Working in Confined Spaces: Managing Atmospheric Hazards

Confined spaces are where essential tasks happen—maintaining pipelines, cleaning tanks, repairing utility lines underground.

But the conditions can be some of the most hazardous on any job site.

According to the Bureau of Labor Statistics, 1,030 workers died from occupational injuries involving a confined space from 2011 to 2018. Over that period, 126 workers died in confined spaces after inhaling harmful substances and another 39 workers lost their lives due to oxygen depletion.

What Is a Confined Space?

According to OSHA, a confined space is an area not primarily designed for human occupancy but large enough for workers to enter and carry out tasks. Entry and exit points are limited. You go in, do a specific job, and get out. 

Tanks, vessels, silos, storage bins, hoppers, vaults, and pits all qualify. Breweries have fermentation tanks. Restaurants have keg coolers and basement storage. Farms have grain bins and manure pits.

OSHA requires a written confined space program for any workplace with these spaces. Documented procedures need to be in place before anyone goes in. 

Permit vs Non-Permit Spaces

Permit-required confined spaces have hazardous atmospheres, engulfment risks, dangerous equipment, or other serious hazards. Non-permit spaces don’t have any of these.

Your program must cover both types. Non-permit spaces can become permit-required if conditions change.

A brewery’s fermentation tank needs a permit during active fermentation because CO₂ builds up inside. That same tank might be non-permit once it’s empty and ventilated.

Underground utility vaults, process vessels, and tanks usually need permits. Storage rooms or crawl spaces might not, unless gases accumulate or other hazards develop.

What Are the Most Dangerous Gases in Confined Spaces?

The most dangerous gases in confined spaces are carbon dioxide, nitrogen, argon, and helium because they displace oxygen without warning—they’re odorless, colorless, and can kill in minutes.

CO₂ poses a double threat. It displaces oxygen. It’s also toxic at high concentrations, causing rapid breathing, confusion, and loss of consciousness before oxygen levels even drop to dangerous territory.

Nitrogen makes up 78% of normal air, so many people assume it’s always safe. It’s not. Nitrogen displaces oxygen, and workers who enter confined spaces during nitrogen purging or near improperly isolated nitrogen systems can collapse without warning.

Argon is heavier than air and pools in low spots. Helium rises, but it still displaces oxygen. Both create invisible death traps in tanks, pits, and vessels.

Gas hazards in confined spaces include:

• Fermentation tanks: CO₂ buildup can create deadly atmospheres in minutes.
• Storage tanks and vessels: nitrogen purging displaces oxygen, which can kill workers in under 30 seconds.
• Utility vaults: welding operations generate argon clouds that settle in low areas.
• Equipment with cooling systems: helium leaks can accumulate in enclosed spaces.

You can’t see, smell, or taste these gases. Your body gives no warning until it’s already too late.

What Makes Gas Stratification So Dangerous in Confined Spaces?

Gas stratification creates invisible layers of deadly gases at different heights, and workers who feel dizzy often kneel or bend down—unknowingly moving into even denser concentrations that can kill them instantly.

Heavier gases like CO₂ and argon settle near the floor. Lighter gases like methane and helium rise to the ceiling. Normal air gets sandwiched between them, creating zones where oxygen levels change dramatically within a few feet.

A worker standing upright might breathe 21% oxygen. Drop to knee level to check a valve, and he is suddenly in 10% oxygen or pure CO₂.

This layering effect gets worse in spaces without ventilation. Gases don’t mix on their own—they separate by weight and stay that way until something disturbs them.

Here are ways that gas stratification can kill workers:

• Bending over in tanks: physical exertion increases oxygen demand right when workers enter the most toxic layer.
• Reaching for ground-level tools: maintenance workers collapse when they move from safe standing height to dangerous low zones.
• Crouching when dizzy: the natural response to feeling unwell puts workers deeper into hazardous gas layers.

What Do You Need Before Entering a Confined Space?

Before anyone enters a permit-required confined space, OSHA’s 29 CFR 1910.146 requires specific precautions—written permits, documented testing, isolation of hazards, ventilation, and safety equipment.

Pre-Entry Atmospheric Testing

Test the atmosphere at multiple levels in this exact order. Oxygen first, which must read between 19.5% and 23.5%. Combustible gases next, which must read below 10% of the lower explosive limit. Then toxic gases like CO₂, carbon monoxide, and hydrogen sulfide.

For CO₂ specifically, your readings must be below 5,000 parts per million (ppm) before entry. This threshold matches OSHA’s 8-hour Time-Weighted Average Permissible Exposure Limit (TWA PEL)—if readings reach this level, start ventilation immediately and check for leaks.

The order matters. Many gas meters need adequate oxygen to function properly, and a meter in an oxygen-deficient atmosphere will give false readings for other gases.

The entry permit lists every hazard, all required equipment, rescue procedures, and each authorized entrant by name.

How to Monitor CO₂ Levels

CO₂ monitors have three standardized alarm levels that trigger specific responses:

• AL1 at 5,000 ppm: visual alarm signals OSHA’s 8-hour limit—start ventilation immediately and check for small leaks.
• AL2 at 15,000 ppm: visual plus audible alarm means escalating danger—increase ventilation, investigate the source, and prepare for evacuation.
• AL3 at 30,000 ppm: immediate evacuation required—this matches OSHA’s Short Term Exposure Limit and can cause unconsciousness within minutes.

Learn more about what happens at various CO₂ levels.

Mount CO₂ detectors 12 inches from the floor. CO₂ settles low, and detectors at breathing height will miss it pooling near the ground.

How to Monitor Multiple Gas Hazards

In spaces with multiple gas hazards, position multiple monitors at different heights: CO₂ monitors low, oxygen monitors at breathing height, and methane or hydrogen monitors near the ceiling.

Portable monitors supplement fixed systems. They don’t replace them. Fixed monitors track long-term exposure but miss the short, deadly discharges that portable units catch immediately.

For nitrogen and argon displacement, oxygen monitors at breathing height (4-6 feet) are your primary defense. Set alarms at 19.5% for low oxygen—these invisible gases only show up as dropping oxygen levels.

Different gases settle at different heights. Heavy gases like argon pool at floor level. Light gases like helium rise to the ceiling.

Lockout/Tagout Is Mandatory

Before entering, lock out every energy source. Electrical, mechanical, pneumatic, hydraulic—anything that could start unexpectedly.

Use specific locks and tags that identify who placed them and why. A valve that opens during entry will flood the space. Equipment that starts up can trap or crush workers inside.

Ventilation runs continuously, not just before entry. Fresh air blows in at the top and exhausts from the bottom to break up gas layers.

Gas Detection Safety Solutions

WestAir partners with CO2Meter, offering gas detection safety solutions. 

Here is monitoring equipment to consider for safely working in confined spaces:

Portable detectors give you real-time protection when entering confined spaces. The PRO-10 Portable CO₂ Safety Detector provides continuous readings with a 90 dB audible alarm, visual strobe, and vibration alert. Wear it at breathing height for personal protection during entry. 

Fixed monitors provide 24/7 area coverage and automatic responses. The CM-7000 Multi-Sensor System is wall-mounted, code-compliant, and can trigger ventilation fans or connect to fire panels when CO₂ levels rise. 

For simultaneous tracking of multiple hazards, the CM-1000 Multi-Gas Sampling Data Logger measures CO₂, oxygen, and carbon monoxide together, with data logging and alarm features that simplify monitoring.

Communication gear is non-negotiable—two-way radios, air horns, or hard-wired phones keep workers connected to outside attendants. Constant contact through sight, sound, or signal can mean the difference between rescue and tragedy.

Have retrieval equipment staged and ready: harnesses, lifelines, mechanical winches, and tripods. When emergencies happen, you have seconds to react, not minutes to hunt for gear.

Block access with warning signs and barricades. Only authorized personnel should be anywhere near confined space operations. Everyone else stays clear of the area completely.

What Should Your Confined Space Training Program Include?

Your confined space training program must cover hazard recognition, atmospheric testing, equipment use, emergency procedures, and rescue protocols. And it needs continuous reinforcement because one-time onboarding isn’t enough when lives are at stake.

Training starts with recognizing what makes a space confined and potentially deadly. Workers need to identify permit-required spaces, understand atmospheric hazards, and follow OSHA requirements.

Every employee should know how to read gas monitors, interpret alarm levels, and respond correctly. They need hands-on practice with portable detectors, breathing apparatus, and communication equipment before they ever approach a confined space.

Critical Training Elements

Atmospheric testing procedures can’t just be explained. Workers must demonstrate they can test at multiple heights and understand why. They need to know oxygen drops below 19.5% can impair judgment before causing unconsciousness.

Emergency response training saves lives, but only if it’s realistic. Run drills where alarms actually sound, workers actually evacuate, and supervisors actually conduct roll calls.

Rescue training needs special attention, as many worker deaths involve would-be rescuers. 

Written program requirements must be covered thoroughly. Every worker should know where to find your confined space program, what it contains, and their specific responsibilities.

Maintaining Training Standards

Annual refreshers aren’t enough for high-risk operations. Facilities with active confined space programs should train quarterly, focusing on different scenarios each time.

Document everything: who attended, what was covered, and how competency was verified. When OSHA investigates an incident, “we covered that in training” means nothing without records.

New hazards require new training immediately. If you add nitrogen lines, install CO₂ systems, or implement other changes, update training before anyone enters affected spaces.

How Do You Create an Emergency Response Plan?

Your emergency response plan needs clear evacuation procedures, designated assembly points, roll call protocols, and specific instructions for different gas types because confused workers make fatal mistakes during real emergencies.

Start with evacuation triggers. When AL3 alarms sound at 30,000 ppm CO₂, everyone exits immediately—no investigating, no grabbing equipment, just get out.

Designate assembly points far enough from danger but close enough for quick roll calls. Missing workers might be unconscious inside, and every second counts.

CO₂ Leak Response Procedures

For CO₂ specifically, your plan must include full facility evacuation, immediate roll call, and notifying the fire department of a CO₂ leak—not just “a gas leak.”

Contact your gas supplier immediately after calling 911. They know their equipment and can help isolate the leak source faster than anyone else.

Never let anyone re-enter until meters show safe levels throughout the space. CO₂ can pool in unexpected places, and clearing one area doesn’t mean it’s all gone.

CO₂ fire extinguishers become deadly in confined spaces. The rapid CO₂ discharge can asphyxiate users before they realize the danger.

Preventing Rescue Deaths

Build this rule into your plan: no entry without proper equipment, backup, and atmospheric testing. Would-be rescuers who rush into confined spaces become victims.

Non-entry rescue comes first. Use retrieval lines, mechanical winches, and tripods to pull workers out without sending others in.

If entry rescue becomes necessary, only trained team members with supplied air and constant monitoring go in. Everyone else stays out, no exceptions.

Your local fire department needs to know your facility’s confined spaces before emergencies happen. Schedule walkthroughs, share your plans, and mark confined spaces clearly so responders can find them fast.

Practice the complete plan quarterly: alarms, evacuation, roll call, and communication with emergency services. A plan nobody remembers won’t save anybody.

The Bottom Line

Confined space safety comes down to three critical actions: test before entry with proper procedures, maintain continuous monitoring with correctly positioned equipment, and train repeatedly so everyone responds correctly when alarms are triggered.

Your investment in written programs, portable detectors, fixed monitoring systems, and continuous training protects your team and keeps you compliant.

Tyler O'Brien

Tyler is a results-driven marketing professional specializing in the industrial gases and equipment industry, bringing his 10 years of technical expertise and digital marketing acumen to the complex industrial gas B2B environment.