What is a Confined Space?

Worker descending into confined space.

The time to learn about confined spaces is well before you find yourself descending through a manhole.

We’ve covered many other elements of confined space work in the past: from specialized equipment, to rescue plans, and underappreciated roles in confined space supervision.

Missing in all this is a discussion that seems so basic that it’s easy to forget how necessary it is: what is a confined space?

The answer, from the Occupational Safety and Health Administration (OSHA) isn’t so straightforward as one might assume. Enter one and it soon becomes apparent that what’s called a confined space can be downright cavernous on the inside.

Being able to identify which job sites are confined spaces is the first step in your safety. To go in with misconceptions will leave your crew exposed to hazards and without the right tools, training, and planning to protect themselves.

Many aspects of confined space safety seem like basic common sense when you really look at them. But those basics can be life-saving.

With that in mind, we want to examine what makes a confined space, the hazards that can exist in confined spaces, and some examples of confined spaces you may encounter on the job.

What is a Confined Space?

An open manhole.

Manholes are one of the most ubiquitous and obvious confined spaces.

According to OSHA, a confined space is any work area that is large enough for a worker to enter and operate in, is not designed for continuous occupancy, and has limited or restricted means of entry or exit.

Beyond that, some spaces are classified as “permit-required” confined spaces, which are spaces that have (or could have) a hazardous atmosphere, contains material which could engulf an entrant, could trap or asphyxiate an entrant, or contains any other recognized health and safety hazard.

Let’s break this definition down piece by piece:

  • Any work area that is large enough for a worker to enter and operate in. This is probably the most straightforward aspect of this definition. If you can enter the space and work therein, you just may have a confined space.
  • An area not designed for continuous occupancy. The confined space is not an office or a permanent workstation. It lacks the facilities to support people doing normal work, or its primary function must be interrupted to allow entrance.
  • An area that has limited or restricted means of entry or exit. If it has one entrance or exit, or if entrance requires entrants to descend into an area, it could well qualify as a confined space.

If your workspace meets all three of the above criteria, it is a confined space. If it also meets any of the following, it is a permit-required confined space:

  • Has or could have a hazardous atmosphere
  • Contains material which could engulf an entrant
  • Could trap or asphyxiate an entrant
  • Contains any other recognized health and safety hazard

But we’ll discuss those in a minute.

Examples of Confined Spaces

Reading the above, one may have some examples of confined spaces coming to mind. And there are definitely obvious cases: manholes, utility vaults, sewers, and pipes are common confined spaces where even commuters can observe ongoing work.

There are, however, multiple examples of confined spaces that may not occur to most people at first.

Grain silos.

These large silos may be huge, but they are confined spaces.

For instance, silos qualify as confined spaces, despite not being what people would typically think of as “small” or “cramped.” Since grain or most things stored in silos can engulf entrants, they technically qualify as confined spaces.

Confined spaces don’t need to have a roof. If access or egress is limited, a ditch or trench qualifies as a confined space, even if it’s open to the sky. Imagine needing to evacuate that trench through a narrow exit for a visceral reminder of how confined it can be.

When evaluating any worksite, it’s crucial that you and your crew don’t just rely on assumptions. Go through OSHA’s criteria for what makes a confined space to ensure that all entrants are thoroughly protected, and everyone on site is properly trained.

Unless you and your crew know what to look for, many confined spaces are not obvious. And it is not the obvious dangers, but frequently the unanticipated ones that put workers most at risk. Thorough planning prevents accidents, injuries, and fatalities.

Confined Space Hazards

The factors that differentiate a confined space from a permit-required confined space come down to the hazards present in the area.

If hazards are not present or will be eliminated before work begins, then it is a normal confined space. If those hazards are present but controlled, then the work area qualifies as a permit-required confined space.

Before work can take place in a permit-required confined space, the employer must effectively identify it, most often by posting signs. Written plans must be made for operations that will take place before anyone enters the permit-required confined space.

We’ve outlined the steps to creating these plans in a previous post, and it’s well worth taking the time to go over the process again and again.

Of the hazards that could potentially exist in a confined space, the most straightforward is toxic gas. Clean air must be circulated into the confined space to purge any harmful substances from the atmosphere, and entrants must be equipped with a gas monitor.

Testing the atmosphere of a confined space.

Checking confined spaces for hazards like toxic gas is necessary for work to take place.

More on the best practices and hazards surrounding toxic gas in confined spaces can be found in one of our previous posts.

Substances that can engulf or asphyxiate an entrant can include things like grain, piles of which can fall, causing a sort of avalanche burying the entrant. Additionally, an entrant can fall into piles and asphyxiate.

Sometimes the design of the confined space itself is the danger. Worksites with inward-converging walls or a downward-sloping floor that lead to narrow passages can easily trap a worker, causing traumatic injury or asphyxiation.

These are horrifying scenarios to be sure, and we don’t relish discussing them. But they are part of the real and constant dangers of confined space work. Only by talking about them frankly can we hammer home what exactly is at stake here.

You can’t successfully ensure confined space safety if you don’t understand the nature of confined spaces themselves. We hope that this guide serves that purpose and makes you and your crews safer.

Have a question you'd like answered? Please call us at 800-525-8460 or