What are they?
Essentially, fume cupboards, carbon-filtered cabinets and Class I and
II biological safety cabinets are open-fronted units. They work by sucking
air from the laboratory, past the worker standing in front of the unit,
over the working surface where the airborne contaminants are likely to
be generated and pushing the air into the environment (back into the laboratory
or outside the building depending on the type of unit).They are designed
to remove airborne contaminants (be they gases, vapours, fumes, smells,
dusts or aerosols) from the working environment before they can be breathed
in by workers or their colleagues. They should also be capable of greatly
reducing the concentration of any dangerous components before the air
is vented to the environment.
They are not;
They are not capable of containing 100% of the material generated within
the units themselves - some may escape through the open front. Only units
where the exhaust air is filtered have the capability to remove (or significantly
reduce the concentration of) the components before the air is vented to
Operator protection factors
Open-fronted cabinets can never guarantee to prevent
all airborne material from escaping into the laboratory. For general
purpose work the minimum average air velocity should be 0.5 m/s at
the working face.
They should be capable of providing a minimum measurable
performance under standardised conditions. With biological safety
cabinets there is a test procedure in BS 5726 involving the release
of a potassium iodide aerosol inside the cabinet and detectors positioned
outside the front opening. The "KI-Discus" test
should indicate that no more than 1 particle in every 100,000 released
inside the cabinet escapes to be detected.
Thus the minimum "operator protection factor" (OPF)
for Class I and II biological safety cabinets is given as 105.
The test can be used in fume cupboards and carbon-filtered units but
has not yet been adopted in their standards. There is a containment
test involving sulphur hexafluoride for fume cupboards and results
from this have been reported as comparable to those generated by the
Operator protection will be reduced if the air flow
falls below, or rises above, certain values. This can happen;
if the working surface is cluttered,
if rapid movements are made across the open face
of the cabinet,
if large volumes of gases/vapours are released
into the cabinet or
if the units are not maintained adequately.
Checks and maintenance considerations
COSHH Regulations all facilities provided to control exposure to hazardous
substances must be tested at least once every 14 months and maintained
in good order.
Estates department maintain the ducted fume cupboards.
Our Department ensures the carbon-filtered units and
biological safety cabinets are checked twice a year by an external
checks are made to ensure the average face velocity on these units
Carbon filters can be checked when necessary by using
an electronic vapour detector.
are checked by a smoke of vegetable oil (the test used to be performed
with DOP (di-iso octyl phthalate)). This is performed by the contractor
during the 6-monthly checks.
- Biological safety cabinets used for bio-containment should becontainment-
tested at least once every 14 months (COSHH) by contractors using the
With ducted units that withdraw volumes of air from
laboratories the need to make up such volumes should have been addressed
at the design stage of the building. In Building 4 South such considerations
were made. In some buildings (but not 4S) the heat used to warm the
lab air is reclaimed before the air is exhausted to the environment.
Without such reclamation of heat the financial cost of lost energy
When the fire alarm in Building 4S is activated the
entire air-handling system is shut down (to reduce the spread of smoke
and flames). As the fume cupboard air extract system is an integral
part of the building’s air-handling arrangement,
fume cupboards will stop functioning in the event of a fire alarm
(but not a scheduled practice). When the alarms are reset the fume
cupboards start up again.
Ducted units (fume
cupboards and safety cabinets) must have the exhaust fans sited as far
away from the cabinets as practicable. This is usually on the roof of
the building. This ensures that if the ducting develops a leak then air
will be sucked into the duct (under negative pressure). If the ducting
was under positive pressure any air in the duct would leak out into the
building along with possibly dangerous contaminants.
Green Scafftag in place - Safe to use cabinet - - - - - - Scafftag removed
- do not use cabinet
All fume cupboards, carbon-filtered cabinets and biological safety cabinets
in the Department have a "Scafftag" holder stuck to them. These hold a
green-coloured insert to indicate the unit can be used. If, for any reason,
the green insert (or the holder) has been removed DO NOT USE THE UNIT.
Air flow patterns (pictures from Dynamic Plastics Ltd.)
Ducted Fume Cupboards
(refer also to UoB
SM section 4.2.5).
They draw air from the laboratory and over the work being performed in
the cupboard, carrying gases, vapours, fumes and dusts away from the work
environment through a duct to the roof of the building. There a fan blows
the air up through a chimney and discharges it at high velocity 3 metres
above the roof. They are designed to eliminate or
greatly reduce the risk from chemical and dust hazards generated by your
work. All the 8 ducted fume cupboards (also called fume hoods)
in Building 4 South are designed to conform to the standards detailed
in the British Standard BS7258:1994.
Because fume cupboards are ducted they are fixed in position and, for
all practical purposes, cannot be moved.
All the 4S fume cupboards have water-spray scrubbers fitted. These
can be effective at removing dusts, smoke, acid fumes and water-miscible
organic solvent vapours. They are operated either by pressing the SCRUBBER
START membrane key or switching on the SCRUBBER switch in the refurbished
units (in 1.28, 1.37, 1.37A and 1.48). (New fume cupboards in building
5 West are equipped with carbon filters. In 1 South (the Chemistry research
building) the exhaust from the fume cupboards is not filtered, nor is
any heat reclaimed from it.)
Relative positions of water spray scrubbers at rear of
(courtesy of Dynamic Plastics Ltd..)
Points to be aware of;
The fans are on all the time and cannot be switched
off by lab workers.
They will be shut down in the event of a fire alarm
(not a scheduled fire alarm practice).
If the fume cupboard alarm sounds do not use it. It
means the airflow has fallen below an acceptable level because either
the fan has failed or the sash has been raised above its maximum recommended
working height. If the alarm sounds when the sash is lowered please
contact either Ray Dickson or Chris Davey.
Most of the cupboards (i.e. all except those in 0.58,
0.76, 1.28 and 1.48) have a scrubber liquor sampling tap (green with
RED and blue inner) on the left side of the fascia and a drain
cup (on the left of the work surface) leading to the scrubber liquor
tank. The tap does NOT supply cold water and the drain cup must
NOT be used as a waste drain.
Carbon Filter cabinets
What they are not !!
They are not conventional fume cupboards and
certainly not biological safety cabinets. (Even they
are not necessarily guaranteed to be 100% effective at protecting the
operator (or the work)). They are not laminar flow work
stations. The accepted British standard for manufacture and performance
of these units is BS7989:2001
What are they ?
Essentially mobile units that draw air from the lab over the
work, through a dust filter, a carbon filter (and/or possibly a HEPA
filter) and exhaust the air back into the laboratory. They are designed
to DRAMATICALLY REDUCE the airborne concentration of a range of chemical
vapours, fumes, smells and dusts in air to acceptable levels. They can
mop up low levels of some vapours and fumes very efficiently, but they
might not cope well with gross spillages or boiling off solvents or acids.
They are cheaper than conventional ducted fume cupboards BUT
THEY ARE NOT A SUBSTITUTE FOR THEM. There are prefilters on
all the units to take out 99% of dusts, mists and aerosols in the range
0.5 micron to 2 micron (and hold them there when the fans are switched
off). (The HEPA filter on the powder weighing unit (in lab 1.52) is designed
to take out more than 99.997% of particles of 0.2 micron size.)
Activated carbon will adsorb any organic chemical with a molecular weight
above 30 and a boiling point above 60'C. However, not all chemicals
are absorbed with the same tenacity. The carbon filters can be specifically
tailored to give several types for adsorbing particular substances more
effectively. The 14Kg filter block can adsorb nearly half its own weight
of some solvents and the filtration efficiency can approach 100%. The
filter beds can be made with a combination of different types of carbon
(e.g. ACI and SUL). Refer to this table for the
optimum type of filter for a particular compound.To achieve optimum filtration
efficiency and capacity, important design criteria must be met by the
filtration equipment. The air must take at least 0.3 seconds ("dwell"
time) to pass through the carbon.
How do they work ?
Average face velocity required to capture most releases
of low hazard material is generally regarded to be 0.5 metres/second.
Prefilter for large dust particles. Works by strong
electrostatic forces generated by the fibres of the "Filtrete" prefilter.
Main carbon filter dwell time is at least 0.3
seconds, the air flows through it at a rate of 0.3m/s
Filtration takes place in an active filter zone
is exhausted to lab (can also be ducted)
Carbon filter efficiency will fail rapidly
What you can do in them.
Essentially, work activities (other than simply
smelly work) performed in these units must be assessed with the Department’s
risk assessment scheme.
most "smelly" chemicals.
General dispensing of most organic solvents and acids
that you are likely to use.
The powder weighing unit in SB 1.52 can be used for
weighing of powders in still air followed by purging.
What you must not do in them.
Do not boil or evaporate large volumes of organic
solvents or acids.
Do not work with highly toxic materials.
Do not work with pathogenic micro-organisms or genetically
Do not leave any spillages in the units.
How do you know they are working
How is performance tested ?
Users can check the manometer on a daily basis. 6-monthlycheck on
face velocity by Department staff. 6-monthly check of carbon filters (and
HEPA filter in powder weighing unit) by contractor.
Table to determine optimum carbon
filter type to be used to adsorb specific chemical vapours.
The range of materials capable of being filtered by carbon filters can
be viewed on this web site; http://www.aaceurovent.co.uk/mediaindex.htm
Chemicals marked * are poorly adsorbed by all filters and should be used
only in small quantities. However, their exhaust concentrations will be
considerably lower than the input concentration due to retardation in
the filter matrix (chromatography effect).
The information below was supplied by Astec-Microflow of Weston-Super-Mare.
Acetic anhydride, Acrylic, Butyric, Caprylic, Carbolic, Lactic, Osmium tetroxide,
Palmitic, Phenol, Proprionic, Valeric
Amyl, Butyl, Cyclohexanol, lsopropyl, Methyl (methanol), Propyl
lso-butane, Butylene, Butadiene*, Cyclohexane, N-decane*, Ethane*, Ethylene*,
N-heptane*, Heptylene*, Hexane, Hexylene*, Methane' N-nonane* N-octane*,
N-octylene*, Pentane, Propane*, Propylene
Napthalene, Ninhydrin, Styrene monomer, Toluene, Toluidine, Xylene
acetate, Cellosolve acetate, Ethyl acetate, Ethyl acrylate, Ethyl formate,
lsopropyl acetate, Methyl acetate, Methyl acrylate, Methyl methacrylate
Acrolein, Benzaldehyde, Butyraldehyde, Caproaldehyde, Crotonaldehyde, Cyclohexanol,
Diethyl ketone, Dipropyl ketone, Mesityl oxide, Methyl butyl ketone Methyl
isobutylketone, Propionaldehyde, Valeraldehyde, Valeric aldehyde
Butyl, Cellosolve, Dioxan, Ethylene oxide, lsopropyl, Propyl
Butyl chloride, Carbon tetrachloride, Chlorine, Chlorobenzene, Chlorobutadiene,
Chloroform, Chloro picrin, Chloro nitropropane, Dibromo-ethane, Dichlorobenzene,
Dichlorodifluoro methane, Dichlorodifluoro ethane, Dichloro ethyl ether,
Dichloromethane, Dichloro monofluoro methane, Dichloropropane, Dichloro
tetrafluoro ethane, Ethyl bromide, Ethyl chloride, Ethylene dichloride,
Fluorotrichloromethane, Freon (BP > -20oC), Iodine, lodoform,
Methyl bromide, Methyl chloride, Methyl chloroform, Methylene chloride,
Monochlorobenzene, Fluoratrichloromethane, Paradichlorobenzene, Perchloroethylene,
Propyl chloride, Tetrachloroethane, Tetrachloroethylene, Vinyl Chloride
bromide, Hydrogen chloride, Hydrogen iodide,
disulphide, Dimethyl sulphate, Tetrahydrothiapene
mereaptan, Hydrogen sulphide, Mercaptans-(high MW),
dioxide, Sulphur trioxide, Sulphuric acid,
Amines- (low MW), Amines-(high MW), Diethyl amine, Dimethyl amine, Ethyl
Diethyl aniline, Indole, Nicotine, Nitrobenzene, Nitroethane, Nitroglycerine,
Nitromethane, Nitrotoluene, Urea, Uric acid
acid fumes, Nitrogen dioxide*,
Camphor, Carbon monoxide*, Carbon dioxide*, Citrus fruits, Cooking odours,
Deodorisers, Detergents, Leather, Ozone, Nicotine, Perfumes, Petrol, Resins,
odours, Toilet odours
odours, Human odours, Putrescine,
Biological Safety Cabinets (refer
also to UoB
SM section 4.2.7)
For a useful review "Appraisal of the practical effectiveness of
biosafety controls in biotechnology with special reference to safety cabinets"
by Ray Clark refer to https://tspace.library.utoronto.ca/retrieve/273/by95003.pdf
(BioSafety Volume 1, Paper 3 (BY95003), May 5th 1995).
Biological safety cabinets are designed to conform
to British Standard BS5726 and are validated to BS EN 12469:2000
(including containment using KI-discus equipment).
Bio-exclusion or bio-containment?
For work involving hazardous biological agents these safety cabinets are
used for bio-containment - they should contain the hazard from escaping
into the environment. Cabinets can be tested for containment using the
"KI-Discus" test. The minimum acceptable containment standard
is to provide an operator protection factor of 10E5.
For non-hazardous tissue culture work they are used for bio-exclusion
- to minimise the chance of contaminating the work in progress by excluding
viable organisms from the laboratory air.
For either mode, HEPA filters and carefully controlled laminar air flows
are utilised to effect both.
biological safety cabinets use HEPA
filters to clean air of aerosols and other fine particles but will dump
any smells generated by the work into the laboratory.
(High Efficiency Particulate Air) filters
can be rendered useless if they become wet or if they are physically damaged.
The only way to test their integrity is to challenge them with an oil
smoke and test the effluent air with a sensitive spectrophotometer. The
Department does not have the equipment to do this.
HEPA filters should be protected from gross dust blockage by incorporating
a prefilter. This should be cleaned or replaced on a regular basis.
They draw air over the work being performed in the cabinet, through a
HEPA filter to be discharged either back into the laboratory or outside
They are designed to eliminate or greatly reduce the risk from microbiological
hazards generated by your work.
If safety cabinets are being used with pathogenic micro-organisms then
arrangements must be made to decontaminate the units before any servicing
or repair work is carried out and before they are moved. Formaldehyde
fumigating units can be provided by manufacturers. Such units are in place
on the cabinets in labs 0.47b and 1.14.
If a gas supply is required in safety cabinets then an electrically-operated
solenoid valve should be fitted as on the cabinets in labs 0.43b, 1.14,
1.28b, 1.37b (MDH) and 1.45a.
Class I safety cabinets protect workers
and the work environment from microbiological hazards (OPF>10E5).
They do not protect the work from contamination. If the exhaust is double-HEPA
filtered then the exhaust can be vented back into the laboratory. There
is a double-HEPA filtered Class I safety cabinet in lab 1.52.
Class II safety cabinets protect both the work, workers (OPF>10E5)
and the environment. The work area is bathed with a vertical flow of HEPA-filtered
air. Air is also drawn, from the lab, downwards through the front opening
of the cabinet. Underneath the perforated work surface the air from the
lab is mixed with air passing over the work. That is then drawn through
a dust pre-filter and a fan and about 20% of the air is HEPA filtered
and vented either outside the building or back into the lab (if double-HEPA
filtered). Older Class II cabinets (such as most of ours) may vent air
back into the lab after only a single HEPA filtration. The remaining 80%
is used to bathe the work area. There are Class II safety cabinets in
labs 0.43b, 0.47a, 0.70 (2), 0.71, 1.14, 1.37b and 1.45a although not
all are used for containment of pathogenic organisms.
Class III safety cabinets are totally enclosed and workers
perform their work using glove ports. They are used for work with highly
pathogenic organisms. The chamber is maintained at a negative pressure,
air enters via a HEPA filter, materials can only enter the cabinet through
an air-lock and the exhaust air is HEPA filtered before discharging outside
the building (never back into the lab).
We do not have any Class III cabinets in the Department.
Microbiological safety cabinets (from
Dr R.P. Clark and Science Reviews Ltd.)
is tested by;
- Checking face velocity
of Class I and II cabinets.
- Challenging HEPA filters
with oil smoke.
- Checking operator protection
factor in Class I and II cabinets used for bio-containment using the
- Checking integrity
of ducting at least once every 14 months.
KI-Discus test being performed on a Class II biological safety cabinet
(this one failed)
Tissue culture cabinets
These may be designed along the lines of, or may be identical to, Class
II biological safety cabinets. However, if they are
- not to be used with hazardous micro-organisms and are
- solely to be used for non-GM tissue culture workthen they should
- derogated and classified and labelled, as "Tissue culture cabinets.
Not for use with hazardous micro-organisms or GMOs"
- and any biohazard warning sign removed.
In this way there should be no confusion about conducting hazardous work
in them.Two such cabinets are in 1.28b and 1.37b.
THESE ARE NOT SAFETY CABINETS
Laminar Flow Work Stations
Never confuse these laminar flow work stations (LFWS) with cabinets designed
to protect the worker from hazardous airborne contaminants. LFWS operate
by blowing HEPA filtered air over the work surface. Horizontal flow cabinets
blow the air onto the worker and into the lab, thus if any hazards are
generated in the cabinet they will be deposited onto the worker and into
the lab air! They can be used for aseptic manipulations and for working
on non-sporulating and non-hazardous biological materials.
What have we got and where are they?
Information correct as of January 2001.
cupboards operating at a minimum face velocity
of 0.5 m/s
||0.52, 0.53, 0.58, 0.76, 1.28,
1.37, 1.37a and 1.48.
fume cupboards operating at a minimum face velocity of 0.65
units (and filter combinations - refer to previous
table). All these units recirculate filtered air back into the laboratory.
1.07 (ACI/AMM/SUL), 1.14 (ACI/AMM/SUL),
1.15 (4 units - ACI/SUL, ACI/ETH, ACI/CYN, ACI/ACR/AMM),
1.45 (ACI/AMM/SUL), 1.52 (ACI/AMM/SUL)
||SB annexe (1 ducted unit with
ACR filter for 125I)
II biological safety cabinets (All our units are single-HEPA
filtered with air recirculated back into the lab.)
||0.43b (MDH gas), 0.47b (MDH
formaliser), 0.52 (MDH gas and formaliser), 0.70 (2 x MAT), 0.71 (Tecnoflow),
1.37b (MAT), 1.45a (MDH gas),
weighing booth (with filtered air recirculated back into the
Laminar flow work stations (not
safety cabinets). (These blow air over the work, the operator
and into the laboratory).
|Horizontal air flow
||0.39 (2 units), 0.53, 0.70
(2 units), 0.71, 1.07, 1.14, 1.21a (2 units) , 1.23 (2 units), 1.33, 1.52
(2 units), Manducary
|Vertical air flow
||0.43b, 1.23, 1.45a