Confined Space: A Guide to Industrial Work in Enclosed Areas

A confined space is a space located inside of a structure or system where work is done.

But not all internal spaces fit the definition of a confined space—the inside of an airplane hangar, for instance, would not be considered a confined space. 

To meet the definition, these three criteria must all be present:

  • The space is large enough for a person to enter it and work within it.

  • The space has limited means for entering or exiting it. 

  • The space is not meant for continuous human occupation.

Following the above criteria, when an inspector enters a giant boiler or a storage tank to inspect it, they are conducting work in a confined space. But, as already mentioned, an airplane hangar would not be considered a confined space because the space does not have limited means for entering or exiting.

These kinds of spaces can be found underground and above ground, and they’re quite common in most industrial scenarios. 

Other terms for confined spaces include a confined area, confined environment, enclosed space, or simply a confined room.


Just because confined spaces are enclosed, that doesn’t mean they’re small. For example, a scrubber—known formally as a flue gas desulfurization (FGD) unit—used to “scrub” SO2 emissions from the exhaust of coal-fired power plants might be as high as 80 feet inside. 

Industrial boilers, storage tanks, and other big industrial assets that require periodic internal inspections also present huge, cavernous spaces, all of which would be considered “confined spaces” since they meet the three criteria listed above. 

In this guide, we’ll cover how people do work in confined areas, the potential dangers of that work, and the tools used in confined space work, as well as regulatory and permitting considerations for that work.

How Can You Identify a Confined Space?

Most confined spaces are easily identifiable because they’re indoors and they meet the three criteria—they’re big enough for a person to enter, not made for continuous human occupation, and have limited means of entering/leaving.


But there are some examples that require a little bit of an imaginative stretch. 

A ditch, for example, could be considered a confined space if it’s hard to enter and leave it. Another interesting example is the inside of an airplane’s wing, which needs to be inspected periodically, and therefore can require confined space work.

An additional factor that can help identify a confined space—one that applies to both the ditch and the airplane wing, as well as to some other less common examples—is to consider the safety implications of work in the space. 

A confined space is a place that often has fatal conditions present, like noxious gasses or potentially lethal materials, but the presence of such elements is not strictly necessary to use the label "confined space."

Consider, for example, a grain bin. Grain bins present confined spaces that can be incredibly dangerous, since, if you fall into the grain, you can quickly drown. Another example are large sewer pipes, which may contain hazardous biological and/or chemical substances.


Industries Where Work Is Done in Confined Spaces

Here are the main industries where people regularly have to work in confined spaces:

Oil & Gas


  • Chimneys and smokestacks

  • Offshore rigs

  • FPSOs

  • Drilling ships

  • Jetties

  • Storage tanks

  • Refineries



  • Fermenter tanks

  • Pressure vessels and storage tanks

  • Fiberglass storage tanks

  • Heat exchangers

  • Storage silos and bins



  • Stopes

  • Ore passes

  • Crushers

  • Other areas as needed, including in equipment used to support mining operations

Power Generation


  • Coal fired boilers

  • Recovery boilers

  • Heat recovery steam generators

  • Wind turbines

  • Nuclear power plants

  • Hydro power plants

  • Chimneys and stacks

Wastewater Infrastructure


  • Pipes

  • Water outfalls

  • Storm drains

  • Manholes

  • Culverts

  • Ditches, wells, and trenches may also be a confined space when access or egress is limited (but they still have “blue sky” above)

Maritime (includes shipping yards and marine vessels)


  • Ballast tanks

  • Barges

  • Shipping containers 

  • Fish holds 

Construction (includes residential and commercial properties)


  • Crawl spaces

  • Vaults

  • Sub Cellars

  • Cold storage

  • Tunnels

Here are some other examples of confined spaces:

  • Bins

  • Silos

  • Vats

  • Hoppers

  • Water supply towers

  • Aircraft wings

  • Manure pits                                 

Confined Space Entry—Types of Work Commonly Done in These Areas

There are two types of work that are typically done in confined spaces:

  • Inspections

  • Repairs

Inspection and repairs are two parts of the maintenance process. 

Inspectors uncover potential defects within assets, and then this information is used to make maintenance determinations, including whether it should be repaired, replaced, or left alone and monitored for the time being.

For example, ballast tanks are used to control the balance of a ship while at sea by pumping sea water in and out. Because of the salinity of the sea water, these tanks commonly suffer from corrosion. 

For this reason inspectors conduct periodic inspections within these tanks by emptying them out, then entering them to look for signs of wear.

confined-space-flyability-12An inspector flies a drone inside a storage tank on an oil tanker

Just because corrosion is spotted doesn’t mean that a repair will be made right away. In some cases, the maintenance process will simply call for corrosion monitoring—keeping an eye on the defect to make sure it doesn’t progress too quickly, or to a point where the ballast tank’s integrity will become compromised and it will start to leak.

Inspections like these are crucial for ensuring the longevity of industrial assets. In industries that work with explosive materials, such as Oil & Gas, inspections are also crucial for safety, since they can help avoid an accident related to poorly maintained equipment.

When inspectors work in confined spaces they have an array of inspection techniques at their disposal.

In inspection work, these techniques are generally called Non-Destructive Testing (NDT) since they present different ways to inspect—or test—a material without having to damage it.

Here are the most common types of NDT methods that inspectors use in confined spaces:

The Dangers of Confined Area Work

Work in confined areas can be incredibly dangerous.

According to the U.S. Bureau of Labor Statistics, from 2011 to 2018 a total of 1,030 people died in the U.S. alone due to occupational injuries involving confined spaces or confined rooms.


Here are the factors that make these confined areas dangerous:

  • Atmosphere—the space could be oxygen-deficient or oxygen-enriched, or it could contain asphyxiants or traces of other noxious gasses or chemicals.

  • Chemical and biological exposures—the space could contain chemicals or bacteria dangerous for skin contact, ingestion, or inhalation. 

  • Fire hazards—the space could contain an explosive or flammable atmosphere due to flammable liquids and gasses and combustible dusts which could lead to fire or explosion.

  • Potential for engulfment—the space could contain dangers for workers to be surrounded and effectively captured by a liquid or flowable solid substance, such as grain. 

  • Mechanical and physical hazards—noise, heat/cold, radiation, vibration, electrical, structural hazards, falling debris, collapse, moving parts of equipment, inadequate lighting, entanglement, engulfment, slips, or falls.

Other dangers related to work in confined spaces:

  • Rescues—according to Canada’s Centre for Occupational Health and Safety, 60% of fatalities in confined spaces are made by would-be rescuers.

  • Work at height—inspectors and maintenance crew often have to work on scaffolding or using ropes inside confined spaces, presenting yet another potential danger to their work.


Procedure for Entering a Confined Space—Planning Ahead to Mitigate Risk

After obtaining the necessary training and permits, these are the steps typically recommended for planning a successful operation in a confined space:

1. Conduct an initial survey of the space and work 

In this survey, workers should:

  • Identify the potential hazards for work in the space.

  • Complete a risk assessment documenting the likelihood, magnitude and potential consequences of each hazard.

  • Document the number of employees that will work in the space.

  • Document potential changes or activities that could occur in the space.

2. Create and implement a plan

After the survey, workers should begin preparing the area for the work by:

  • Putting up signage and barricades—put up clear signage indicating that confined space work is underway and barricading the entry/exit points.

  • Planning for rescues and emergencies—make sure there is a clear plan for rescues and emergencies that addresses each hazard identified in the survey.

  • Clarifying the role of the standby person—identify a standby person and a plan for the specific steps they will take in the case of a rescue/emergency situation should be delineated.

3. Mitigate any hazards found

After identifying hazards, steps must be taken to mitigate them in order to prepare for entering the space. 

These steps could include:

  • The isolation of hazards.

  • Cleaning, purging, and ventilating the space.

  • Testing the atmosphere and monitoring it.

For any operation that regularly requires confined space entry, a confined space hazard assessment and control program should be established that lays out protocols for all of the above steps.


Confined Space Equipment

On recently commissioned assets, a lot of work is being done on designs to limit the need for entry into confined spaces, but in most cases, it cannot be avoided completely.

PPE (Personal Protective Equipment) for Work in Confined Spaces

The type of PPE that needs to be used will be determined in part by the specific confined space where work is planned. 

Here are examples of PPE commonly used in confined spaces:

  • Hard hats

  • Gloves 

  • Eye and face protection

  • Foot protection

  • Flame-resistant clothing (if working in a potentially explosive environment) 

  • Chemical gloves (if working where chemicals are processed/stored)

  • Fall protection harnesses (if working at height)

Equipment For Human Entry in Confined Spaces

In addition to PPE, here is some equipment commonly used to help workers get access to and work inside of confined spaces. 

Systems for confined space entry


These systems help workers with horizontal or vertical entry into areas that can be difficult to access, such as pressure vessels or manholes.



Hoists are used for lifting, lowering and positioning personnel and materials within confined space applications

Retractable devices


These devices provide workers in confined spaces with fall protection, providing bi-directional retrieval.

Equipment to Support Remote Data Collection in Confined Space Work

More and more, inspectors are reducing the need for human confined space entry by having robots take their place for specific tasks that need to be performed in these dangerous areas.

Most robotics solutions used in these areas are made for collecting visual data for the purpose of inspections. But in some instances there are robots that can not only collect data, but also perform repairs. In sewers, for example, there are new robotics tools that can actually repair leaks in pipes.

All of the robotics equipment listed below is used only for inspections—that is, for remote data collection—but as technology progresses, we’re sure to see more tools that can not only find defects, but also fix them.

Here are some of the most commonly used equipment for remote data collection in confined spaces.


A DIY or industrialized “camera-on-a-stick” is just a camera lowered from the top of a confined space. Though basic in design, this approach can represent a very cost-efficient and effective solution for collecting images without human entry. 

confined-space-flyability-19Searchcam's Camera-on-a-stick

It should be noted that these devices are limited in their access—you can only collect the imagery you can see by inserting the camera from your access point(s).

Crawler robots

Crawler robots are the tool of choice for the inspection of long spaces with a consistent geometry, such as pipes and ducts. 

confined-space-flyability-20Pipe inspection crawler from Inuktun

These robots are usually connected to the outside world by a tether, which provides power and a data link. Because they’re connected to a power source, they can be used by inspectors to perform live inspections several hundreds meters down a pipe for an unlimited time. 

However, crawlers are primarily useful in situations where there are no significant obstacles, T-junctions, or large changes in the diameter of the pipe being inspected.

Snake robots

Snake robots can enter through a manhole and be operated inside a tank. Inspectors can maneuver them around internals to access virtually any place located close enough from the entry point.

confined-space-flyability-21Snake robot from the Petrobot research project

The only drawbacks of such systems are its large weight and footprint. 

Climber robots

Climber robots use magnets to climb vertical surfaces and thus freely navigate the surface of metallic confined spaces, provided that the environment does not feature sharp angles that might block the movement. 

confined-space-flyability-22The HR-MP20 Light Weight Magnetic Climbing Robot from Helical Robotics

While some miniature versions of such climbers have been developed, most climber robots are typically heavy and expensive equipment.  

Check out our complete guide on confined space equipment here.

Confined Space Inspection Drone 

Drones are another type of equipment that is being used for inspection work in confined spaces.

But you can’t use just any drone for work in a confined area. Because of the unique limitations of these spaces, they typically call for the use of a specialized confined space inspection drone, like Flyability’s Elios 3.

confined-space-flyability-23The Elios 3, Flyability's confined space inspection drone

Unlike ground-based robots, indoor drones have a serious advantage over other mobile robotics: their versatility. Their mobility in three dimensions allows access to virtually any place, from any angle, regardless of the shape, material and geometry of the environment.

But multiple challenges await drones when flying indoors. Turbulence due to the small air volume or to drafts inside the confined space, the presence of dust, problems with signal transmission, complete darkness, and the presence of reflective surfaces, which can reduce image quality. 

And then there is the space itself—by its very nature, flying in a confined space increases the likelihood of a collision.

The Elios 3 was made to address all of these challenges. In fact, it was designed specifically for inspections in confined spaces.

The Elios 3 is surrounded by a protective cage and has collision-tolerance features, which allow inspectors to fly it in tight confined spaces to collect visual data without the fear of crashing. If the drone bumps into a wall or other surface, it can continue flying without damage.

It also has unique lighting and stability features, which allow it to collect high quality images even in the presence of dust or in pitch-black environments

confined-space-flyability-24The Elios 3 flying inside a mine

[Case study: Elios 3's 3D Mapping Helps City of Lausanne with Water Department Inspections.]

Confined Space Training and Permit Requirements

Given the dangers associated with confined spaces, most countries have developed strict standards, including training and permit requirements, for working in them.


Some of these standards are general and industry-agnostic, while others are industry-specific.

Standards serve to guide people in the correct design, safeguarding and maintenance of equipment where confined spaces are involved. During plant design, for example, the principle is to eliminate any required confined space work in the first place, but of course, this is not always practical.

Confined Space Training

Because of the dangers and complexities of confined space entry, special training is typically required in order to be certified for this kind of work. 

This training usually helps workers maximize safety by identifying hazards and establishing strong planning protocols.

A typical list of skills that might be covered in confined space training include learning how to:

  • Test the air quality for safety in the space

  • Lock and tag out connecting piping

  • Force ventilation

  • Observe workers in the space in order to make safety decisions

  • Develop a rescue plan ahead of entry

In the U.S., OSHA requires anyone who plans to enter or work around a confined space to be certified under the OSHA Confined Spaces standard 29 CFR 1910.146

To achieve this certification, OSHA requires workers to receive an 80% or higher on a written exam that demonstrates they can:

  • Determine what is a “confined space” by definition and if it is a PRCS

  • Understand the application and scope of OSHA’s confined space entry standards

  • Understand OSHA’s requirements for safely developing and running a PRCS entry program

  • Identify when to use OSHA’s alternate entry and reclassification procedures

  • Know the responsibilities of entrants, attendants, entry supervisors, and contractors

  • Understand the requirements for emergency services and rescue

  • Have basic knowledge of general use and limitation of related equipment

Confined Space Permits

Most confined spaces require workers to obtain some kind of permit before they can work in them (see the next section for exceptions).

In the U.S., figuring out whether you need a permit or not is reliant on whether you plan to work in a Permit-Required Confined Spaces (PRCS).

OSHA defines a PRCS as one that:

  • Contains or has a potential to contain a hazardous atmosphere.

  • Contains a material that has the potential for engulfing an entrant.

  • Has an internal configuration such that an entrant could be trapped or asphyxiated by inwardly converging walls or by a floor which slopes downward and tapers to a smaller cross-section.

  • Or contains any other recognized serious safety or health hazard.

Once a permit is obtained, workers have to assess hazards present in the space, then create an entry plan and a rescue plan.

For a full picture of confined space entry procedures, take a look at this PRCS Decision Flow Chart made by OSHA:


Non-Permit-Required Confined Spaces

There are some confined spaces that fit the definition of a confined space but do not require permits for work to be done there.

Some examples include:

  • Equipment closets

  • Crawl spaces under houses

  • Machinery cabinets

  • Ventilated tunnels

  • Drop ceilings

Confined Space Work Standards and Codes


NIOSH (National Institute for Occupational Safety and Health)

ASSP (American Society of Safety Professionals)



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