If you aren’t confident in your knowledge of one of the following subjects, go back to the relevant lesson in the course to give it a review.

• Meters for testing LEL levels read in percentages of the LEL.
• PEL stand for – Permissible Exposure Limits.
• Short Term Exposure Limit (STEL) is usually 15 minute time weighted average.
• The Acronym TWA stand for Total Weight Atmospheric.
• NIOSH Recommend A time-weighted average concentration for up to a 10-hour workday during a 40-hour workweek.
• In summary IDLH means You have 30 minutes to get out without irreversible adverse health affects. 
• TLV is a reserved term of the American Conference of Governmental Industrial Hygienists.
• LEL Gas Monitors can’t detect benzene, toluene, diesel and hexane.
• Most meters are calibrated to measure oxygen concentrations between: 0 and 25 percent by volume in air.
• The atmosphere within a confined space must be tested using equipment that is designed to detect the chemicals that may be present at levels that are well below the defined exposure limits
• Verification for atmosphere in the following order – Oxygen, combustible gases, toxic gases and vapors
• Layered Atmosphere Testing must be done in the area surrounding the worker, which is considered four (4) feet in the direction of travel and to each side, then the worker must move slowly enough so that testing is completed, keeping the equipment “response time” in mind, before he/she moves into the new area.
• Most atmospheric hazards in a confined space are invisible to the naked eye as well as odorless.
• Vapors with a high density are more dangerous and require better ventilation because they tend to flow along the floor and collect in low spots.
• Gases have three characteristic properties – They are easy to compress, they expand, they occupy more space than liquids or solids
• Oxygen (O2) levels need to stay between 19.5% and 22% in confined spaces!