Chapter 6: Maintaining the Ductless Enclosure
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There are five means of determining when its time to change the carbon
filters (not shown in the order of preference).
Odor -
A person’s sensitivity to odor, tolerance of odor and their comfort
level under odoriferous conditions vary with the individual. Odor is an
indicator that chemicals are passing through the carbon filter. Additionally,
several points need to be understood:
•
Odor can be used as a prompt to sample the exhaust to confirm
breakthrough.
•
Organic chemicals approved for use in the ductless hood usually have
odors that are detectable before reaching the time weighted exposure
limits.
Safety-First Vapor Sensor -
The organic sensor detects filter saturation
from exhaust gas concentration to alert the operator to replace filters. The
electronic sensor will signal when the concentration is under 5 ppm for most
chemicals with a range of 0.1-30 ppm. The early warning provided by the
Safety-First Vapor Sensor provides the user ample time (5-10% remaining
filter life) to complete work in process before replacing the filters. The vapor
sensor includes a primary and backup sensor for redundant monitoring and
both sensors detect typical organic solvents, smoke particulates, ammonia
gases, formaldehyde gases, and hydrogen sulfide gases; the vapor sensor does
not detect mineral acid gases such as hydrochloric acid, nitric acid, or sulfuric
acid. Consult the table in
Chapter 4
for a partial listing of tested chemicals in
order of sensitivity as the sensitivity differs for each chemical; most tested
chemicals have a sensitivity alert concentration below 5 ppm as provided in
the table in
Chapter 4
.
Detection Tubes -
Color change indicators can be used to measure the
concentration of the chemical at the exit side of the carbon filter, between
filters, or in the outlet exhaust. A kit including syringe pump and flexible
tubing can be purchased as an accessory from Labconco (Catalog #
6924900). Labconco Customer Service Representatives are supplied with
detector tube catalog numbers, as well as telephone numbers to direct you to
where to purchase these items.
For organic, mineral acid, formaldehyde and ammonia, chemical specific
detector tubes should be purchased when installing fresh filters. Each kit
contains instructions on how many strokes of the syringe are required to
obtain the stated sensitivity. The sampling syringe is connected to the
ductless enclosure exhaust. The hose from the sampling syringe inlet can be
Safety Note:
The use of the organic sensor is
not recommended
for the
determination of filter saturation when the exposure limit/TWA for the
chemical is under 5 ppm. Other detection methods
must
be implemented
unless
testing is performed by the end user and the known exhaust
concentration is below the acceptable exposure limit/TWA.
