- Standard Number:
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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
Oakville, Ontario
Canada L6L2X8
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