You Have Safety Questions? We Have Safety
Answers!
««« By the STAO Safety Committee
The STAO Safety Committee welcomes enquiries, with respect to safety issues,
from STAO members. Please send your questions to the Safety Committee Chair
(refer to page 4 ‘Committee Chairs’). Your questions and the
STAO Safety Committee responses may be published in Crucible, particularly
if the information is deemed of general interest to other STAO members.
Anonymity, however, will be guaranteed.
Question 26
Our Board is looking to replace/upgrade some of the fume hoods in some
of our secondary science classrooms, in response to the use and disposal
of flammable liquids. I was wondering if there are any overarching principles
to guide us when planning to purchase standalone fume hoods? While instal¬lation
is not a problem, the school automatically says they need one, and we
are trying to keep costs reasonable. Do you know of any considerations,
suppliers or materials that we should be examining, that would not be
too onerous to share? If so, that would be most appreciated. Thank you
for any assistance you may be able to provide.
Response
While the STAO Safety Committee cannot endorse or recommend specific
designs or manufacturers of this equipment, we can provide some general
principles to aid you in your selection.
The STAO Safety Committee recommends that fume hoods be installed whenever
there is a potential that science class activities will generate unacceptable
levels of toxic fumes or otherwise objectionable airborne materials (Stay
Safe!, p. 10).
There is a discussion of hazardous chemicals that might require use
of a fume hood on p. 39 of this publication, which is available from
the STAO e-Store (www.stao.ca).
Our publication, STAO Science Laboratory Facilities Design Guide (1999)
also provides guidance on the selection of fume hoods. It is also available
from the STAO e-Store. The general principles are:
•
All chemistry and general-purpose laboratories should be equipped with
a fume hood. Labs designated for physics and non-chemistry classes
that are subject to changes in use due to programme needs, may require
fume hoods in order to allow for flexible assignment of the space.
•
The fume hood should be located away from high volume foot traffic.
•
Services installed in the fume hood should include: double gas outlet,
double electrical outlet, tap and catch pot. At least one fume hood
in the science department should have a reasonably sized sink to facilitate
safe dilution of toxic and corrosive chemicals. Also, there should
be built-in sealed light fixtures unless the fume hood is well illuminated
by daylight and the existing room lights.
•
The fume hood should have protective glazing of 6 mm thickness made
of toughened glass, laminated glass, or polycarbonate. (Note that polycarbonate
is dissolved by acetone!)
•
The sash should be moveable, and there should be a ventilation bypass
to ensure that the minimum air velocity through the opening is maintained
as the sash is lowered.
•
Venting must be to the exterior of the building and away from any ventilation
intakes.
•
The less expensive axial flow fans that are installed directly above
the fume hood are very noisy, and may interfere with teaching if left
turned on. Remote centrifugal fans are quieter and more efficient,
but more expensive.
•
A fume hood that is used for demonstrations should be an island installation
with protective glazing and size that allows a group of students to
gather around it.
Question #27
Does the STAO Safety Committee know of any legislation or have any
recommendations pertaining to the care and use of fume hoods, including
how often they should be checked?
Response
There is no provincial health and safety legislation with respect to
the use and maintenance of fume hoods. However, it might be prudent
to adopt the regulations existing in other countries (e.g., UK) which
require fume hoods to be tested at least once every 12 months. This
would mean a visual inspection, testing of the air flow and, for recirculatory
fume hoods, testing the efficiency of the filters. A record could be
kept of this regular monitoring.
Fume hoods should be kept clean and free from apparatus and bottles
not immediately required. Fume hoods should be properly maintained
and particular attention paid to the sash mechanism and the service
controls. The air flow should be checked periodically since ducts have
been known to become blocked with bird’s nests, etc. Between
the 12 month tests,
A Typical Fume Hood
a thin strip of flimsy plastic attached to the underside of the sash
will at least indicate that there is air flowing and that it is going
in the right direction.
When in use, the fan should be left running until any reaction has
ceased and the fume-hood duct is free of fumes. Individuals should
be discouraged from passing close by the front of the fume hood as
they are likely to cause eddies which eject vapours.
While the sash should offer some protection to the operator, eye protection
should still be worn whenever there is foreseeable risk to the eyes.
Fume hoods are not replacements for safety screens, thus they are not
suitable locations for experiments where there is risk of explosion.
It is safer to use the bench with safety screens and other appropriate
precautions.
There is a temptation to treat any small sink or drip pot in a fume
hood as a disposal point for hazardous liquids. It should be resisted,
even if a fume hood may well be found to be the best place to treat and
dilute these liquids before they are then disposed of in the approved
manner.
|
|
