Biology Safety Wiki
FUM3.2 – Fume cupboards and safety cabinets
General considerations for fume cupboards and safety cabinets;
What they are
What they aren't!
Operator protection factors
Checks and maintenance considerations
Air make up
Ducted units
Scafftags
Ducted fume cupboards
Scrubbers
Points to be aware of
Carbon Filtered cabinets
What they are not!
What are they?
Carbon filters
How do they work?
What you can do in them
What you must not do in them
How do you know they are working?
How is their performance tested?
Table of filter type for optimum chemical vapour
Biological Safety cabinets
Bio-exclusion or bio-containment?
Recirculating biological safety cabinets
HEPA filters
Performance checks
Tissue Culture cabinets
Laminar Flow Work Stations
What cabinets have we got, and where are they?
What are they?
Essentially, fume cupboards, carbon-filtered cabinets and Class I and II biological safety cabinets are open-fronted
cupboards or cabinets. 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 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 the environment.
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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 inward 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
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"operator protection factor" (OPF) for Class I and II biological safety cabinets is given as 10 . 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 (SF6) for fume cupboards and results from this have been reported as
comparable to those generated by the "KiDiscus" test.
 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,
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FUM3.2. Fume cupboards and safety cabinets
if large volumes of gases/vapours are released into the cabinet or
if the units are not maintained adequately.
Checks and maintenance considerations
 Under the 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.
 The University Estates department maintain the plant associated with ducted fume cupboards.
 Our Department ensures the carbon-filtered units and biological safety cabinets are checked twice a year by
an external contractor.
 Regular checks are made to ensure the average face velocity on these units is adequate.
 Carbon filters can be checked when necessary by using an electronic vapour detector.
 HEPA filters 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 be containment- tested at least once every 14
months (COSHH) by contractors using the KI-Discus test.
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Air make-up
 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
as the ducted fume cupboards are on all the time. 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 is significant. In Building 3 South the ducted fume cupboards can be switched off.
 When the fire alarm in Building 3S or 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 buildings’ airhandling 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 (as it is 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.
Scafftags
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.
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Ducted Fume Cupboards (also called fume hoods)
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 10 ducted fume cupboards in the
department 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.
Scrubbers
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).
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Points to be aware of;
 The fans of the 4S ducted fume cupboards are on all the time and cannot be switched off by lab workers.
 The fans of the 3S ducted fume cupboards can be switched on and off by lab workers.
 They will all be shut down in the event of a fire alarm (not a scheduled fire alarm practice).
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FUM3.2. Fume cupboards and safety cabinets
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
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 [email protected].
Most of the ducted cupboards in 4S (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 Filtered 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.)
Carbon Filters
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. Most cabinets in the department are fitted with a standard EDU filter. 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.
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How do they work ?
 Remember operator protection factors for fume cupboards and biological safety cabinets?
 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
 Air is exhausted to lab (can also be ducted)
 Carbon filter efficiency will fail rapidly
What you can do in them
 Use of 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.
Essentially, work activities (other than simply smelly work) performed in these units must be assessed with the
Department’s risk assessment scheme.
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What you must not do in them
 Do not boil or evaporate large volumes of organic solvents or acids.
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FUM3.2. Fume cupboards and safety cabinets
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Do not work with highly toxic materials.
Do not work with pathogenic micro-organisms or genetically modified organisms.
Do not leave any spillages in the units.
How do you know they are working ?
 Green Scafftag insert should be displayed.
 Manometer (if fitted) should indicate a good seal around the filter, adequate air velocity across the working
face and also when the prefilter is getting clogged with dust. The dust filter efficiency will fail rapidly.
 In the laboratory there should be a general absence of smell of compounds in use in cabinet.
How is performance tested ?
6-monthlycheck on face velocity and condition of carbon filters (and HEPA filter in powder weighing unit) by contractor.
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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 requested from http://www.astecmicroflow.com/Astec/index.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.
CHEMICAL TYPE
Acids
Acetic, Acetic anhydride, Acrylic, Butyric, Caprylic, Carbolic, Lactic, Osmium tetroxide, Palmitic, Phenol,
Proprionic, Valeric
Formic
Alcohols
Ethyl, Amyl, Butyl, Cyclohexanol, lsopropyl, Methyl (methanol), Propyl
Aliphatic Hydrocarbons
Acetylene, lso-butane, Butylene, Butadiene*, Cyclohexane, N-decane*, Ethane*, Ethylene*, N-heptane*,
Heptylene*, Hexane, Hexylene*, Methane' N-nonane* N-octane*, N-octylene*, Pentane, Propane*,
Propylene
Aromatic hydrocarbons
Benzene, Napthalene, Ninhydrin, Styrene monomer, Toluene, Toluidine, Xylene
Esters
Butyl acetate, Cellosolve acetate, Ethyl acetate, Ethyl acrylate, Ethyl formate, lsopropyl acetate, Methyl
acetate, Methyl acrylate, Methyl methacrylate
Aldehydes and Ketones
Acetone, Acrolein, Benzaldehyde, Butyraldehyde, Caproaldehyde, Crotonaldehyde, Cyclohexanol, Diethyl
ketone, Dipropyl ketone, Mesityl oxide, Methyl butyl ketone Methyl isobutylketone, Propionaldehyde,
Valeraldehyde, Valeric aldehyde
Acetaldehyde, Formaldehyde, Gluteraidehyde,
Methyl ethyl ketone,
Ethers
Amyl, Butyl, Cellosolve, Dioxan, Ethylene oxide, lsopropyl, Propyl
Diethyl (ethyl), Methyl*,
Halogens
Bromine, 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
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FILTER
A/C
ACI
A/C
A/C
A/C
A/C
A/C
FOR
ACI
A/C
ETH
A/C
FUM3.2. Fume cupboards and safety cabinets
CHEMICAL TYPE
Hydrogen bromide, Hydrogen chloride, Hydrogen iodide,
Phosgene,
Sulphur compounds
Carbon disulphide, Dimethyl sulphate, Tetrahydrothiapene
Ethyl mereaptan, Hydrogen sulphide, Mercaptans-(high MW),
Sulphur dioxide, Sulphur trioxide, Sulphuric acid,
Nitrogen Compounds
Acetonitrile, Hydrogen cyanide,
Ammonia, Amines- (low MW), Amines-(high MW), Diethyl amine, Dimethyl amine, Ethyl amine, Pyridine,
Aniline, Diethyl aniline, Indole, Nicotine, Nitrobenzene, Nitroethane, Nitroglycerine, Nitromethane,
Nitrotoluene, Urea, Uric acid
Nitric acid fumes, Nitrogen dioxide*,
Miscellaneous
Adhesives, Camphor, Carbon monoxide*, Carbon dioxide*, Citrus fruits, Cooking odours, Deodorisers,
Detergents, Leather, Ozone, Nicotine, Perfumes, Petrol, Resins,
Animal odours, Toilet odours
Hospital odours, Human odours, Putrescine,
FILTER
ACI
MIL
A/C
SUL
ACI
CYN
AMM
A/C
ACI
A/C
OAL
OAC
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Biological Safety Cabinets
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"
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test. The minimum acceptable containment standard is to provide an operator protection factor of 10 .
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.
Recirculating 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. They should have 2 HEPA filters in series.
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HEPA (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 the building.
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.
The contractors who check the units can use vapour-phase hydrogen peroxide (VPHP) to effect decontamination, but
efficacy tests must be performed to determine that VPHP is effective.
If a gas supply is required in safety cabinets then an electrically-operated solenoid valve should be fitted.
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.
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FUM3.2. Fume cupboards and safety cabinets
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.
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.
Performance is tested by;
 Checking face velocity of Class I and II cabinets.
 Contractors challenging HEPA filters with oil smoke.
 Checking operator protection factor in Class I and II cabinets used for bio-containment using the "KI-Discus"
test.
 Checking integrity of ducting at least once every 14 months.
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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 work then they should be;
 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.
Laminar Flow Work Stations
THESE ARE NOT SAFETY CABINETS
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.
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What have we got and where are they? Information correct as of January 2001.
4S 0.52
4S 0.53
4S 0.58
4S 0.76
4S 1.28
4S 1.37
4S 1.37a
4S 1.48
3S 1.09
3S 1.13
4S 0.33 (AC/ACI)
4S 0.34 (ACR)
4S 0.39D (ACI)
4S 0.43 (ACI),
Carbon-filtered units
4S 0.73 (ACI/SUL/CYN)
4S 1.07 (ACI/AMM/SUL)
4S 1.14 (ACI/AMM/SUL)
(and filter combinations - 4S 0.47 (FOR)
refer to previous table).
4S 1.15 (4 units – ACI/SUL, ACI/ETH, ACI/CYN,ACI/ACR/AMM)
All these units recirculate 4S 1.23
4S 1.33 (AC/ACI)
4S 1.37 (AC)
4S 1.45 (ACI/AMM/SUL)
filtered air back into the
(ACI/CYN)
laboratory.
4S 1.52 (ACI/AMM/SUL)
4S 0.43b (MDH gas)
4S 0.47b (MDH formaliser)
4S 0.52 (MDH gas + formaliser)
Class II biological safety cabinets (All
our units are single-HEPA filtered with
4S 0.70 (2 x MAT)
4S 0.71 (Tecnoflow)
4S 1.37b (MAT)
air recirculated back into the lab.)
4S 1.45a (MDH gas)
Powder weighing booth (with filtered air recirculated back into the lab..)
4S 1.52
Laminar flow work stations (not safety cabinets). (These blow air over the work, the operator and into the laboratory).
4S 0.39 (2 units),
4S 0.53
4S 0.70 (2 units)
4S 0.71
4S 1.07
4S 1.14
4S 1.21a (2 units) 4S 1.23 (2 units)
Horizontal air flow
4S 1.33
4S 1.52 (2 units),
Vertical air flow
04S.43b,
4S 1.23,
4S 1.45a
Ducted fume cupboards operating at a minimum face velocity of 0.5
m/s
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FUM3.2. Fume cupboards and safety cabinets