achieve 

full compliance, protective equipment or any other protective 

measures must be used to keep the exposure of employees to air 

contaminants within the limits of OSHA’s air contaminants standard, 

29 CFR 1910.1000. Respirators must comply with NIOSH guidelines 

for respiratory protection and OSHA’s standard on respiratory 

protection, 29 CFR 1910.134. Whenever respirators are used, employers 

shall ensure that the selected respirators are certified and used in 

compliance with their certification conditions in accordance with 

29 CFR 1910.134(d)(1)(ii). The NIOSH division of National Personal 

Protective Technology Laboratory (NPPTL) provides a certified 

equipment list that is regularly updated as respirators are approved, 

made obsolete, or the status changes in any way. 

Additionally, if the pump had been properly isolated under a lockout/

tagout program, it is less likely the worker would have been exposed 

to such high concentrations of H2S. Employers must have a formalized 

lockout/tagout program to isolate equipment from energy sources. 

This program should emphasize energy control procedures, training, 

and periodic inspections in compliance with OSHA’s control of 

hazardous energy standard 29 CFR 1910.147.

The US Chemical Safety and Hazard Investigation Board (CSB), an 

independent federal agency charged with investigating industrial 

chemical accidents, recommend the following to the employer: 

• Mandate the use of personal H2S detection devices as an integral part 

of every employee or visitor personal protective equipment (PPE) 

kit prior to entering the vicinity of the facility. Ensure detector use 

is in accordance with manufacturer specifications. (2020-01-I-TX-1, 

abbreviated)

• Commission an independent and comprehensive analysis of each 

facility ventilation design and mitigation systems to ensure that 

workers are protected from exposure to toxic gas (2020-01-I-TX-3, 

abbreviated)

• Ensure the H2S detection and alarm systems are properly maintained 

and configured and develop site-specific detection and alarm 

programs and associated procedures based on manufacturer 

specifications, current codes, standards, and industry good practice 

guidance (2020-01-I-TX-5, abbreviated).

Employers in the oil and gas production industries should develop 

and implement a written formal site-specific security program to 

prevent unknown and unplanned entrance of non-employees to the 

facility. Site security for petroleum and petrochemical facilities should 

follow industry standards and guidance such as ANSI/API Standard 

780, Security Risk Assessment Methodology for the Petroleum and 

Petrochemical Industries, and API RP 781, Facility Security Plan 

Methodology for the Oil and Natural Gas Industries. 

YOU HAVE A VOICE 

IN THE WORKPLACE

The Occupational Safety and Health 

Act of 1970 (OSH Act) affords workers 

the right to a safe workplace and the 

right to speak up about hazards without 

fear of retaliation (see OSHA’s Worker 

Rights page, www.osha.gov/workers). 

Workers also have the right to file a safety 

& health complaint with OSHA if they 

believe that there are either violations of 

OSHA standards or serious workplace 

hazards. In addition, if workers are 

retaliated against for exercising their 

rights under the OSH Act, they may file 

a whistleblower complaint with OSHA 

within 30 days of the alleged retaliation.

HOW OSHA CAN HELP

For questions or to get information or 

advice, to report an emergency, fatality, 

hospitalization, amputation, or loss of an 

eye, or to file a confidential complaint, 

contact your nearest OSHA office, visit 

http://www.osha.gov or call our toll-free 

number at 1-800-321-OSHA (6742), TTY 

1-877-889-5627. It’s confidential

MORE INFORMATION

• OSHA standards and regulations: www.

osha.gov/law-regs

• OSHA publications: www.osha.gov/

publications

• OSHA-approved state plans: www.

osha.gov/stateplans

• OSHA’s free On-site Consultation 

services: www.osha.gov/consultation

• Training resources: www.osha.gov/

training

• Help for Employers: www.osha.gov/

employers
DSG FF-4204 01/2023

Note: The described case was selected to increase awareness of the risk discussed and prevent similar fatalities. The incident prevention 

recommendations do not necessarily reflect the outcome of any legal aspects of this case. OSHA encourages your company or organization 

to duplicate and share this information.

This Fatal Facts is not an OSHA standard or regulation and it creates no new legal obligations. The recommendations contained herein are advisory 

in nature and are intended to assist employers in providing safe and healthful workplaces. The Occupational Safety and Health Act of 1970 (OSH Act) 

requires employers to comply with safety and health standards promulgated by OSHA or by an OSHA-approved state plan. The requirements of OSHA 

approved state plans can be reviewed by selecting the state’s website at: www.osha.gov/stateplans. The OSH Act’s General Duty Clause, Section 5(a)

(1), requires employers to provide employees with a workplace free from recognized hazards likely to cause death or serious physical harm.

For assistance, contact us. We can help. It’s confidential.

ADDITIONAL RESOURCES

The following CSB report provides a detailed incident report: Aghorn Investigation Report

The following resources provide additional information on chemical hazards, respiratory protection, H2S, and the 

control of hazardous energy:

• OSHA Chemical Hazards and Toxic Substances Safety 

and Health Topics

• OSHA Respiratory Protection Safety and Health Topics

• OSHA Lockout/Tagout Safety & Health Topics, Fact Sheet, 

Guidance Booklet, eTool

• For the oil and gas extraction industry specifically:

– OSHA Safety & Health Topics and eTool

– Harwood Grant Training Materials PowerPoint

– LOTO OSHA Harwood Grant Training Materials 

PowerPoint

• OSHA Hydrogen Sulfide Safety & Health Topics, Fact 

Sheet, eTool, and Quick Card

• NIOSH H2S Safety and Health Topics

• NIOSH National Personal Protective Technology 

Laboratory (NPPTL)

• Oil & Gas Well Drilling Common Incidents Asphyxiation

• OSHA-NIOSH Hazard Alert: Health and Safety Risks for 

Workers Involved in Manual Tank Gauging and Sampling at 

Oil and Gas Extraction Sites