Laboratory Safety
Incidents: Biological Safety Cabinets
Flame/Ethanol Sterilization
Fires (top)
Clean Bench Fire (top)
An individual was decontaminating the surfaces of a clean bench with
70% alcohol while a bunsen burner was lit. A fire erupted which ended up catching
the filters on fire. Severe damage to the hood and the laboratory occured in 10
minutes. Since a fresh supply of air was delivered to the burning filters....you can
imagine the intensity of the resultant fire.
2 Flaming Loop Fires, both inside a Biosafety Cabinet (top)
Two reported laboratory fires, fueled by natural gas associated with
the use of Bunsen burners should compel researchers to rethink how, and if, they should
use them. Both fires occured at the University of X. Fortunately, no one was
seriously injured.
In one case, gas leaked from a loose tubing connection and
accumulated to where it was ignited by the burner's flame, causing a small explosion.
Isopropanol in a nearby flask inside the cabinet also caught fire.
In the other incident, a researcher inadvertently turned on the gas
thinking he was turning on the vacuum line. Realizing his mistake, he turned off the
gas. When he subsequently attempted to light the burner, the residual gas in the
cabinet ignited, burning his arms (first degree) and singeing his hair. He had not
waited long enough for the gas to dissipate.
Bunsen burners are typically used inside Biological Safety Cabinets
for sterilizing inoculating loops and test tube lips. However, this task can be
accomplished using a small electric "furnace" - a device expressly designed to
eliminate the need for using flammable gas in a safety cabinet (available from Fisher) or
consider using pre-sterilized, disposable loops.) Accidently released gas may also
be ignited by sparks or heat from the motors and switches on cabinet fans and lights.
Consider these four points when using a flame:
* Use a burner equipped with a pilot light, in place of older
models with a blow torch-like flame;
* Do not use latex tubing (the stretchy yellow material).
It tears easily and is prone to pinholes; use butyl rubber instead;
* Check tubing regularly for cracks and tears;
* Replace tubing at the first sign of wear or deterioration.
Flame-Sterilizing Fire Incident (top)
A fire occured when a lab worker was flame-sterilizing
slip-glasses. The slip-glasses were in a small container of ethanol inside a
biosafety cabinet. The slip glasses were being removed, one-at-a-time, with
tweezers as the employee held each one in the flame of a small gas burner unit and then
placed in a holder.
The employee could not see flames but noticed heat emanating
from the supply container holding the unsterilized slip-glasses. She attempted to
extinguish the fire by placing an aluminum-foil cover over the container (the
container’s cover was not available). The aluminum foil cover blew off, so the
employee attempted to cover the container with a petri dish. However, a pipetter in
the cabinet had caught fire (probably due to ethanol spilling into
heat-induced cracks in the container).
She went for a fire extinguisher, only to find upon return that the
door to the room had shut and was locked. She did not have the key. At this
point the employee called 911 and activated the building fire alarm system. Damage was
limited to the interior of the biosafety cabinet and the pipetter. The employee’s
actions in response to this incident were admirable. She initialy attempted to extinguish
the fire; when unable to do so, she called for additional help. The only improvement would
have been if someone else had been able to call 911 and activate the fire alarm while the
first employee was still trying to extinguish the fire. This fire was probably
started by an [invisible] burning drop of ethanol falling into the supply container.
The lessons to be learned for anyone doing similar work are:
1. Position the container of ethanol, supply of slip-glasses
and the destination container so that there is no potential for carrying the sterilized
slip-glasses over it
2. Be sure to have a key on your person at all times for any
room in which you’re working whose latch is set to lock every time the door is
closed.
Unattended Use of Bunsen Burner in
a Biological Safety Cabinet (top)
Recently, a researcher left a lit Bunsen burner inside a BSC, closed
the sash and walked away. The type of biological safety cabinet she was using recirculates
about 70% of the air with 30% of the air goes out the exhaust. When the sash is closed
there is no bypass to allow fresh air into the cabinet. Thus, no exhaust was leaving the
cabinet. Heat within the BSC built up quickly. The situation was discovered only after the
flame had burned for a few minutes. The BSC was hot to the touch on the outside.
1. Experiments with potential danger should never be left
unattended, especially when an open flame is involved.
2. A standard Bunsen burner is only appropriate for open-bench
usage. Inside a BSC, an electric furnace such as a Bacti-cinerator,
or a device such as the Touch-O-Matic
Bunsen Burner should be used. This type of burner is built in a way that a platform is
connected to the burner itself. A flame is only produced when the user's hand rests on the
platform. When the user's hand moves away, only a pilot light burns. Touch-O-Matic Bunsen
Burner also serves the purpose when a continuous flame is needed, the platform only needs
to be pressed and slightly twisted. Consequently, the risk of leaving a full flame on by
accident is reduced.
3. Open flames should not be necessary in the near microbe-free
environment of a biological safety cabinet. On an open bench, flaming the neck of a
culture vessel will create an upward air current which prevents microorganisms from
falling into the tube or flask. In a BSC, however, an open flame creates turbulence which
disrupts the pattern of HEPA-filtered air supplied to the work surface. Disposable sterile
loops (example)
should be considered so no flame sterilization is necessary.
Disclaimer
Revision Date: 5/15/2002
url: http://www2.umdnj.edu/eohssweb/aiha/accidents/BSC.htm
American Industrial Hygiene Association
2700 Prosperity Ave., Suite 250
Fairfax, VA 22031
(703) 849-8888 (703) 207-3561 fax
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