Jump To:

A workplace can feature numerous layouts, from open warehouses with aisles of shelves to offices with rows of cubicles. Many feature confined spaces that may make it difficult for workers to navigate. These areas can be extremely dangerous, with hundreds of injuries and deaths happening in confined spaces every year. As a result, only trained professionals should be working in confined spaces — and training is critical.

When it comes to the rules and regulations for confined spaces, workers and their employers need to know how dangerous it can be if they are not prepared. One wrong move can be the difference between life and death for a worker. In order to create a safe workplace environment, it’s crucial to understand the specific risks involved with confined spaces and the correct emergency procedures to follow if an incident occurs.

Keep reading our guide to confined spaces to learn everything you need to know.

Learn About Our Confined Space Entry Specialist Course

What Is a Confined Space?

When we think of confined spaces, it’s easy to consider them only as tiny areas present underground. However, a confined space is any wholly or partially enclosed structure an employee is likely to enter at any given moment. These spaces usually have restricted or limited entry and exit access.

A confined space can be located anywhere. While wells and sewers may be what first comes to mind, confined spaces are often silos, vats and bins. Technically, any small area where an employee may need to work could be a confined space. According to OSHA, the criteria for confined spaces is defined as such:

  1. The space has limited openings for entry and exit.
  2. The space isn’t intended for continuous human occupancy.
  3. The space is large enough for any worker to enter and conduct work.

Types of Confined Spaces

It’s essential to know not all confined spaces are the same. There are three main types of confined spaces — permit required, alternate procedure and non-permit-required spaces.

A permit-required confined space must have safety signage around the area to indicate there’s potential for danger if entered. The employees should see this signage before they enter the confined space. The workers also should be informed of all safety procedures if an accident were to occur. Essentially, permit-required confined spaces are spaces that meet the criteria of a confined space but also include one or more of the following:

  • A substance that can engulf or asphyxiate a worker.
  • A potentially hazardous atmosphere.
  • Any inwardly converging walls.
  • A downward sloping floor that tapers to a small cross-section.
  • It may contain any other life-threatening or health hazards.

An alternate permit required confined space is one that, through the proper use of ventilation, poses no other risk to the entrant. Be careful in reclassifying using this procedure as you are certifying that ALL hazards have been eliminated through the use of ventilation.

On the other hand, non-permit-required confined spaces contain none of the abovementioned dangers but should still be treated as hazardous, with a safety plan set in place if any accidents occur. These confined spaces don’t require safety signage or attendants, though notifying your employees of the confined space is still pertinent. These spaces still have limited space, which requires safety precautions. NASP finds that it is rare to have a non-permit required confined space.

Is Working in a Confined Space Hazardous?

A confined space is a concern for occupational safety and health because of the many dangers these spaces pose to the workers and the team sent to rescue them. These work areas are more hazardous when compared to other areas of the workplace because of the nature of their configuration and toxic atmospheres. The hazards commonly associated with confined spaces are as follows:

  • Toxic atmosphere: The toxic atmosphere within these confined spaces can have harmful effects on the workers inside them. Those exposed to a poisonous atmosphere may experience impairment of judgment, unconsciousness or even death if they’re in the toxic atmosphere for too long. This could include carbon monoxide and hydrogen sulfide gases.
  • Oxygen deficiency: Commonly, confined spaces lack the appropriate amount of oxygen for workers, which is an obvious hazard. Due to gases, rot, rusting and other particles in the atmosphere, oxygen deficiency can cause workers to become lightheaded and possibly faint.
  • Excess oxygen: An excess amount of oxygen present in a confined space is considered a hazard because it significantly increases the chances of fires or explosions. Some companies have mistakenly purged confined spaces with pure oxygen and the results can be disastrous.
  • Fires and explosions: If a confined space contains an explosive atmosphere, fires and explosions are possible. Therefore, the presence of flammable liquids, gasses or combustible dust causes a significant hazard because if ignited, a fire or explosion is likely to occur. Methane and hydrogen sulfide are prime examples of common explosive gases that can form within a confined space.
  • Excessive heat: Due to the contained space being enclosed, the risk of excessive heat exposure is likely. As a result, workers may experience heat stroke, becoming disoriented and unresponsive.
  • Biological agents: It’s possible for workers to be exposed to biological agents in confined spaces. For example, bacteria found in mold, fungi, fecal matter from animals or sludge can cause bacterial and viral infections.
  • Becoming trapped: Inwardly sloping walls or a tapering bottom (hopper-configuration) can make it difficult for an entrant to escape during an emergency. Also, if the only way out of the area becomes blocked or otherwise unavailable, employees can become trapped.

How Are Hazards Controlled in Confined Spaces?

Since the nature of confined spaces varies, the way you control hazards depends on the specific type of hazard. For example, you won’t utilize the same controls for a fall as you would for an explosion. Having a strategy for every possible situation is critical so you can ensure all the boxes are ticked.

Here’s a cursory look at how you can possibly make confined spaces safer when it comes to air quality and fires and explosions.

Poor Air Quality in Confined Spaces

As mentioned above, a confined space may contain a toxic atmosphere, dangerous vapors and unsafe oxygen levels that might cause harm. These atmospheric hazards are common for confined spaces because they’re places that don’t get proper air circulation or ventilation. To prevent and decrease air quality hazards, trained professionals must test the air quality within the confined space – typically oxygen first, then flammables and finally, toxics.

To properly test air quality, the trained professional should first test the air inside the confined space before anyone can enter the confined space. The trained worker should also have the proper detection equipment to perform the test and confirm oxygen levels are within safe limits (between 19.5% and 23.5% – ideally 20.8%), atmospheric toxins and flammables aren’t currently present, and the ventilation equipment is operating correctly.

There are two ventilation methods used in confined spaces. The most effective method is mechanical ventilation, which utilizes blowers, fans and other tools alike to maintain air quality. The second technique of ventilation is natural ventilation which is the usage of natural air currents. Unfortunately, on many occasions, it’s not reliable or sufficient enough to maintain air quality. Either way, both options should be considered.

Confined Space Entry Specialist (CSS)

Risk of Fires and Explosions in Confined Spaces

Both fires and explosions pose a pressing threat to workers working in a confined space. To potentially prevent these hazards, a trained professional should identify all ignition sources. The trained professional should identify these sources before the workers begin any work in the confined space.

There are various ignition sources, such as open flames, sparking of electrical equipment, combustible dust, static electricity and more. It’s also helpful to know that a fire or an explosion won’t occur unless there are three components present in the confined space — oxygen, flammable liquid and an ignition source. Removing these variables should create a safer work area. Remember, most monitors alarm at 10% of the lower explosive limit (LEL) which constitutes a prohibited condition and the entrant must leave immediately.

Why Is Working in a Confined Space More Hazardous Than Other Workplaces?

Unlike various other workspaces, confined spaces can have extremely poor air quality — and that’s the most significant hazard. Combined with potential toxins in the air, the lack of air circulation makes it difficult to breathe. This issue gets worse when it’s hot inside the area. If a worker accidentally hurts themselves or becomes trapped, the poor air quality turns rescue operations into an even tighter race against the clock.

It’s important to note that falls are one of the leading causes of confined space injuries and deaths. While falls aren’t unique to confined spaces, they can be exacerbated by the environment inside the container or compartment. In extreme scenarios, more than one incident can happen in conjunction with a fall, making the chances of injury and even death much higher.

What Should Be Done When Preparing to Enter a Confined Space?

All workers required to enter a confined space should be prepared before entry. The first point the employee should know is if the confined space is a confined space. A hazard assessment and control program is required for all confined spaces before the confined space is established.

The next question is if the work inside the confined space is necessary. There are times when employees can do the same work in a safer area. Be sure anyone assigned to work in a confined space needs to be there. If you determine the job can be completed in a safer way, you should always take that route.

After you’ve determined the job is necessary, it’s easier to take the right precautions. There are two categories of workers who operate inside the confined space — entrants and attendants. While the entrants complete the work in the confined space, attendants stand immediately outside of the entrance. As a result, the entrants have someone to alert when an issue arises, and the attendees can prevent unauthorized entry and call in the rescue team. You may also require a separate confined space supervisor and rescue service members that may be called upon to enter if someone is incapacitated within the space.

Safety Precautions in Confined Spaces

Taking the necessary safety precautions in confined spaces will decrease the chances of injury or death. There are 10 critical factors workers need to be aware of before entering the confined space and while in the confined space:

  1. Avoid entry:If a job can be done outside of the confined spaces or may not be necessary at the time, avoiding the confined space is the safest thing to do.
  2. Monitor the atmosphere: Most deaths are the result of atmospheric problems, so monitoring the toxin levels in the atmosphere of the confined space should be done frequently.
  3. Ensure space ventilation:With forced-air ventilation, you can dilute and displace toxins in the air to create a safer environment. Ensure the confined space has the best air quality possible.
  4. Offer personal protective equipment:PPE is equipment used to increase an individual’s safety while performing dangerous duties in a confined space. Using the proper PPE is essential if any hazards can’t be eliminated or controlled. The PPE must be readily available for the workers to wear.
  5. Control and eliminate hazards:Before entry, all hazards should be eliminated or at least controlled. The elimination of the danger is the preferred method, but maintaining the threat is practical, as well.
  6. Station an outside attendant:There should always be a trained worker outside the confined space to monitor entry safety, help if there’s an emergency and call for backup assistance if necessary. One of the primary roles of having a worker outside the confined space is to help if problems arise and aid in de-escalation. The outside attendee is also responsible for calling for emergency help.
  7. Be prepared for rescues:If a rescue is needed, having the equipment and personnel ready and available is critical. This group should be immediately prepared to dive into action whenever necessary. The rescue team must be adequately equipped and trained to handle any hazardous situation.
  8. Establish good lighting:Having proper lighting in a confined space is another major safety factor. If you can’t see what’s around you, it’s hard to perform the necessary work. Additionally, the entry and exit points must be well-lit to ensure workers and the rescue team can see during an emergency.
  9. Have an emergency plan:Accidents will happen, so it’s vital to be prepared by having an emergency plan in place. While emergency prevention should always be a priority, operating in a confined space requires extra attention. Knowing the specific risks involved and then devising an emergency plan is an essential factor in this circumstance.
  10. Maintain constant communication:Having effective communication is vital to any operation running smoothly. The outside attendee must maintain contact with the workers inside of the confined space. At the same time, workers should provide continuous updates to the attendee so they know what’s going on inside.

Purchase NASP’s Confined Space Entry Specialist Course

At the National Association of Safety Professionals (NASP), we provide confined space training so you’re adequately prepared to work in these areas. This course will allow you to understand confined spaces, precautions to take pre-entry, how to identify and assess hazards, proper elimination of hazards and more. The primary mission of NASP is to provide safety professionals with innovative training opportunities that exceed basic OSHA compliance.

Be prepared to work in any confined space by taking our course today.

Purchase the Confined Space Entry Specialist Course

About the Author


Pete Nemmers

Pete Nemmers serves as NASP’s Director of Training Development, bringing a wealth of expertise to the organization. With a background rooted in safety and training, Pete plays a pivotal role in shaping the training programs offered by NASP. Pete ensures that NASP remains at the forefront of safety education, equipping professionals with the knowledge and skills necessary to navigate and excel in the dynamic field of safety.
Home » Blog » Guide to Confined Spaces