Safety Tidbit 2.35 – Is a spray booth necessary?
Reference: OSHA
Letter of Interpretation July 14, 2009
A colleague recently asked me when is a booth necessary for
spray painting operations? His example was that the employer periodically spray
applies flammable paints (not aerosol cans) on signs and the back of large
construction trucks. The operation lasts less than 15-20 minutes and uses a
quart or less of paint at a time.
OSHA’s
1910.94(c)(2) states that spray booths or spray rooms are to be used to enclose
or confine all spray finishing using organic or inorganic materials. Since the
primary purpose of 1910.94(c) is to protect health, this is not a big deal if
the appropriate PEL in Subpart Z of Part 1910 is not exceeded.
Therefore,
if no OSHA PEL is exceeded during spray finishing operations, the operation
falls under the OSHA standard at 1910.107. That standard does not have an
enclosure provision like 1910.94(c) requiring that all spray finishing using flammable and combustible materials be
confined to spray booths or spray rooms. However, the 1910.107(g)(1) requires
that "[spraying shall not be conducted outside of predetermined spraying
areas." Paragraph 1910.107(a)(2) defines a "spraying area" as
"[any area in which dangerous quantities of flammable vapors or mists, or
combustible residues, dusts, or deposits are present due to the operation of
spraying processes." OSHA interprets "dangerous quantities of
flammable vapors or mists" in 1910.107(a)(2), to be areas with
concentrations exceeding 25% of the lower flammable limit (LFL) of any chemical
used at any time during the spray finishing operations, without the benefit of
ventilation required under the standard.
Example: To
determine the lower explosive limits of the most common solvents used in spray
finishing, see Table G-11 of 1910.94. Column 1 gives the number of cubic feet
of vapor per gallon of solvent and column 2 gives the lower explosive limit
(LEL) in percentage by volume of air. Note that the quantity of solvent will be
diminished by the quantity of solids and nonflammables contained in the finish.
To determine the volume of air in cubic feet necessary to
dilute the vapor from 1 gallon of solvent to 25 percent of the lower explosive
limit, apply the following formula:
Dilution volume required per gallon of solvent =
4 X (100 - LEL) X (cubic feet of vapor per gallon) / LEL
Using toluene as the solvent.
1. LEL of toluene from Table G-11, column 2, is 1.4 percent.
2. Cubic feet of vapor per gallon from Table G-11, column 1,
is 30.4 cubic feet per gallon.
3. Dilution volume required =
4 X (100 - 1.4) X 30.4 / 1.4
= 8,564 cubic feet/gallon.
4. To convert to cubic feet per minute of required ventilation,
multiply the dilution volume required per gallon of solvent by the number of
gallons of solvent evaporated per minute.
Therefore: If the operation uses one quart of paint over 15
minutes.
(0.25 gallons/15 minutes) = 0.0167gallons/minute
or GPM
or in other words, one gallon will
evaporate every approx. 60 minutes
5. 8,564 CF/gal X 0.0167 GPM = 143 CFM
However, 25 percent of the LEL or in our example above 1.4%/25
equals 0.056%. Converted to parts per million (PPM) is 0.056%X10,000=560 PPM. OSHA’s
acceptable ceiling concentration for Toluene is 300 PPM and OSHA’s acceptable maximum peak above
the acceptable ceiling concentration for an 8-hr shift is 500 PPM. All provided
the total 8-hour time-weighted average stays below 200 PPM.
So
back to the original question of whether a spray booth was necessary. More
information is needed (SDS) and an industrial hygiene evaluation of the work
area.
Hope this was helpful and thanks for reading my Safety
Tidbits ~ Bryan
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