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Confined Space Air Monitoring

Air in a bin, pit, tank or silo can be unsafe even when it looks and smells normal. Monitoring is one tool within a full entry program, not a shortcut.

Why does air in a confined space need checking?

Confined spaces such as manure pits, tanks, silos and bins can lack oxygen, hold toxic gases, or build up flammable vapors. Your senses cannot reliably detect these conditions, and some of them can overcome a person within moments.

That is why official programs treat testing the atmosphere as a basic requirement before and during entry. It tells trained people whether the space is safe to enter or needs ventilation first.

Warning: do not rely on smell, appearance or a brief look to judge air quality. Many farm incidents in confined spaces have involved people who believed the space was fine. Near misses deserve attention. If a monitor alarmed unexpectedly or someone felt dizzy near a storage, talk it through with everyone involved and ask an expert what it means. Small warnings are free lessons.

What can monitors detect?

Different monitors are made for different things. Many portable units measure oxygen along with selected toxic and flammable gases, and some are built for specific hazards such as hydrogen sulfide. What a given device detects depends on its sensors.

Check the manufacturer's literature to learn what your device can and cannot sense. A monitor that does not read a gas will not warn you about it, and a silent device is not proof of safety.

Alarm settings and acceptable levels come from official sources and the manufacturer, and this guide does not state numbers. Ask a qualified safety professional.

Is a monitor enough on its own?

No. A monitor is one part of a confined space entry program that also includes identifying spaces, written procedures, ventilation, lockout of equipment, a trained attendant outside, communication and a rescue plan.

OSHA publishes rules for confined spaces in general industry and construction, and agricultural settings may be treated differently. Contact OSHA or your state agency to learn how requirements apply to your operation.

Even where rules do not require it, following a full program is the sound approach for the safety of everyone involved.

How do you use monitors responsibly?

Learn from the manufacturer's manual and from hands-on training. Devices need to be tested before use, calibrated and maintained on a schedule, and used by people who know how to read them.

Check the atmosphere from outside the space first, using proper sampling methods taught in training, and continue to monitor while people work.

Store the device clean and dry, keep batteries charged and replace sensors as directed. A neglected device can fail silently.

• Bump test or calibrate as the manufacturer directs
• Charge or replace batteries before each job
• Know what each sensor reads and its limits
• Record readings and who was present
• Retire or service damaged equipment

What does monitoring not do?

A monitor does not make a space safe. It cannot protect against engulfment in grain, mechanical hazards, heat or electrical hazards. It also cannot replace ventilation, lockout or an attendant.

Rescue is separate. Never enter to rescue someone unless you are trained and equipped, since would-be rescuers have often become victims.

If a person is down in a space, call 911 and let trained responders handle the entry.

Who can help you build a program?

Ask your extension safety specialist, state or federal occupational safety office, insurance carrier, and local fire department. Agricultural safety organizations and some community colleges provide training.

If you hire custom workers for tank or pit work, ask about their entry program and equipment before they begin.

Have everyone on the farm know that confined spaces are off-limits unless the program is followed.

What should you do if the monitor alarms?

Leave the space immediately and get to fresh air. Do not turn back to gather tools. Keep others out, and follow your emergency plan.

Call 911 if anyone is affected, and give responders the location and the type of space. Anyone exposed should be evaluated by medical professionals.

Write down the plan. A short, written list that names who is trained, where the device is kept, how often it is tested and what the emergency steps are makes it far easier to follow the plan on a busy day. Review it every year and after any near miss.

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