OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at https://www.osha.gov.

December 10, 1996

Mr. Michael L. Coleman
Neotronics of North America
P.O. Box 2100
Flowery Branck, GA 30542-2100

Dear Mr. Coleman:

This is in response to your request of September 16, addressed to Occupational Safety and Health Administration's (OSHA's) Deputy Regional Administrator for Region IV requesting an interpretation of 29 CFR 1910.146 concerning the recording of atmospheric test results. Your inquiry was forwarded to my office for response.

We have repeated your questions to aid other readers with the responses.


Please define OSHA's expectation with regard to maintaining written (or stored) data relative to areas to be entered and the real time, Single Time Exposure Limits (STEL), Time Weighted Averages (TWA) values of atmospheres therein?


The Permit-Required Confined Spaces (PRCS) standard, as a generic procedural standard for work activities in permit spaces, does not address terms such as STEL and TWA. These terms related to employee health monitoring addressed by other OSHA standards.

Note: Real time, for the purposes of this response, is that time during the testing process when the direct reading instrument is viewed for the value of the substance being tested.

Regarding data OSHA expects to be maintained from the PRCS standard's position:

1. Paragraph (f)(10) requires the results of initial and periodic tests required by paragraph (d)(5) be recorded on the entry permit and maintained for 1 year. OSHA has made a determination regarding sampling results obtained through testing PRCS atmospheres. It is enclosed for your information.

2. Paragraph (c)(5)(i)(C) requires that the data resulting from monitoring and inspections demonstrate that the continuous forced air ventilation is maintaining the permit space safe for entry. As a performance standard, however, there is no minimum or maximum number of data entries. The preamble (Pg. 4488) of the final rule sheds light as to the quantity of data issue. It states . . . "The data required by paragraph (c)(5)(i)(C) are essential for the employer and employees, as well as OSHA, to be able to determine whether or not the space is being maintained safe for entry with the use of ventilation alone." Thus, from a compliance position, the quantity of data being maintained must be sufficient to convince OSHA that the powered ventilation equipment and the way the fresh air is being distributed to the immediate area where the employees are or will be working is functioning properly.

The values to be recorded on the entry permit or recorded when the atmospheric concentration needs to be documented by the standard are "real time" concentrations.


Is a user required to document actual numeric values of all three atmospheres (Real Time, STEL, and TWA) at any time?


No, from a 29 CFR 1910.146 prospective, the only values to be documented (recorded) are real time values.


Does the expectation include written documents on the atmosphere in real time real value sense prior to entry as suggested in appendix B to 1910.146 - Procedures for Atmospheric Testing Item (2) Verification testing?


Yes. The standard requires that employers record initial and periodic test results on the entry permit.


If a gas detector reads only real time values (and does no calculations for averaging STEL or TWA), in what way are alarm set-points impacted?


The PRCS standard does not require alarm set-points for testing instruments.

Regarding further assistance requested, usually the answers to questions such as these (OSHA's intent and meaning of standards) can be found either on a CD-ROM titled OSHA Regulations, Documents. and Technical Information on CD-ROM available through the Government Printing Office or OSHA's Internet server in Salt Lake City (http://www.osha.gov/). Attached is information on these two sources.

If you have further questions on this response, please contact Mr. Don Kallstrom in the Office of Safety Compliance Assistance at 202 219-8031 x 109. For other questions regarding this or another OSHA standard or regulation, please continue to work directly with OSHA's Regional staff.


John B. Miles, Jr., Director
Directorate of Compliance Programs