Confined Space: A Guide to Industrial Work in Enclosed Areas

A confined space is an area within a structure or system where work is performed. However, not all enclosed spaces qualify as confined spaces. For instance, the inside of an airplane hangar would not typically be considered a confined space due to its open access and lack of restricted entry.

To qualify as a confined space, three key criteria must be met:

• The space is large enough for a person to enter and work within it.
• The space has limited means of entry and exit.
• The space is not designed for continuous human occupation.

For example, when an inspector enters a large boiler or storage tank for inspection, they are working in a confined space. On the other hand, an airplane hangar does not meet these criteria because it allows for easy access and egress.

Confined spaces can be found both underground and above ground, and they are common in various industrial settings. Other terms used to describe these areas include confined area, confined environment, enclosed space, or simply a confined room.

Even though confined spaces are enclosed, they can be quite large. For instance, a flue gas desulfurization (FGD) unit, commonly known as a scrubber, can reach up to 80 feet in height. Similarly, industrial boilers and storage tanks that require regular internal inspections often create vast, enclosed spaces that are classified as confined spaces.

This guide will explore how people perform work in confined areas, the potential dangers involved, the tools used in such work, and the regulatory and permitting considerations required for safe operations.

How to Identify a Confined Space

Most confined spaces are straightforward to identify since they are indoors and meet the three defining criteria—being large enough for entry, not meant for continuous use, and having limited access. However, some examples may require a bit more thought.

For example, a ditch could be considered a confined space if it's difficult to enter and exit. Another interesting case is the inside of an airplane wing, which requires periodic inspections and thus involves confined space work.

An additional factor to consider when identifying a confined space is the safety implications of working in it. While the presence of hazardous materials is not strictly necessary, confined spaces often pose risks like noxious gases, engulfment hazards, or mechanical dangers.

Consider a grain bin, which can be extremely dangerous if someone falls into it and drowns. Large sewer pipes also present significant risks due to the presence of harmful biological or chemical substances.

Industries That Involve Work in Confined Spaces

Here are the main industries where workers regularly perform tasks in confined spaces:

Oil & Gas

• Chimneys and smokestacks
• Offshore rigs
• FPSOs
• Drilling ships
• Jetties
• Storage tanks
• Refineries

Chemical

• Fermenter tanks
• Pressure vessels and storage tanks
• Fiberglass storage tanks
• Heat exchangers
• Storage silos and bins

Mining

• 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

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

Additional examples of confined spaces include bins, silos, vats, hoppers, water supply towers, aircraft wings, and manure pits.

Confined Space Entry – Common Types of Work

There are two primary types of work conducted in confined spaces:

• Inspections
• Repairs

These tasks are part of the maintenance process. Inspectors identify potential issues, and this information is used to determine whether repairs are needed, replacements are required, or if the issue should be monitored over time.

For example, ballast tanks on ships are used to control balance by pumping seawater in and out. Due to the high salinity of seawater, these tanks are prone to corrosion. Inspectors conduct periodic inspections by emptying the tanks and entering them to check for signs of wear.

An inspector flies a drone inside a storage tank on an oil tanker

Discovering corrosion doesn't always mean immediate repair. Sometimes, the maintenance plan includes monitoring the defect to ensure it doesn’t worsen to the point of compromising the tank’s integrity.

Inspections like these are crucial for ensuring the longevity of industrial assets. In industries involving explosive materials, such as Oil & Gas, inspections are also vital for safety, as they help prevent accidents caused by poorly maintained equipment.

When working in confined spaces, inspectors have a range of inspection techniques at their disposal. These are generally referred to as Non-Destructive Testing (NDT), as they allow for the inspection of materials without causing damage.

Some of the most common NDT methods used in confined spaces include:

• Visual Testing (VT)
• Acoustic Emission Testing (AE)
• Eddy Current Testing (ET)
• Leak Testing (LT)
• Dye Penetrant Testing (PT)
• Magnetic Particle Testing (MT)
• Radiography Testing (RT)
• Ultrasonic Testing (UT)

The Dangers of Working in Confined Spaces

Work in confined spaces can be extremely hazardous. 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 rooms.

Several factors contribute to the danger of confined spaces:

• Atmosphere – The space might be oxygen-deficient, oxygen-enriched, or contain asphyxiants or toxic gases.
• Chemical and biological exposure – The space could contain harmful chemicals or bacteria that pose risks through skin contact, ingestion, or inhalation.
• Fire hazards – The space might contain flammable atmospheres due to liquids, gases, or combustible dusts, leading to fires or explosions.
• Engulfment risk – The space could trap workers in liquids or flowable solids, such as grain.
• Mechanical and physical hazards – These include noise, heat/cold, radiation, vibration, electrical hazards, structural risks, falling debris, collapses, moving parts, poor lighting, entanglement, and slips or falls.

Additional dangers associated with confined space work include:

• Rescue operations – According to Canada’s Centre for Occupational Health and Safety, 60% of fatalities in confined spaces occur among those attempting rescues.
• Working at height – Inspectors and maintenance crews often work on scaffolding or using ropes inside confined spaces, adding another layer of risk.

Procedure for Entering a Confined Space – Planning Ahead to Reduce Risk

After obtaining the necessary training and permits, here 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 potential hazards in the space.
• Complete a risk assessment documenting the likelihood, magnitude, and potential consequences of each hazard.
• Document the number of employees who will work in the space.
• Document any changes or activities that could occur in the space.

2. Create and implement a plan

After the survey, workers should prepare the area for work by:

• Setting up signage and barricades to indicate that confined space work is underway and to secure entry/exit points.
• Planning for rescues and emergencies, ensuring there is a clear plan addressing each identified hazard.
• Clarifying the role of the standby person, including specific steps they will take in case of a rescue or emergency.

3. Mitigate any identified hazards

Once hazards are identified, steps must be taken to mitigate them before entering the space. These steps may include:

• Isolating hazards.
• Cleaning, purging, and ventilating the space.
• Testing and monitoring the atmosphere.

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

Confined Space Equipment

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

Personal Protective Equipment (PPE) for Confined Space Work

The type of PPE required depends on the specific confined space where work is planned. Common PPE used in confined spaces includes:

• Hard hats
• Gloves
• Eye and face protection
• Foot protection
• Flame-resistant clothing (for potentially explosive environments)
• Chemical gloves (for handling chemicals)
• Fall protection harnesses (for working at height)

Equipment for Human Entry in Confined Spaces

In addition to PPE, here are some common pieces of equipment used to help workers access and work inside confined spaces:

Systems for confined space entry

These systems assist workers with horizontal or vertical entry into difficult-to-access areas, such as pressure vessels or manholes.

Hoists

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

Retractable devices

These devices provide fall protection for workers in confined spaces, allowing for bi-directional retrieval.

Equipment for Remote Data Collection in Confined Space Work

Increasingly, inspectors are reducing the need for human entry by using robots to perform specific tasks in dangerous confined spaces. Most robotics solutions are designed for visual data collection during inspections, although some can also perform repairs. For example, in sewers, new robotic tools can actually repair pipe leaks.

All the robotics equipment listed below is used for inspections, i.e., remote data collection. As technology advances, we can expect to see more tools that not only detect defects but also fix them.

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

Camera-on-a-Stick

A "camera-on-a-stick" is a simple device used to lower a camera into a confined space. Though basic in design, this approach can be very cost-effective and efficient for collecting images without requiring human entry.

Searchcam's Camera-on-a-stick

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

Crawler Robots

Crawler robots are ideal for inspecting long spaces with consistent geometry, such as pipes and ducts. They are usually connected to the outside world via a tether, providing power and a data link. Because they're connected to a power source, they can be used for live inspections several hundred meters down a pipe for an unlimited time.

Pipe inspection crawler from Inuktun

However, crawlers are primarily useful in situations with no significant obstacles, T-junctions, or large diameter changes.

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 close enough to the entry point.

Snake robot from the Petrobot research project

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

Climber Robots

Climber robots use magnets to climb vertical surfaces and navigate metallic confined spaces, provided the environment doesn't have sharp angles that could block movement.

The HR-MP20 Light Weight Magnetic Climbing Robot from Helical Robotics

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

Check out our complete guide on confined space equipment here.

Confined Space Inspection Drone

Drones are another type of equipment used for inspection work in confined spaces. However, not just any drone can be used. Due to the unique challenges of these spaces, specialized confined space inspection drones, like Flyability’s Elios 3, are typically required.

The Elios 3, Flyability's confined space inspection drone

Unlike ground-based robots, indoor drones have a major advantage: their versatility. Their mobility in three dimensions allows access to virtually any location, from any angle, regardless of the shape, material, or geometry of the environment.

However, multiple challenges await drones when flying indoors. Turbulence due to small air volume or drafts inside the confined space, the presence of dust, signal transmission problems, complete darkness, and reflective surfaces that reduce image quality are all potential issues.

Additionally, the confined space itself increases the likelihood of collisions. The Elios 3 was specifically designed to address these challenges. It features a protective cage and collision-tolerance features, allowing inspectors to fly it in tight spaces to collect visual data without the fear of crashing. If the drone bumps into a wall or surface, it can continue flying undamaged.

It also has unique lighting and stability features, enabling high-quality image capture even in dusty or pitch-black environments.

The 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 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 the need for confined space work wherever possible, but this is not always practical.

Confined Space Training

Due to the dangers and complexities of confined space entry, special training is usually required to be certified for this kind of work. This training helps maximize safety by identifying hazards and establishing strong planning protocols.

A typical list of skills covered in confined space training includes 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 to make safety decisions.
• Develop a rescue plan before entry.

In the U.S., OSHA requires anyone planning 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, workers must pass a written exam with a score of 80% or higher, demonstrating their ability to:

• Determine what constitutes a “confined space” 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 limitations of related equipment.

Confined Space Permits

Most confined spaces require workers to obtain a permit before they can work in them (see the next section for exceptions). In the U.S., determining whether a permit is needed depends on whether the space is classified as a Permit-Required Confined Space (PRCS).

OSHA defines a PRCS as one that:

• Contains or has the potential to contain a hazardous atmosphere.
• Contains a material that has the potential for engulfing an entrant.
• Has an internal configuration that could trap or asphyxiate an entrant due to inwardly converging walls or a sloping floor.
• Or contains any other recognized serious safety or health hazard.

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

For a full understanding of confined space entry procedures, refer to this PRCS Decision Flow Chart made by OSHA:

Non-Permit-Required Confined Spaces

Some confined spaces fit the definition of a confined space but do not require permits for work to be done there. Examples include equipment closets, crawl spaces under houses, machinery cabinets, ventilated tunnels, and drop ceilings.

Confined Space Work Standards and Codes

OSHA

• Confined Spaces
• Appendix A: Permit-required Confined Space Decision Flow Chart
• Appendix B: Procedures for Atmospheric Testing
• Appendix C: Examples of Permit-required Confined Space Programs
• Appendix D: Confined Space Pre-Entry Checklist
• Appendix E: Sewer System Entry
• Appendix F (Non-Mandatory): Rescue Team or Rescue Service Evaluation Criteria

NIOSH (National Institute for Occupational Safety and Health)

• NIOSH information on Confined Spaces
• NIOSH Preventing Entrapment and Suffocation Caused by the Unstable Surfaces of Stored Grain and Other Materials
• NIOSH Preventing Occupational Fatalities in Confined Spaces
• NIOSH Guide to Safety in Confined Space

ASSP (American Society of Safety Professionals)

• ASSP Confined Spaces Standard ANSI/ASSP Z117.1

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