Scenario: When installing spray foam insulation in a commercial building you are using multiple negative air machines to control worker exposures to methylene bisphenyl isocyanate (MDI). Your letter summarized how you evaluated the respiratory hazards in the work area, and you require your installers to wear full face air purifying respirators in the work area. Your evaluation was based on a copy of the manufacturer's material safety data sheet (MSDS) for the foam insulation, as well as a re-occupancy guideline from a manufacturer of foam insulation.
Question: To comply with §1910.134(d)(l)(iii) of OSHA's Respiratory Protection standard, would it be necessary to conduct air
testing to evaluate respiratory hazards from the MDI during the
application of the foam since the workers are already being required to
wear full-face air-purifying respirators?
Response: Not necessarily. OSHA's Respiratory
Protection standard at §1910.134(d)(l)(iii) states, "The employer shall
identify and evaluate the respiratory hazard(s) in the workplace; this
evaluation shall include a reasonable estimate of employee exposures to
respiratory hazard(s) and an identification of the contaminant's
chemical state and physical form." Although the most reliable and
accurate method to determine exposure is to conduct personal air
monitoring, it is not explicitly required by the Respiratory Protection
standard. Instead, other means can be used to estimate workplace
exposures. These methods include, but are not limited to, the use of
objective data, application of mathematical approaches, and others.
Additional information regarding hazard evaluation can be found at CPL 02-00-120, Inspection Procedures for the Respiratory Protection Standard,
paragraph E. When using any of these methods, the data needs to be
accurate and representative of conditions at the current work site,
including materials being applied and work being performed. In addition,
the assessment would also need to consider exposures to any other
hazardous chemicals in the foam-application process.
The re-occupancy study that you provided should not be considered a
representative estimate of your workers' exposures to MDI during the
application of spray foam insulation. The study was a proposed method
for determining the delay required before safely reoccupying a building
following application of spray-foam insulation. The study did not
provide any exposure data for workers' exposures to MDI or other
chemicals during application of spray-foam insulation. Thus, this data
would not satisfy the requirement at 1910.134(d)(l)(iii) for selection
of appropriate respiratory protection.
In conclusion, a reasonable estimate of employee exposure would need to
include data that closely resembles your work operation and expected
chemical exposures. As stated above, the most accurate and reliable data
is obtained by conducting personal air monitoring of your actual
You should be aware that 27 states, including Connecticut, administer
their own OSHA-approved occupational safety and health programs, or
State Plans. All State Plans are required to cover public sector (state
and local government) employees (29 U.S.C. 667(c)(6)), and 22 State
Plans also cover the private sector. These State Plans must adopt and
enforce standards that are at least as effective as those standards
promulgated by Federal OSHA (29 U.S.C. 667(c)(2)).