Labconco XPert Weigh Boxes 5220331 - Manual (Page 28)

Chapter 5: Using Your Glove Box
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Definition of Terms
NIOSH – National Institute for Occupational Safety and Health/Mine Safety
and Health Administration. (U.S.A.)
TWA – Recommended Exposure Limits expressed as a Time Weighted
Average. The exposure limit for that chemical for up to a 10-hour workday,
40 hours a week. Expressed in units of parts per million or milligrams per
cubic meter.
Odor Threshold – The value in parts per million or milligrams per cubic
meter for which one might expect to smell a chemical’s presence in the air.
This value is very subjective and detection will vary with the sensitivity of
one’s nose. The period of time until the odor threshold is reached in the
exhaust stream can be estimated from Labconco exclusive computerized filter
modeling program. Contact Labconco on carbon filter life for specific
applications. See Chapter 6.
Saturation Level or Time – There is a limit to the amount of chemical that
can be adsorbed by activated carbon, or neutralized by chemically-treated
carbon. Once the capacity of the carbon is reached, it is considered to be
saturated and will adsorb (or neutralize) no further material; the outlet
concentration of the chemical will equal the inlet concentration from that
point until the filter is replaced. (Note that the capacity of activated carbon is
not a constant, but varies with the inlet concentration). Labconco Technical
Specialists can determine with the computerized carbon-modeling program
the estimated time saturation for a particular chemical. When using a HEPA
filter in all filtered glove boxes or in combination with a carbon filter, the
speed control will need to be increased to allow for HEPA filter loading.
IDLH (Immediately Dangerous to Life and Health). An atmosphere that
poses an immediate hazard to life or produces immediate irreversible health
effects. IDLH concentrations should not be approached in the glove box.
Appropriate Chemicals for Carbon Filters
Below is a general set of rules to determine appropriateness of chemical
usage.
Selected organic chemicals considered to be occupational
carcinogens by NIOSH can be used in the filtered glove
box with carbon filters under rigid restrictions. See
separate discussion on carcinogens for special instructions.
Organics must have time weighted exposure limits (TWA) of 1 PPM or
greater.
Chemicals must have a detectable odor at concentrations below the TWA for
the chemical.
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