Since both the Occupational Safety and Health Administration and the Environmental Protection Agency promulgate various regulations pertaining to allowable concentrations of toxic substances in the air, the question posted here certainly seems reasonable. Indeed, OSHA does publish its table of Permissible Exposure Limits. Likewise, EPA—under the Clean Air Act—requires EPA to set National Ambient Air Quality Standards.
As to OSHA, the agency “does not test, approve, certify, or endorse any equipment, product, or procedure, including machine design and risk assessment techniques.” [Refer to fourth paragraph of linked letter] Now, there are certain products for which OSHA does require an “NRTL Approval” (nationally recognized testing lab). However, gas detection instruments are not on the list of such products.
EPA does have a program establishing designated reference and equivalent air monitoring methods for criteria air pollutants. Notably, the list of criteria air pollutants represents but a tiny fraction of the substances detailed in the OSHA table. Moreover, EPA’s mandate under the Clean Air Act covers ambient air quality, and not the workplace domain of OSHA.
Thus, no gas detection instrument approval exists in OSHA. In the case of EPA, and applicable within the realm of ambient air monitoring—as applied only to those few criteria air pollutants—there does exist a list of designated reference and equivalent methods. The products listed therein do meet EPA guidelines, and, as such, are “approved” by the agency.