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enters (inwardly converging walls, or a floorthat slopes downward to a smaller section);or i t has any other serious safety or healthhazards.

Verificat ion TestingBefore a permit space that may have a haz-ardous atmosphere can be entered, theatmosphere must be tested using the stepsidentified on the permi t (developed duringevaluation testing). Verification testing isdone to m ake sure that the chemical hazardsthat may be present are below the levelsnecessary for safe entry, and that they meetthe conditions identified on the permit . Testthe atmosphere in the following order: (1) foroxygen, (2) for combustible gases, and then(3) for toxic gases and vapors.2 The testingresults -- the actual test concentrations --must be recorded on the permit near the lev-els identified for safe entry.

Durat ion of Testing

For each test required on the permit, youmust allow enough tim e for the air from thespace to be drawn into the equipment andfor the sensor (or other detection device) toreact to the chemical if it is present. This is

considered the min imum response timeand it w ill be noted by the m anufacturer inthe operator s manual. Be aware that youwil l need to add time to this "min imumresponse time" if you have attached hosingor a probe extension to the inlet. The addi-tional time is needed to allow the air fromthe different depths of the space to be pul ledinto the equipment inlet.

A confined space is one that is largeenough to enter and perform assigned workin; it has limi ted or restricted ways to enteror exit the space; and i t was not designed tobe occupied continuously by a w orker.

Evaluation testingThe atmosphere with in a confined spacemust be tested using equipment that isdesigned to detect the chemicals that m aybe present at levels that are well below thedefined exposure lim its. Evaluation testingis done to: determine what chemical hazards are or

may become present in the spaces atmos-phere, and

identify what steps must be follow ed andwhat conditions must be met to ensurethat atmospheric condi tions are safe for aworker to enter the space.

The testing results and the decisions aboutwhat steps must be followed before entrymust be evaluated by, or reviewed by, atechnically qualified professional like anOSHA consultation service, a certifiedindustrial hygienist, a registered safetyengineer, or a certified safety professional.

The technically qualified professional m ustconsider all of the serious hazards in his/herevaluation or review.

A permi t space is a confined space that hasone or more of the following features: it hasor m ay contain a hazardous atmosphere; itcontains a material that can engulf a personwho enters; it has an inside design thatcould trap or asphyxiate a person who

FactSheetProcedures for Atmospheric Testing

in Confined Spaces1Atmospheric testing is required for two distinct purposes: evaluation of the

hazards of the permit space and verification that acceptable conditions exist for

entry into t hat space.

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Testing Conditions in Spaces that MayHave Layered At mospheresFor permit spaces that are deep or haveareas leading away from the entry point, theatmosphere may be layered or may be differ-ent in remote areas. For these spaces, test-ing must be done in the area surrounding

the worker, which is considered four (4) feetin the direction of travel and to each side. Ifa sample probe is used to do the testing,

This is one in a series of informat ional fact sheets highlighting OSHA programs, policies or

standards. It does not impose any new compliance requirements. For a comprehensive list of

compliance requirements of OSHA standards or regulations, refer to Title 29 of the Code of Federal

Regulations. This information will be made available to sensory impaired individuals upon request.The voice phone is (202) 693-1999; teletypewriter (TTY) number: (877) 889-5627.

then the worker must move slowly enoughso that testing is completed, keeping theequipment response time in mind, beforehe/she moves into the new area.

Retesting the Space During Entry orBefore Re-Entry

Test the permi t space rout inely to m ake surethat the atmospheric conditions continue tobe safe for entry.3

U.S. Department of Labor

www.osha.gov(800) 321-OSHA

For more complete information:

DSTM 9/2005

1 Title 29 Code of Federal Regulations 1910.146, Appendix B.2 29 CFR 1910.146(c)(5)(ii)(C) and (d)(5)(iii).3 29 CFR 1910.146(c)(5)(ii)(F) and (d)(5)(ii).