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Silo Gas Dangers

Fresh silage can release gases that are dangerous to breathe, sometimes within hours of filling. This article describes the hazard in general terms and points you to official sources for details.

Why do silos produce gas?

When chopped forage is packed into a silo, natural fermentation begins. Along the way, gases can be released into the structure and the spaces around it. Some of these gases can irritate the lungs, and some can displace the air you need to breathe.

Extension services describe the process and the timing in detail for different structures and crops. Ask them about the guidance for your type of silo instead of relying on rules of thumb.

The timing and duration of gas production vary with the crop, moisture and structure, which is why published extension guidance is better than local rules of thumb.

Why are silo gases so dangerous?

Some gases can cause injury even at levels that are hard to notice. Others are heavier than air and can settle in low spots, rooms and chutes connected to the silo. A person who breathes harmful air can become confused or collapse without warning.

Because the hazard may not be visible or have an obvious smell, you cannot judge safety with your senses. This is why official guidance emphasizes staying out and getting trained advice.

Some gases are colored or noticeable, others are not. Never assume that a lack of smell or color means a lack of danger.

• Gases can collect in low areas
• Effects can come on quickly
• Senses are not a reliable warning

Where can gas travel on the farm?

Gas can move from the silo into feed rooms, barns and adjacent structures through chutes, doors and other openings. A space that has nothing to do with the silo's opening can still be affected.

Think about how air moves in your layout. Ask a qualified safety educator to help you map where gas could travel and what to do about it, such as keeping people and animals away from certain areas for a period.

Keep doors and openings between the silo and animal housing managed according to official guidance, and warn everyone who works nearby.

• Feed rooms and chutes connected to the silo
• Barns and milk rooms sharing air with the silo
• Low spots and pits near the base
• Stairwells and basements

What are the symptoms people should take seriously?

Coughing, burning eyes or throat, difficulty breathing, headache, dizziness or unusual tiredness after being near a silo should be taken seriously. Symptoms can sometimes appear hours after exposure.

If someone has any of these symptoms, get them to fresh air if it is safe to do so and call 911 or seek medical care. Tell the medical team about the silo exposure.

Chronic or repeated exposure may also affect health. Tell your doctor that you work around silos so that they can watch for lung problems.

• Cough, burning eyes or a sore throat
• Shortness of breath or chest tightness
• Headache, dizziness or unusual fatigue
• Symptoms that start later in the day or the next day

What does prevention look like in principle?

Prevention starts with not entering a silo or the spaces near it during the period when gases are likely, and with keeping children and animals away. It also includes ventilating spaces according to official advice, and using trained people and proper testing equipment when entry is unavoidable.

Exact time periods, ventilation steps and exposure limits come from official sources and not from this page. Check with your extension office, OSHA and NIOSH.

Ask whether gas monitoring equipment is appropriate for your operation, and only use it with proper training.

• Keep people and animals away during the risky period
• Follow official guidance for ventilation
• Use trained people and proper testing for any entry

Do animals and children need special attention?

Animals in barns attached to silos can be affected by gas that drifts in. Children may not understand why silo areas are off limits and can be drawn to ladders or chutes.

Keep silo areas closed and signed. Talk with children and with visiting relatives about where they are not allowed to go, and why.

Post warning signs at silo entrances and on feed room doors, and keep them visible and in good condition.

Where can you learn more?

NIOSH, OSHA and university extension programs, including Penn State Extension, publish public information about dangerous gases on farms. Local agricultural safety programs may also offer demonstrations.

If you suspect someone has collapsed in or near a silo, call 911 immediately. Do not enter to help, because rescuers can be overcome by the same gas.

Memorial stories from farm communities often include a would-be rescuer. Share this lesson with every family member and worker.

• Call 911 for collapse or serious symptoms
• Never enter to rescue a collapsed person
• Get official guidance from NIOSH and OSHA

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