605 Confined Space Safety

Glossary

A

• Acceptable entry conditions. The conditions that must exist in a permit space, before an employee may enter that space, to ensure that employees can safely enter into, and safely work within, the space.
• Access. The means by which a worker enters a confined space. Safe access is critical for confined space operations, requiring proper equipment and clear entry points.
• Ammonia. A colorless gas with a pungent odor, often used in industrial processes. In confined spaces, exposure to high levels of ammonia can cause irritation to the eyes, nose, and throat, as well as respiratory distress.
• ANSI (American National Standards Institute). A private, non-profit organization that coordinates the development of voluntary consensus standards in the U.S. These standards cover a broad range of industries, including safety practices for confined spaces. ANSI works to ensure that the products, services, processes, and systems are safe, reliable, and consistently applied. Standards related to confined space safety are designed to prevent accidents and promote best practices in assessing, entering, and working in confined spaces.
• Attendant. An individual stationed outside one or more permit spaces who assesses the status of authorized entrants and who must perform the duties specified in § 1926.1209.
• Atmospheric Hazard. A dangerous condition found in confined spaces that can result from the presence of hazardous gases, insufficient oxygen, or the buildup of toxic fumes. These conditions can pose immediate threats to workers' health or safety, such as asphyxiation, explosions, or poisoning. Testing the atmosphere before entry is critical in ensuring that these hazards are identified and controlled.
• Attendant. A worker stationed outside a confined space who monitors conditions and assists in the event of an emergency. The attendant is responsible for communication with the entrants and ensuring that rescue operations can be initiated if needed.
• Authorized Person. A worker who has been approved by their employer to enter a confined space, having received appropriate training on the hazards and safety procedures involved.

B

• Barrier. A physical obstruction that blocks or limits access.
• Benzene. A colorless or light yellow chemical that is commonly found in industrial processes. Benzene is a known carcinogen and can pose a significant health risk to workers in confined spaces, especially in oil and gas facilities.
• Blanking or blinding. The absolute closure of a pipe, line, or duct by the fastening of a solid plate (such as a spectacle blind or a skillet blind) that completely covers the bore and that is capable of withstanding the maximum pressure of the pipe, line, or duct with no leakage beyond the plate.
• Bleach. A chemical compound used primarily for cleaning and disinfecting. In confined spaces, bleach can release toxic fumes when combined with other chemicals, creating hazardous conditions for workers.

C

• Carbon Monoxide (CO). A colorless, odorless gas that can be deadly in confined spaces. It is often produced by combustion processes and poses a significant risk of poisoning when inhaled in high concentrations.
• Carbon Tetrachloride. A toxic chemical often used in industrial applications. Exposure to carbon tetrachloride in confined spaces can lead to serious health effects, including liver and kidney damage.
• CDC (Centers for Disease Control and Prevention). A federal agency under the U.S. Department of Health and Human Services tasked with protecting public health and safety. The CDC provides guidance on occupational safety, including recommendations for confined space safety to prevent work-related illnesses and injuries. They collaborate with other agencies like NIOSH and OSHA to improve workplace safety standards.
• Chlorine. A highly toxic gas that can be used in water treatment and other industrial processes. Chlorine exposure in confined spaces can cause severe respiratory problems and irritation to the skin and eyes.
• Combustible Atmosphere. An atmosphere in a confined space that contains enough vapor, gas, or dust that can ignite when exposed to a source of ignition. Workers in such environments must take precautions to prevent fires or explosions.
• Combustible Dust. Finely divided particles that can become airborne and pose a fire or explosion hazard in confined spaces. Common materials that produce combustible dust include grain, metal, wood, and chemicals.
• Competent Person. A person designated by their employer who has the training and knowledge to identify confined space hazards and who is authorized to take prompt corrective action to mitigate those hazards.
• Confined space. A confined space is a space that:
1. Is large enough and so configured that an employee can bodily enter it;
2. Has limited or restricted means for entry and exit; and
3. Is not designed for continuous employee occupancy.
• Control. The action taken to reduce the level of any hazard inside a confined space using engineering methods (for example, by ventilation), and then using these methods to maintain the reduced hazard level. Control also refers to the engineering methods used for this purpose. Personal protective equipment is not a control.
• Controlling Contractor. The employer that has overall responsibility for construction at the worksite. Note. If the controlling contractor owns or manages the property, then it is both a controlling employer and a host employer.

D

• Direct-Reading Testing. The use of handheld or portable devices to immediately measure conditions like oxygen levels or the presence of toxic gases in confined spaces. Direct-reading instruments provide real-time data to help workers assess hazards.
• Double block and bleed. The closure of a line, duct, or pipe by closing and locking or tagging two in-line valves and by opening and locking or tagging a drain or vent valve in the line between the two closed valves.

E

• Early-warning system. The method used to alert authorized entrants and attendants that an engulfment hazard may be developing. Examples of early-warning systems include, but are not limited to: Alarms activated by remote sensors; and lookouts with equipment for immediately communicating with the authorized entrants and attendants.
• Egress. The means of exiting a confined space safely. Proper egress is essential for ensuring that workers can escape quickly in the event of an emergency.
• Emergency. Any occurrence (including any failure of power, hazard control or monitoring equipment) or event, internal or external, to the permit space that could endanger entrants.
• Enclosed Space. A specific type of confined space that is entirely or mostly enclosed, such as tanks or vaults, where entry and exit are restricted. Enclosed spaces may present additional hazards due to the limited air circulation.
• Engulfment Hazard. The risk in a confined space where a person may be surrounded or buried by materials such as grain, sand, or liquids, leading to injury or death.
• Entry Permit System. A system required by OSHA when workers enter permit-required confined spaces. The permit system ensures that proper safety measures are in place before entry, such as hazard identification, isolation of energy sources, atmospheric testing, and emergency preparedness. The permit includes specific details about the space, work to be performed, hazards involved, and protective measures. It must be reviewed and approved before entry.
• Entry Procedures. The set of protocols workers must follow before entering a confined space. These procedures include obtaining a permit, testing the atmosphere, and ensuring that all necessary safety equipment and personnel are in place.
• Entry Supervisor. A person responsible for overseeing confined space entry operations, ensuring that safety procedures are followed, and that all personnel involved are aware of the hazards. The supervisor verifies that the space is safe for entry before work begins.
• Explosive Range. The range of concentrations of a flammable gas or vapor in air that will ignite if exposed to an ignition source. The lower explosive limit (LEL) and upper explosive limit (UEL) define the boundaries of this range.

F

• Flammable Atmosphere. An atmosphere in a confined space that contains sufficient concentrations of flammable vapors or gases to ignite if a spark or flame is introduced. Proper ventilation and hazard controls are essential to prevent explosions or fires.
• Flammable Range. The concentration range of a gas or vapor in air that is flammable. It is defined by the lower flammability limit (LFL) and the upper flammability limit (UFL). Outside of this range, the mixture is either too lean (below LFL) or too rich (above UFL) to ignite.

G

• Gas Detection. The use of instruments to monitor and identify hazardous gases in a confined space, such as toxic or flammable gases. Continuous gas detection is crucial for worker safety.

H

• Hazard. A physical hazard or hazardous atmosphere. See definitions below.
• Hazardous atmosphere. An atmosphere that may expose employees to the risk of death, incapacitation, impairment of ability to self-rescue (that is, escape unaided from a permit space), injury, or acute illness from one or more of the following causes:
1. Flammable gas, vapor, or mist in excess of 10 percent of its lower flammable limit (LFL).
2. Airborne combustible dust at a concentration that meets or exceeds its LFL. Note: This concentration may be approximated as a condition in which the combustible dust obscures vision at a distance of 5 feet (1.52 meters) or less.
3. Atmospheric oxygen concentration below 19.5 percent or above 23.5 percent.
4. Atmospheric concentration of any substance for which a dose or a permissible exposure limit is published in subpart D of this part (Occupational Health and Environmental Control), or in subpart Z of this part (Toxic and Hazardous Substances), and which could result in employee exposure in excess of its dose or permissible exposure limit. Note: An atmospheric concentration of any substance that is not capable of causing death, incapacitation, impairment of ability to self-rescue, injury, or acute illness due to its health effects is not covered by this definition.
5. Any other atmospheric condition that is immediately dangerous to life or health. Note: For air contaminants for which OSHA has not determined a dose or permissible exposure limit, other sources of information, such as Safety Data Sheets that comply with the Hazard Communication Standard, § 1926.59, published information, and internal documents can provide guidance in establishing acceptable atmospheric conditions.
• Host employer. The employer that owns or manages the property where the construction work is taking place. Note: If the owner of the property on which the construction activity occurs has contracted with an entity for the general management of that property, and has transferred to that entity the information specified in § 1926.1203(h)(1), OSHA will treat the contracted management entity as the host employer for as long as that entity manages the property. Otherwise, OSHA will treat the owner of the property as the host employer. In no case will there be more than one host employer.
• Hot work. Operations capable of providing a source of ignition (for example, riveting, welding, cutting, burning, and heating).
• Hydrochloric Acid. A corrosive acid used in various industrial processes. In confined spaces, exposure to hydrochloric acid vapors can cause severe respiratory and skin irritation, and workers must take precautions to avoid contact.
• Hydrogen Sulfide (H₂S). A colorless gas with a characteristic "rotten egg" smell, often found in oil and gas operations. In confined spaces, hydrogen sulfide can be deadly even in small concentrations, as it is highly toxic and can cause respiratory failure.

I

• Immediately dangerous to life or health (IDLH). Any condition that would interfere with an individual's ability to escape unaided from a permit space and that poses a threat to life or that would cause irreversible adverse health effects. Note: Some materials—hydrogen fluoride gas and cadmium vapor, for example—may produce immediate transient effects that, even if severe, may pass without medical attention, but are followed by sudden, possibly fatal collapse 12-72 hours after exposure. The victim "feels normal" after recovery from transient effects until collapse. Such materials in hazardous quantities are considered to be "immediately" dangerous to life or health.
• Inerting. Displacing the atmosphere in a permit space by a noncombustible gas (such as nitrogen) to such an extent that the resulting atmosphere is noncombustible. Note: This procedure produces an IDLH oxygen-deficient atmosphere.
• Isolate or isolation. The process by which employees in a confined space are completely protected against the release of energy and material into the space, and contact with a physical hazard, by such means as: Blanking or blinding; misaligning or removing sections of lines, pipes, or ducts; a double block and bleed system; lockout or tagout of all sources of energy; blocking or disconnecting all mechanical linkages; or placement of barriers to eliminate the potential for employee contact with a physical hazard.
• Isolation Barriers. Physical barriers that are used to separate workers from hazards within a confined space. These barriers help prevent exposure to harmful substances or mechanical risks.

J

• Job Hazard Analysis (JHA). A systematic process used to identify and evaluate hazards associated with a specific job or task, such as confined space entry, to ensure proper safety measures are implemented.

K

• Kickout. The sudden displacement of a worker or object in a confined space due to a shift in material, such as soil or liquids, often leading to engulfment or entrapment hazards.

L

• Limited or restricted means for entry or exit. A condition that has a potential to impede an employee's movement into or out of a confined space. Such conditions include, but are not limited to, trip hazards, poor illumination, slippery floors, inclining surfaces and ladders.
• Line breaking. The intentional opening of a pipe, line, or duct that is or has been carrying flammable, corrosive, or toxic material, an inert gas, or any fluid at a volume, pressure, or temperature capable of causing injury.
• Lockout/Tagout. A safety procedure used to ensure that energy sources are completely shut off and isolated before workers enter confined spaces. Lockout/tagout procedures prevent accidental energization of equipment during maintenance or repairs.
• Lower Explosive Limit (LEL). The lowest concentration of a gas or vapor in the air that can ignite when an ignition source is introduced. Below this level, the mixture is too lean to explode.
• Lower Flammability Limit (LFL). The minimum concentration of a gas or vapor in the air that can ignite. Below this concentration, the air-fuel mixture is too lean to support combustion.

M

• Monitor or monitoring. The process used to identify and evaluate the hazards after an authorized entrant enters the space. This is a process of checking for changes that is performed in a periodic or continuous manner after the completion of the initial testing or evaluation of that space.

N

• NIOSH (National Institute for Occupational Safety and Health). A research agency focused on the study of workplace safety and health under the U.S. Centers for Disease Control and Prevention. NIOSH is responsible for conducting research and making recommendations to prevent occupational injuries and illnesses, including those associated with confined spaces. It provides resources, such as guidelines and best practices, for employers and workers.
• Non-entry rescue. Rescue that occurs when a rescue service, usually the attendant, retrieves employees in a permit space without entering the permit space.
• Non-permit confined space. A confined space meets the definition of a confined space but does not meet the requirements for a permit-required confined space. It does not pose significant hazards to workers' safety and health, and therefore does not require a permit for entry.
• Normal Oxygen Level. The standard concentration of oxygen in the air, typically around 20.9%. This level is considered safe for breathing in confined spaces.

O

• OSHA (Occupational Safety and Health Administration). A U.S. federal agency within the Department of Labor that enforces standards for workplace health and safety. OSHA regulates confined space safety through the Permit-Required Confined Spaces Standard (29 CFR 1910.146), which mandates procedures for identifying and controlling hazards in confined spaces to protect workers. Employers are required to follow OSHA guidelines for confined space entry, including permits, training, and rescue plans.
• Oxygen Deficiency. A condition in which the oxygen level in a confined space falls below 19.5%, making it dangerous for workers to breathe. Oxygen deficiency can lead to unconsciousness or death if not corrected.
• Oxygen Enrichment. A condition where the oxygen concentration in a confined space exceeds 23.5%, increasing the risk of fire or explosion. Workers must monitor oxygen levels to prevent such hazards.

P

• Permit. A written or printed document that authorizes entry into a permit-required confined space and specifies the precautions and conditions that must be met before and during entry. It ensures that all safety procedures are in place.
• Permit-required confined space. (permit space) A confined space that has one or more of the following characteristics:
1. Contains or has a potential to contain a hazardous atmosphere;
2. Contains a material that has the potential for engulfing an entrant;
3. 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
4. Contains any other recognized serious safety or health hazard.
• Permit-required confined space program. (permit space program) means the employer's overall program for controlling, and, where appropriate, for protecting employees from, permit space hazards and for regulating employee entry into permit spaces.
• Physical hazard. An existing or potential hazard that can cause death or serious physical damage. Examples include, but are not limited to: Explosives (as defined by paragraph (n) of § 1926.914, definition of "explosive"); mechanical, electrical, hydraulic and pneumatic energy; radiation; temperature extremes; engulfment; noise; and inwardly converging surfaces. Physical hazard also includes chemicals that can cause death or serious physical damage through skin or eye contact (rather than through inhalation).
• Prohibited condition. Any condition in a permit space that is not allowed by the permit during the period when entry is authorized. A hazardous atmosphere is a prohibited condition unless the employer can demonstrate that personal protective equipment (PPE) will provide effective protection for each employee in the permit space and provides the appropriate PPE to each employee.

Q

• Qualified person. One who, by possession of a recognized degree, certificate, or professional standing, or who by extensive knowledge, training, and experience, has successfully demonstrated his ability to solve or resolve problems relating to the subject matter, the work, or the project.

R

• Representative permit space. A mock-up of a confined space that has entrance openings that are similar to, and is of similar size, configuration, and accessibility to, the permit space that authorized entrants enter.
• Rescue. Retrieving, and providing medical assistance to, one or more employees who are in a permit space.
• Rescue Plan. A detailed plan that specifies the procedures and equipment needed to safely remove a worker from a confined space in the event of an emergency, such as an injury or hazardous atmosphere. The plan includes methods of communication, necessary rescue equipment (e.g., lifelines, harnesses), and designated rescue personnel who are trained to perform confined space rescues. OSHA requires a rescue plan to be in place before workers enter permit-required confined spaces.
• Rescue service. The personnel designated to rescue employees from permit spaces.
• Retrieval system. The equipment (including a retrieval line, chest or full body harness, wristlets or anklets, if appropriate, and a lifting device or anchor) used for non-entry rescue of persons from permit spaces.

S

• Safety Data Sheet (SDS). A document that provides detailed information about the hazards of chemicals, including those that may be found in confined spaces. SDSs include instructions for the safe handling, storage, and emergency procedures related to each chemical.
• Self Rescue. The ability of a worker to exit a confined space without the assistance of others, typically in response to a hazardous condition. Self-rescue plans are critical in confined space entry protocols.
• Serious physical damage. An impairment or illness in which a body part is made functionally useless or is substantially reduced in efficiency. Such impairment or illness may be permanent or temporary and includes, but is not limited to, loss of consciousness, disorientation, or other immediate and substantial reduction in mental efficiency. Injuries involving such impairment would usually require treatment by a physician or other licensed health-care professional.

T

• TagoutTagout is:
1. The placement of a tagout device on a circuit or equipment that has been deenergized, in accordance with an established procedure, to indicate that the circuit or equipment being controlled may not be operated until the tagout device is removed; and
2. The employer ensures that:
   1. Tagout provides equivalent protection to lockout; or
   2. That lockout is infeasible and the employer has relieved, disconnected, restrained and otherwise rendered safe stored (residual) energy.
• Test or testing. The process by which the hazards that may confront entrants of a permit space are identified and evaluated. Testing includes specifying the tests that are to be performed in the permit space. Note: Testing enables employers both to devise and implement adequate control measures for the protection of authorized entrants and to determine if acceptable entry conditions are present immediately prior to, and during, entry.
• Testing and Monitoring. The process of continuously assessing the atmosphere within a confined space to detect hazardous conditions, such as the presence of flammable gases or oxygen deficiency. Testing is required before entry and throughout the work period to ensure that conditions remain safe. This process is critical in identifying potential risks and preventing exposure to dangerous environments.

U

• Upper Explosive Limit (UEL). The maximum concentration of a gas or vapor in the air above which combustion cannot occur. At concentrations above the UEL, the mixture is too rich to burn.

V

• Ventilation. A method of introducing fresh air into a confined space to control hazardous atmospheres. Mechanical ventilation, such as fans or blowers, is often used to dilute or remove toxic gases, reduce flammable vapors, or replenish oxygen levels. Proper ventilation can prevent hazardous conditions from developing and is an essential safety measure for workers in confined spaces.

W

• Warning Signage. Signs placed around confined spaces to inform workers of the potential hazards and restricted entry requirements, ensuring that only authorized personnel access the area.

X

• Xenon Gas. A rare, colorless, odorless gas sometimes used in lighting and scientific applications. In confined spaces, xenon is considered an asphyxiant, as it can displace oxygen and lead to oxygen deficiency.

Y

• Yield Stress. The stress at which a material begins to deform plastically. In confined space safety, this term is relevant when considering the structural integrity of materials like walls or floors that might collapse.

Z

• Zero Mechanical State (ZMS). The state in which all potential energy (such as mechanical, hydraulic, or pneumatic) has been released from equipment in a confined space, ensuring that no movement or pressure can cause harm. This is often part of lockout/tagout procedures.