OSHA defines a confined space as one that is large enough to enter and perform assigned work in, but has limited or restricted ways to enter or exit and is not designed to be occupied continuously by a worker. A permit space is a confined space that has any serious safety or health hazards such as containing a hazardous atmosphere; containing a material than can engulf a person; or one that has an inside design that could trap or asphyxiate a person who is inside. Any one of these hazards or a combination of these or any hazards to health or safety in a confined space requires a permit to be issued in order to enter and work in the confined space.
Atmospheric testing is required to evaluate the hazards of a permit space and to verify that acceptable conditions exist to allow entry into that space. To test the atmosphere in a confined space, equipment that can detect chemicals at levels well below the defined exposure limits is used. In this way it can be determined what chemical hazards may be present (or become present) in the space’s atmosphere. Once hazardous chemicals are identified, it can be determined what steps will be necessary to ensure that the atmosphere is safe for a worker to enter. Testing results are evaluated or reviewed by a technically qualified professional such as a certified industrial hygienist, a registered safety engineer, or a certified safety professional from an OSHA consultation service.
Before workers can enter a permit space, the same atmospheric testing must be done again to make sure that the chemical hazards that may be present are within safe levels, as identified on the permit. Tests are done for oxygen levels, for combustible gases, and for toxic gases and vapors. These test results are also recorded on the permit. There is a minimum response time for the testing device to detect the chemicals set by the manufacturer of the equipment, but if hosing or a probe extension is attached for spaces with different depths, additional time is needed to test thoroughly.
If the permit space is deep or extends a distance beyond the entry point, there must be further atmospheric testing four feet from the entry point in the direction of travel and four feet to each side. The person doing the testing must move slowly enough to allow the equipment time to properly respond in each area before moving to a new area. Each time a space is entered or re-entered this testing must be repeated to make sure the atmospheric conditions are safe for entry.
These requirements are covered by Title 29 Code of Federal Regulations1910.146, Appendix B.