What You Can’t See Can Hurt You — How To Reduce Risk In Confined Spaces

Confined spaces are an exception to the rule that you should never assume anything in life. In this case, always assume the worst -- that the space contains an unseen, unexpected hazard.

By Stephen Bayer, Product Group Manager, Portable Instruments, MSA, Pittsburgh, PA; and Stephen Bayer; Alfred W. Keiss February 1, 1998

Confined spaces are an exception to the rule that you should never assume anything in life. In this case, always assume the worst — that the space contains an unseen, unexpected hazard.

A variety of hazards can be found in a confined-space work environment, including atmospheric, physical, engulfment, corrosive, biological, and more. Atmospheric hazards are the primary contributor to accidents in confined spaces. But periodic, thorough confined space training can help save lives, prevent injuries, and reduce the chances of an OSHA violation.

OSHA’s 29 CFR 1910. 146 directs employers to establish a permit-required, confined-space program for controlling, and, where appropriate, protecting employees from permit space hazards. The employer must also regulate all entry into spaces.

This standard directs that if employees will enter permit spaces for any reason, employers must finalize responsibilities for workplace evaluation, hazard determination, employee information access, and the development of a written permit- space entry program. A major portion of the overall program includes confined-space training.

Confined spaces defined

OSHA defines a confined space as an area that:

– Is large enough for an employee to bodily enter and perform work

– Has limited or restricted means of entry or exit

– Is not designed for continuous human occupancy.

Additionally, a permit-required confined space has one or more of the following characteristics:

– Contains, or has a known potential to contain, a hazardous atmosphere

– Contains material with potential for engulfment

– Has an internal configuration such that an entrant could be trapped or asphyxiated by inwardly converging walls, or a floor which slopes and tapers to smaller sections

– Contains any other recognized serious safety or health hazard.

All confined spaces should be considered to be permit-required until proven otherwise. According to the OSHA standard, employers are required to perform an initial evaluation of any new space prior to entry.

Confined spaces come in many sizes and shapes, and are found in heavy industry, food, chemical and petroleum processing, as well as utility and communications installations and construction sites, just to name a few. These spaces often are deceiving in appearance, in that they may not “look” dangerous.

Also, it is important to note that even though a space may be determined to be nonpermit, it does not alleviate the potential atmospheric dangers surrounding that space. Different work stages can transform a space which is determined initially to be nonpermit into a permit-required space.


A trained, competent person must be thoroughly familiar with the work being performed, both within the identified confined space and in surrounding areas. Training provides workers with the skills and knowledge they need regarding confined spaces and their hazards, adds reinforcement of previously learned material, and reeducates when confusion develops or points are forgotten.

Confined-space entry training applies to all employees — including supervisors — who are required to enter an area that has restricted entry or exit, and has a potential of accumulating dangerous gases or reduced oxygen levels.

Employees must be trained prior to their initial assignments into confined spaces, before a change in assigned duties, and before changes in operations or when deviations occur in procedures. OSHA permits the annual review of canceled permits, but does not require annual retraining, although it is a good practice to follow.

Departments must establish and maintain records of employee training. Although annual refresher training is not mandated, it is a good practice. Records of confined space locations and their testing results should be maintained as part of the overall program. Results should be maintained for at least 5 yr; canceled permits must be maintained for at least 1 yr as part of the standard’s requirements for an ongoing review process.

While OSHA’s regulations clearly outline what training is required by law, keep in mind that these are minimum requirements.

Train on atmospheric testing

Atmospheric hazards are some of the most dangerous, yet frequently unnoticed, problems found in a confined space. A hazardous atmosphere is one in which workers are exposed to a risk of death, impairment of ability to self-rescue, injury, or acute illness.

As noted earlier, atmospheric testing must be performed in all confined spaces prior to initial entry. This testing informs the entrant of any potentially hazardous conditions and ensures safe entry. Testing includes the evaluation of oxygen content, flammability, and any suspected toxic exposures. Testing should be conducted with a calibrated direct-reading instrument. Atmospheric monitoring should evaluate the current status of a space, as well as verify that entry conditions remain acceptable according to the entry permit.

Train on electronic instruments and alarms

Battery-powered, direct-reading instruments are considered by many experts to be the most practical devices for conducting spot checks of a confined space atmosphere on a regular basis. Classified into two groups — single-gas or multiple-gas — these instruments typically monitor for one or a combination of the following:

– Oxygen deficiency or enrichment

– Presence of combustible gases

– Presence of toxic gases.

Depending on the capabilities of the instrument, monitoring can be conducted simultaneously for oxygen and combustible gas, or for oxygen, combustible gases, and toxic gases. These devices are commonly referred to as 2-in-1, 3-in-1, 4-in-1, or 5-in-1 alarms, depending on the number of gases that can be monitored at once. Be sure to have an atmospheric monitor that is intrinsically safe.

Regardless of the type of instrument, it is critical that regular monitoring be performed during all confined space operations. OSHA spells out three types of monitoring: initial testing, periodic testing, and continuous testing.

Initial testing should begin from outside the space using probes and/or sampling lines. This testing should proceed into all areas that workers will be expected to occupy. Also, keep in mind that travel distances and obstacles can affect worker safety if an emergency develops.

Periodic testing usually refers to reevaluating the space after workers return to it following a break or change in work shift, when there is a change in the exposure atmosphere, work changes, or different operations begin. However, periodic testing remains open to interpretation by many due to different viewpoints on what frequency is required to ensure safety.

Continuous testing is clearly understood and removes all ambiguity. It means leaving the instruments on during the entire time that workers occupy the confined space. Through continuous monitoring, workers are alerted immediately to any atmospheric changes in the confined space.

It is important to remember that, due to the difference in the vapor density of gases, testing must be done at varying levels to ensure that full atmospheric evaluation is completed. Some gases are heavier than air and tend to collect at the bottom of a confined space. Others are lighter and are usually in higher concentrations near the top of the space. Still others are the same vapor density as air and can be found in varying concentrations throughout the confined space.

Testing begins outside of a confined space for the presence of hazardous vapors or gases. Prior to opening a space, testing needs to be accomplished for gases emitting from the space. Removing covers from spaces with elevated flammable levels has generated ignition sources and subsequent explosions. Also, take into consideration where a confined entry point is located. The suspected internal atmosphere, which may consist of gases with different vapor densities, can be displaced rapidly when covers are removed from openings and air moves in. This movement of gases quickly can engulf workers in a flammable or toxic blanket while still outside of the space.

As a good rule of thumb, the space should be tested approximately every 4-ft in the direction of travel and extending out to each side. Keep in mind that gases have a habit of pocketing when left undisturbed.

Even if workers follow these guidelines, however, they should be cautious when observing the readings produced by atmospheric monitors. The instrument usually is set to monitor oxygen, flammability, and several toxic gases. The monitor is specific to these readings. If there is a change in the oxygen readout, without a change in one of the other readings, the person looking at the monitor must suspect there might be some condition present that is capable of displacing or changing the oxygen level.

This situation can be extremely dangerous if left unchallenged when there is no respirator protection or when only air-purifying respirators are used.

Calibration serves as another necessary precaution. Atmospheric monitors must have the calibration frequently checked — each day before testing a confined space is best — according to the manufacturer’s specification. A thorough inspection calibration should be performed at least annually.

Dangers of oxygen-deficient and oxygen-enriched atmospheres

OSHA has established the safe oxygen range for entry (without the use of auxiliary air supplies) to be between 19.5% and 23.5%. As long as readings remain within this range, the oxygen content is considered to be safe.

When the oxygen level dips below 19.5%, the space is considered oxygen deficient. If the space contains a simple asphyxiant, a gas that displaces oxygen, such as nitrogen, methane, or carbon dioxide, it can produce an oxygen-deficient atmosphere. The impact of oxygen deficiency in a confined space can be gradual or sudden, depending on the overall oxygen concentration, activity levels of the workers in the space, and concentration levels of other gases in the atmosphere.

When the oxygen level rises above 23.5% by volume, the atmosphere is considered oxygen enriched and prone to being unstable. As a result, the higher oxygen level, increases the likelihood and severity of flash fire or explosion.

Testing for flammability

Combustible gases, vapors, or fumes can combine with oxygen and an ignition source to create fire or explosion. Each combustible has its own lower explosive limit (LEL) and upper explosive limit (UEL), between which conditions are ripe for an explosion or fire.

Flammables are a major concern, especially in confined spaces where welding, sparking tools, lighting, or static electricity can serve as an ignition source.

Oxygen levels can affect the accuracy of readings or flammability. Any reduction in the oxygen level can result in lower flammability readings. LEL readings must be taken in the presence of acceptable oxygen readings (typically, sensor readings set at 10% oxygen, or higher) to ensure the accuracy of the LEL read-out. Testing for flammability must be done to ensure the atmosphere is beneath 10% of the LEL.

Another safety factor to keep in mind is that some flammable gases are doubly dangerous because they also are poisonous. Remember, though, that the LEL of flammable gases is much higher than the level at which the gas is toxic.

When it comes to atmospheric hazards in confined spaces, it’s what you can’t see that can hurt you. That’s why it is always prudent to thoroughly train your employees on the proper techniques and use of atmospheric monitoring instruments.

— Edited by Cheryl M. Firestone, Senior Editor, 847-390-2657, cfirestone@cahners.com

Key concepts

OSHA directs employers to establish a permit-required, confined space program that includes training.

Always assume that a confined space contains an unseen, unexpected hazard.

Test up, down, and all around before entering a confined space.

Training and anticipation are keys to saving lives

Here are several practical tips that help develop a safer confined space plan.

1 Always keep an open mind. Expect changes in atmospheric conditions.

2 Check instrument calibration daily before testing atmospheric conditions.

3 Never assume that the confined space has been locked out properly.

4 Never assume there are no hazards in a space. Gas may leak into the confined space from somewhere else.

5 Always test up, down, and all around. Gases react differently, and can be lingering in different parts of a confined space.

6 Always proceed with caution. Example: A worker dropped a tool into an opening that, unbeknownst to him, was inert with nitrogen. When he leaned over to pick it up, his diaphragm was compressed against the wall, causing him to exhale. When he stood upright, he inhaled the inert gas, causing him to lose consciousness.

7 Appoint one experienced, competent person to be in charge of your respiratory-protection program, including confined-space atmospheres. With so many different hazards in the workplace, safety directors cannot be expected to be jacks-of-all-trades.

Training requirements

OSHA’s 1910.146 requires that all employees who enter restricted spaces receive training and information on the following topics:

– Expected duties of the attendant, authorized entrant, and entry supervisor

– Contents, location, and availability of the organization’s confined space entry plan

– Contents, location, and availability of the department plan

– Atmospheric conditions

– Entry/exit access

– Engulfment conditions

– Specific confined space entry procedures

– Operating and rescue procedures

– Confined spaces entry permit forms and authorization

– Test equipment procedure and calibration/maintenance schedule.

Always assume the worst in a confined space!

This is the first lesson all workers who deal with confined spaces must learn. Otherwise, the results can be catastrophic, as these real-life scenarios illustrate.

While dredging sludge from a sewage lagoon, three workers entered the compartments of a semi-tanker unit to clean them. One of the employees died when he was overcome by a combination of toxic gases and an oxygen-deficient atmosphere within the tank. The employer was cited by OSHA for alleged willful violations of the Permit-Required Confined Space Standard (29 CFR 1910.146), including no training, no formal evaluation of the hazard potential, no written program or procedures, and no written entry permit procedures.

A 45-yr-old mechanic for a trucking company climbed inside a 24-in. hatch on top of a tanker to clean up leftover water so the truck could be reloaded with asphalt for hauling later in the day. The mechanic was overcome by hydrogen sulfide, a byproduct of heating asphalt, and died. After about 30 min, the truck’s driver noticed the mechanic was taking an unusually long time. He looked into the hatch, saw the mechanic sprawled on the bottom of the tank, and called for help. A coworker rushed over and climbed through the hatch in an attempt to rescue him. The 34-yr-old would-be rescuer also succumbed to the fumes and died.

Physiological effects of oxygen

Oxygen, % Physiological effect

19.5 – 16 Possible disorientation

16 – 12 Increased breathing rate; accelerated heart-beat; impaired attention, thinking, and coordination

14 – 10 Faulty judgment and poor muscular coordination; muscular exertion causing rapid fatigue; intermittent respiration

10 – 6 Nausea, vomiting; inability to perform vigorous movement, or loss of the ability to move; unconsciousness, followed by death

Below 6 Difficulty breathing; convulsive movements; death in minutes

Lack of confined space planning and training costs lives

The following statistics were compiled during an investigation of 39 workplace fatalities in 17 states caused by improper confined space entry:

– 95% of the entries were authorized by supervisors

– 85% of events were in the presence of a supervisor

– 43% of the victims were would-be rescuers

– 31% of companies with fatalities had written confined space entry procedures

– 29% of fatalities were supervisors

– 15% of the fatalities had completed confined space entry training

– None of the fatalities followed written procedures

– None of the spaces was evaluated or tested prior to entry

– None of the spaces was ventilated

– None of the companies suffering fatalities had a rescue plan.

Source: NIOSH, Division of Safety Research