- Standard Number:
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.
September 4, 1996
Mr. Macon Jones
Blasting Cleaning Products LTD.
2180 Speers Road
Dear Mr. Jones:
This is response to your request of April 10, requesting clarification of the 29 CFR 1910.146 standard. Please accept our apology for the delay. Responses to your questions follow:
Question 1. If an enclosed space is a "permit required confined space" (PRCS) and all of the proper procedures are implemented, can entry be made and work performed (or continued) if the measured lower flammable limit (LFL) is greater than 10%? Answer Yes. The permit-required confined spaces standard (29 CFR 1910.146) does not prohibit working in a permit-required space where the atmosphere is above 10% of the LFL. Once the atmosphere is above 10% of the LFL, all of the requirements of the standard must be met. Question 2. Regarding the above question (question 1) are there particular procedures or precautions that are required under these conditions? Answer Since PRCS is a performance standard, it does not specify procedures for conditions where the permit-required space has a hazardous flammable atmosphere. However, what the standard does specify in paragraph (d) is that the employer must identify and evaluate each hazard to which the entering employees will be exposed. Based on the hazard analysis, the employer must develop and implement the means, procedures, and practices necessary for safe permit space entry operations. Although the PRCS standard may not specify or necessarily apply to specific precautions an employer must take regarding a hazardous flammable atmosphere, other OSHA standards could apply. For example, if the flammable atmosphere also presented a respiratory hazard requiring protection, 29 CFR 1910.134 specifies precautions relative to the selection and use of respirators. If the flammable atmosphere is the result of a process involving equipment, there may be precautions with regard to the equipment that an employer would be required to follow. Question 3. Have OSHA or any other government agencies made specific studies regarding the difficulties of accurately calibrating (LFL) monitoring devices, when multiple solvent coatings are used in a spray coating? Answer OSHA is not aware of any specific studies that have been conducted in this area. However, we understand that most manufacturers of this type of testing equipment have addressed this issue. Manufacturers setup and calibrate their equipment using a single calibration gas (usually menthane) and then provide their end users with conversion tables or factors for determining the percentage of the LFL for other gases. Where the finish being applied is a mixture, the manufacturer of the coating, through the Material Safety Data Sheet or other product information, is able to advise the employer of the individual solvent characteristics. Question 4. Have OSHA or any other government agencies made specific studies as to minimum and maximum distances LFL monitoring equipment may be located from the spray process, without adversely affecting worker safety? (Or adversely affecting monitoring equipment reliability?) Where can copies of these study results be obtained? Per your conversation with Don Kallstrom of my staff, the root question is, Where and how often is monitoring required under 29 CFR 1910.146(d)(5)(ii) to meet the intent of the standard for a spray painting operation within a railroad tank car? Answer The standard does not specify frequency rates because of the performance oriented nature of the standard and the unique hazards of each space. However, there will always be, to some degree, testing or monitoring during the entry operations which is reflective of the atmospheric hazard. The employer must determine the degree and the frequency of testing or monitoring. Some of the factors that affect frequency are results of test allowing entry, the regularity of entry (daily, weekly, or monthly), the uniformity of the permit space (the extent to which the configuration, use, and contents vary), the documented history of previous monitoring activities, and knowledge of the hazards which affect the permit space as well as the historical experience gained from monitoring results of previous entries. Knowledge and recorded data gained from successive entries (such as ventilation required to maintain acceptable entry conditions) may also be used to document changes in the frequency of monitoring. The placement of the testing or monitoring instrument in relation to the employee performing spray coating operations is also not specified in the standard. The intent of this paragraph is to ensure that the predetermined acceptable entry conditions established by the employer are being maintained during the entry. Where the employer can demonstrate that the hazard concentration to which the employee is being exposed is uniform throughout the tank car being sprayed, then the placement of the instrument is not critical.
Should you have further questions on this correspondence please contact Mr. Don Kallstrom of my Office of Safety Compliance Assistance staff (202)219-8031 x 109.
John B. Miles, Jr., Director
Directorate of Compliance Programs