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.

October 9, 1985

               Area Director, Baltimore


FROM:          LINDA R. ANKU
               Regional Administrator

SUBJECT:       Interpretation of 29 CFR 1910.430(b)(4)

This is in response to your written inquiry of September 17, 1985 (copy attached) which requested interpretation of 1910.430(b)(4) which states that the output of air compressor systems shall be tested for air purity every 6 months by means of oil samples taken at the connection to the distribution system. The exception is that non-oil lubricated compressors need not be tested for oil mist.

Some employers and other compressor users feel that testing for air purity is not necessary when air is properly filtered at the intake and the compressor uses a non-hydrocarbon lubricating oil. Perusing the attached reports from Texas Research Institute, it is apparent that a filter at the compressor inlet does an adequate job of establishing air quality to acceptable standards. However, there is no uniform filter maintenance schedule that is followed by all compressed air suppliers and there is no standard for distance away from the compressor to areas containing exhaust and other contaminants. Also, a substantial percentage of air compressors are driven by gasoline engines exposing the air to internal combustion engine contaminants.

Even when the compressor uses Monolec oil, satisfactory air quality cannot be obtained when the filters are not maintained properly. (See attached letter dated August 20, 1985 from Lubrication Engineers, Inc. to McLean Contracting Company. The Lebanon, PA Fire Station No. 1 changes the filters in its air purifier after 40 hours of use. (See attached article dated November 1975.)

In view of the above, it is our interpretation that 29 CFR 1910.430(b)(4) cannot be relaxed and the standard shall be cited when compressor systems have not been tested for air purity at 6-month intervals.


September 17, 1985

               ARA/Tech Support

               Area Director

               Safety & Occupational Health Specialist

SUBJECT:       Interpretation of 1910.430(b)(4)

At a recent informal conference, the violation of not testing the output of air compressor systems for air purity every six months was discussed.

The argument was made that the air compressor's source of intake is filtered and all contaminants removed from the ambient air before entering the compressor, and the compressor is located away from areas containing exhaust or other contaminants. In addition, the compressors are lubricated with monolec oil, a non-hydrocarbon lubricant, eliminating the possibility of oil mist, CO or CO2 buildup.

NOAA, diving physicians, compressor users and manufacturers, and lubricant engineers are all in apparent agreement that there is no need for testing the air when it is properly filtered at the intake and the compressor uses a non-hydrocarbon oil lubricant.

The question arise: Should we cite this standard when these conditions are met?

August 20, 1985

Mr. George Mitchell
McLean Contracting Company
2001 Benhill Avenue
Baltimore, MD 21226

Dear Mr. Mitchell:

As we discussed in our phone conversation on August 19, 1985, attached are copies of our air quality approvals for Monolec Air Compressor Oil. As you can see, in 1976 our oil was tested by the Texas Research Institute under the National Divers' Air Quality Assurance Program. This testing confirmed that our product met all specifications for breathing air as recommended in the U.S. Navy Diving Manual and by the Compressed Gas Association for grades up to Grade F.

There have been no significant changes in our Monolec Air Compressor Oil since 1976 that would adversely affect this approval or the air quality. An important ingredient to air quality is the proper maintenance of the necessary filters and traps.

I hope that the attached information meets your needs. If you require additional information, please do not hesitate to contact me.


Technical Services Engineer
Lubrication Engineers, Inc.

April 1, 1976

Lubrication Engineers, Inc.
c/o H. Lee Buras
102 Bolton Street
Gretna, Louisiana 70053

Dear Lee:

Enclosed are two separate copies of the air analysis that was recently taken on various Quincy Air Compressors used for furnishing air to our divers for breathing purposes.

The air from some of these compressors was analyzed by the Texas Research Institute, Inc., 6500 Trapor Lane, Austin, Texas 78721 under the National Divers Air Quality Assurance Program and the other group was analyzed by Mr. Marvin Welsh, 745 Holyoke Place, Gretna, La. 70053, a private chemical analyst.

We also are pleased to inform you that the oil used in the base of these compressors when these tests were performed was Lubrication Engineers Monolec Air Compressor Oil Number 6203-30 wt.

We now have all of our air compressors filled with your Monolec Air Compressor Oil Number 6203 and are very pleased with the performance of our equipment as well as the test results we have received.

Thank you very much for suggesting to us several years ago that we switch over to your Monolec Air Compressor oil.

Sincerely yours,

Thomas M. Angel



Fire department has own system to recharge emergency air tanks


The Occupational Safety & Health Act of 1970 (OSHA) has placed even greater emphasis on the purity of compressed air for breathing. The code specifies that "compressed air, compressed oxygen, liquid air, and liquid oxygen used for respiration shall be of high purity.... Breathing air shall meet at least the requirements of the specifications for Grade D breathing air as described in Compressed Gas Association Commodity Specification G7.1-1966." The code further restricts the method of producing compressed air for breathing: "If an oil- lubricated compressor is used, it shall have a high-temperature or carbon monoxide alarm, or both. If only a high-temperature alarm is used, the air from the compressor shall be frequently tested for carbon monoxide to insure that it meets the specifications."