Osha Glossary Of Confined Space Terms And Definitions

Manufacturers of gas monitors, are frequently asked to help describe certain terms used for confined space monitoring. As a manufacturer of both oxygen monitors and carbon dioxide monitors, customers often require guidance on a variety of topics focused on confined space monitoring of both oxygen and carbon dioxide.

The following are several common terms dealing with confined space along with their definitions. The terms were obtained at the OSHA web site. More detailed information, including additional terms, can be found at http://www.osha.gov

• Acute: Acute effects appear shortly after exposure, usually one to three days, while chronic effects take longer to appear, sometimes months or years.
  
  

• Air changes per hour: Air changes per hour means the number of times that the volume of a space (ft3) is moved through the space by a fan or mechanical mover.
  
  
• Broad range sensors: Broad range sensors are sensors that only indicate that a hazardous threshold of a class of chemicals has been reached.
  
  
• Chemical asphyxiants: Chemical asphyxiants are a special category of toxin. They render the body incapable of using an adequate supply of oxygen.
  
  
• Confined Space: Confined space means a space that:

(1)   Is large enough and so configured that an employee can bodily enter and perform assigned work; and

(2)   Has limited or restricted means for entry or exit (for example, tanks, vaults, and pits are spaces that may have limited means of entry.); and

(3)   Is not designed for continuous employee occupancy.

• Confined Space Entry: Confined space entry means the action by which a person passes through an opening into a permit-required confined space. Entry includes ensuing work activities in that space and is considered to have occurred as soon as any part of the entrant’s body breaks the plane of an opening into the space.
  
• Eight-hour time weighted average: The eight-hour time weighted average (TWA) refers to concentrations of airborne toxic materials that have been averaged over an eight-hour working day.
  
• Hazardous atmosphere: Hazardous atmosphere means 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% of its lower flammable limit (LFL);

(2)   Airborne combustible dust at a concentration that meets or exceeds LFL; (Note: This concentration may be approximated as a condition in which the dust obscures vision at a distance of five feet or less.

(3)   Atmospheric oxygen concentration below 19.5% or above 23.5% (Note: Ambient Air Oxygen Monitors and Oxygen Analyzers frequently have provisions for setting lower and higher oxygen alarm limits.)

(4)   Atmospheric concentration of any substance for which a dose or a permissible exposure limit is published in Subpart G, Occupational Health and Environmental Control, or in Subpart Z, Toxic and Hazardous Substances, of this part 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 provision

(5)   Another atmospheric condition that is immediately dangerous to life or health. 

• IDLH: Immediately dangerous to the life or health (IDLH) means any condition that poses an immediate or delayed threat to life or that would cause irreversible adverse health effects or that would interfere with an individual’s ability to escape unaided from a permit space.
  
  
• LEL: The lower explosive limit, LEL, is the minimum concentration of vapor or gas in air below which propagation of flame does not occur on contact with a source of ignition. Below the LEL, there is too little combustible fuel to sustain a flammable mixture.
  
  
• LFL: The lower flammable limit, LFL, is the minimum concentration of vapor or gas in air below which propagation of flame does not occur on contact with a source of ignition. Below the LFL there is too little combustible fuel to sustain a flammable mixture.
  
  
• Primary Calibration: Primary calibration means testing an instrument for accuracy and sensitivity throughout the complete range specified by the manufacturer. Federal compliance officers send gas detection equipment to the OSHA Cincinnati Technical Center for calibration at a minimum of every two years.
  
  
• Upper Explosive limit: Upper explosive limit (UEL) is the maximum concentration of vapor or gas in air above which propagation of flame does not occur or contact with a source of ignition. Above the UEL there is too little oxygen to sustain a flammable mixture.
  
  
• Ventilation: Ventilation is a method of controlling the environment with airflow.