Fume cupboards, laminar flow hoods and biosafety cabinets: which protects what
How fume cupboards, laminar flow cabinets and microbiological safety cabinets work, what each one protects, and which to use for chemicals or microbes.
By Zachery Casey · Published · Reviewed · Editorial policy
Labs use three kinds of ventilated cabinet that look similar from the front: a glass sash or window, a work surface and a fan. They do very different jobs, and using the wrong one can put the user or the work at risk. A fume cupboard protects the person from chemical vapours. A laminar flow cabinet protects the work from dust and microbes, and doesn't protect the person at all. A microbiological safety cabinet, called a biosafety cabinet in the US, is designed for biological material and can protect both. This guide explains how each one works and when to use it.
Terms are defined in the glossary.
Three questions to ask
Every ventilated cabinet can be judged by what it protects:
| Protects the user? | Protects the work? | Protects the room? | |
|---|---|---|---|
| Fume cupboard | Yes, from vapours and fumes | No | Yes, if ducted outside |
| Laminar flow cabinet | No | Yes | No |
| Class I microbiological safety cabinet | Yes | No | Yes |
| Class II microbiological safety cabinet | Yes | Yes | Yes |
| Class III microbiological safety cabinet (glove box) | Yes, fully enclosed | Yes | Yes |
The right choice depends on the hazard. Chemical vapours need a fume cupboard. Sterile work with nothing hazardous can use a laminar flow cabinet. Biological agents need a safety cabinet of the right class.
Fume cupboards (fume hoods)
"Fume cupboard" is the UK name. In the US the same thing is called a fume hood.
How a fume cupboard works
A fan, usually on the roof, pulls air into the cupboard through the front opening. The air sweeps across the work surface, picks up vapours, gases and fine dust, and leaves through a duct to the outside. The steady flow into the opening is what keeps fumes from escaping towards the user.
- The sash is the sliding glass front. Keeping it low makes the opening smaller, speeds up the inflow and puts a shield between the user and the work. Most cupboards are marked with a maximum working height.
- Baffles at the back spread the airflow so that heavy and light vapours are both drawn out.
- An airflow alarm warns when the flow drops too low to give protection.
The speed of air through the front opening, called the face velocity, is often around 0.3–0.5 m/s. The current European standard, BS EN 14175, judges a cupboard by how well it actually contains a test gas rather than by face velocity alone.
Ducted and recirculating
- Ducted cupboards send the air outside. They handle the widest range of chemicals.
- Recirculating (filtered) cupboards pass the air through activated carbon filters and return it to the room. They suit only a known, limited range of chemicals that the filters can trap, and the filters need monitoring and replacing.
Using one well
- Work at least 15–20 cm inside the opening, not at the front edge.
- Keep the sash as low as practical.
- Don't crowd the cupboard with bottles and equipment. Clutter disturbs the airflow.
- Avoid fast movements and people walking past, which pull air back out of the opening.
- Don't use it as a store for open containers. Chemicals belong in a suitable storage cabinet; see storing lab chemicals safely.
A fume cupboard gives no protection to the work from dust or microbes in the room, because unfiltered room air flows straight across it.
Laminar flow cabinets
A laminar flow cabinet, also called a laminar flow hood or clean bench, does the opposite job. A fan pushes room air through a HEPA filter and blows the clean air in a smooth, even stream across or down onto the work surface. "Laminar" means the air moves in parallel layers rather than swirling, so particles are swept away instead of settling on the work.
- Horizontal flow cabinets blow the air from the back of the cabinet straight towards the user.
- Vertical flow cabinets blow it down from the top onto the work surface, and it leaves at the front.
Either way, the air ends up in the user's face or in the room. That is why a laminar flow cabinet protects the work but never the user. Anything powdered, volatile, toxic or biological handled in it is blown towards the person using it.
Laminar flow cabinets are used for preparing sterile media, handling sterile consumables and other work where keeping dust and microbes out matters and the material itself is harmless.
HEPA filters
HEPA stands for high-efficiency particulate air. A HEPA filter traps at least 99.97% of particles 0.3 µm across, the size that is hardest to catch. Larger and smaller particles are trapped even more efficiently. In Europe, filters are graded under EN 1822, with H13 and H14 the classes used in cabinets.
HEPA filters stop particles, including bacteria and spores. They don't stop gases or vapours, which pass straight through.
Microbiological safety cabinets (biosafety cabinets)
"Microbiological safety cabinet" (MSC) is the UK and European name. "Biosafety cabinet" (BSC) is the US name for the same equipment. They are built for work with biological agents, such as bacteria, viruses and cell cultures, and are graded into three classes under BS EN 12469.
Class I
Room air is drawn in through the front opening, across the work and out through a HEPA filter. The inflow protects the user and the filtered exhaust protects the room. The work isn't protected, because unfiltered room air passes over it.
Class II
The most common type in labs. It combines two airflows:
- Inflow through the front opening, which protects the user.
- HEPA-filtered downflow from the top onto the work surface, which protects the work.
The two streams meet at a grille just inside the front and are drawn away. Part of the air is HEPA-filtered and recirculated, and part is HEPA-filtered and exhausted. Class II cabinets are the standard for cell culture, because the cells need protecting from contamination and the user needs protecting from anything the cells carry. See aseptic technique for working practice inside one.
Class III
A fully sealed, gas-tight cabinet. The user works through thick gloves fixed to ports in the front, and materials pass in and out through an airlock or a dunk tank. Class III cabinets are used for the most dangerous biological agents.
What a safety cabinet doesn't do
A safety cabinet's HEPA filters trap particles, not vapours. Volatile or toxic chemicals used inside one can pass through the filters and, in a recirculating cabinet, build up inside it or return to the room. Only small amounts of volatile chemicals should be used in a safety cabinet unless it is specifically ducted for them. Chemical work belongs in a fume cupboard.
Choosing the right cabinet
| Work | Use |
|---|---|
| Volatile solvents, acids, corrosive or toxic vapours | Fume cupboard |
| Weighing fine, hazardous powders | Fume cupboard or a ventilated balance enclosure |
| Preparing sterile media or consumables with no hazard | Laminar flow cabinet, or a Class II safety cabinet |
| Cell culture | Class II microbiological safety cabinet |
| Work with bacteria or viruses | The safety cabinet class that the risk assessment calls for |
| Hazardous chemicals that must also be kept sterile | Usually a microbiological safety cabinet ducted to the outside and rated for the chemicals involved, or a sealed glove box; the risk assessment decides which |
The deciding step is the risk assessment. Under COSHH, the employer assesses the hazard and chooses controls, and ventilated enclosures are one of the main engineering controls. The safety data sheet for each reagent says what exposure controls it needs, and the hazard symbols on its label are a quick first guide.
Testing and maintenance
In the UK, fume cupboards and safety cabinets used to control exposure count as local exhaust ventilation (LEV). COSHH requires them to be thoroughly examined and tested, normally at least every 14 months, with records kept (HSE). HSE's guide HSG258 sets out how LEV should be designed and tested (HSE, HSG258).
Between tests, users should:
- check the airflow indicator or alarm before each use,
- report a cupboard that smells, whistles or feels weak, and
- for safety cabinets, follow the schedule for HEPA filter integrity testing, usually done by a specialist engineer.
A laminar flow cabinet isn't an LEV control, because it doesn't protect anyone. Its filters still need regular checks to make sure they protect the work.
Related guides
For the law on hazardous substances and what a safety data sheet contains, see COSHH and safety data sheets. For working sterile, see aseptic technique and autoclaving. For handling powders that take up water from the air, see hygroscopic powders. Each product page has a safety data sheet link in its resources, or says the sheet is available on request. For the protective equipment worn alongside these controls, see lab gloves and eye protection.
This guide gives general information. It isn't a substitute for your organisation's own risk assessment or the cabinet maker's instructions.
More on lab equipment and safety
- Autoclaves and aseptic technique in the laboratoryHow an autoclave sterilises with steam, cycle times and indicators, autoclave vs dry heat vs filter sterilisation, and the core habits of aseptic technique.
- COSHH and safety data sheets: what they mean for laboratory reagentsCOSHH explained: what it stands for, how a COSHH assessment works with an example, the eight principles of control, and the 16 sections of a safety data sheet.
- Hazard symbols explained: the COSHH and GHS pictogramsWhat each of the nine hazard symbols on a chemical label means, the hazard statements that go with it, and how to handle a chemical that carries it.