(a) (1) Exposures by inhalation, ingestion, skin absorption, or
contact to any material or substance (i) at a concentration above those
specified in the ``Threshold Limit Values of Airborne Contaminants for
1968'' of the American Conference of Governmental Industrial Hygienists,
except for the ANSI Standards listed in Table I of this section and
except for the values of mineral dusts listed in Table II of this
section, and (ii) concentrations above those specified in Tables I and
II of this section, shall be avoided, or protective equipment shall be
provided and used.
(2) The requirements of this section do not apply to exposures to
airborne asbestos dust. Exposures of employees to airborne asbestos dust
shall be subject to the requirements of 29 CFR 1910.93a.
(b) To achieve compliance with paragraph (a) of this section,
feasible administrative or engineering controls must first be determined
and implemented in all cases. In cases where protective equipment in
addition to other measures is used as the method of protecting the
employee, such protection must be approved for each specific application
by a competent industrial hygienist or other technically qualified
source.
Table II-- Mineral Dusts
------------------------------------------------------------------------
Substance Mppcfe Mg/M \3\
------------------------------------------------------------------------
Silica:
Crystalline:
Quartz (respirable)....................... 250f 10mg/M
\3\m
-------------------------
%SiO2+5 %SiO2+2
Quartz (total dust)....................... ........... 30mg/M \3\
------------
%SiO2+2
Cristobalite: Use \1/2\ the value calculated
from the count or mass formulae for quartz.
Tridymite: Use \1/2\ the value calculated
from the formulae for quartz.
Amorphous, including natural diatomaceous
earth...................................... 20 80mg/M \3\
------------
%SiO2
============
Silicates (less than 1% crystalline silica):
Mica...................................... 20
Soapstone................................. 20
Talc...................................... 20
Portland cement........................... 50
Graphite (natural).......................... 15
Coat dust (respirable fraction less than 5%
SiO2)...................................... ........... 2.4mg/M
\3\
or
For more than 5% SiO2....................... ........... 10mg/M \3\
------------
%SiO2+2
Inert or Nuisance Dust:
Respirable fraction....................... 1 5mg/M \3\
Total dust................................ 505 15mg/M3
------------------------------------------------------------------------
Note: Conversion factors--
mppcf x 35.3=million particles per cubic meter
=particles per c.c.
eMillions of particles per cubic foot of air, based on impinger samples
counted by light-field technics.
fThe percentage of crystalline silica in the formula is the amount
determined from air-borne samples, except in those instances in which
other methods have been shown to be applicable.
jAs determined by the membrane filter method at 430 x phase contrast
magnification.
mBoth concentration and percent quartz for the application of this limit
are to be determined from the fraction passing a size-selector with
the following characteristics:
------------------------------------------------------------------------
Percent
Aerodynamic diameter (unit density sphere) passing
selector
------------------------------------------------------------------------
2 90
2.5 75
3.5 50
5.0 25
10 0
------------------------------------------------------------------------
The measurements under this note refer to the use of an AEC instrument.
If the respirable fraction of coal dust is determined with a MRE the
figure corresponding to that of 2.4 Mg/M \3\ in the table for coal
dust is 4.5 Mg/M \3\
[36 FR 23217, Dec. 7, 1971]
