Home / Dust & Air / Hydrogen Sulfide in Manure Pits

Hydrogen Sulfide in Manure Pits

Hydrogen sulfide can be released when manure is stirred, and it can be deadly. Danger: this is among the most serious hazards on livestock farms.

What is hydrogen sulfide?

Hydrogen sulfide is a toxic gas that can be produced as manure breaks down without oxygen. It can build up in pits, tanks, and storages, and it can be released suddenly when manure is agitated, pumped or disturbed.

It is often described as smelling like rotten eggs at low levels, but smell is not a reliable warning. At higher levels it can dull the sense of smell, so a person may stop noticing it while the danger rises.

Exposure limits and symptoms at different levels come from official sources such as NIOSH and OSHA, so this guide does not list numbers. Read them at the source.

Why is it so dangerous?

Hydrogen sulfide can overcome a person quickly, causing collapse. Some people who go to help a collapsed worker have also been overcome, which is why safety organizations stress that rescuers must not enter without proper equipment and training.

Pits and enclosed manure storage can also lack oxygen or contain other harmful gases, so the hazard is not only one gas. A filter respirator does not solve these problems.

Treat every manure pit, tank or enclosed storage as a place where air can be unsafe at any time.

When is the risk highest?

Risk tends to rise when manure is agitated, pumped out or moved, because gas trapped in the liquid is released. Work in or near buildings with pits under the floor, in poorly ventilated spaces, or during pumping can be especially hazardous.

Official extension materials describe how timing, ventilation, animals and people management come together during pumping. Read them before the job, and follow the procedures they describe.

Have a plan for moving people and animals and for ventilating buildings before any agitation begins.

What does prevention look like in principle?

Prevention starts with avoiding entry. Design and manage systems so that no one needs to enter pits or tanks, and use equipment that can be operated from outside. Keep covers, grates and warning signs in good repair and keep children away.

Plan agitation and pumping with experts, use strong ventilation, and keep people out of buildings as advised by official guidance. Some custom manure haulers are trained in these hazards, and your extension office can help you find one.

Confined space rules apply to many manure storages. Learn about entry procedures, atmosphere testing and rescue planning from OSHA, NIOSH and recognized hands-on training.

• Avoid entering pits and tanks
• Maintain covers, grates and signs
• Plan pumping and agitation with trained help
• Ventilate buildings and move people and animals as advised
• Train everyone on the hazard and the emergency plan

Can a respirator or mask protect you?

Not a simple one. Filtering respirators do not supply oxygen and are not appropriate for unknown or toxic atmospheres. Special equipment exists for trained teams, but it requires medical evaluation, fit testing, and procedures.

Do not improvise protection. If entry is truly necessary, it must follow formal confined space procedures with testing and standby rescue.

Check official sources for the equipment and training that apply.

What should you do if someone collapses?

Call 911 immediately. Tell the dispatcher that a person may have collapsed in or near a manure pit and that toxic gas may be present. Keep everyone else out of the area.

Do not enter to attempt a rescue unless you are trained and equipped. Wait for responders and meet them to give information about the location and conditions.

Anyone who was exposed should be checked by medical professionals even if they seem to recover.

Where can you get training?

Extension safety programs, agricultural safety organizations, fire departments and OSHA outreach can provide training or point you to it. Some local fire and rescue departments offer farm rescue programs, and introducing them to your farm in advance helps in an emergency.

Share the plan with every worker and family member who is old enough to understand it.

Think about visitors and neighbors too. Custom haulers, repair crews and family members may arrive without knowing which buildings have pits. Tell them about the hazard before they start and show them where the warning signs and exits are.

Last reviewed: November 12, 2026. Written by the Farm Safety Editorial Team. See our editorial policy.