Fume Cupboards:

Guidance for Safe Use of Laboratory Fume Cupboards

April 2018

Occupational Health and Safety Service

HSD029C (rev 4)

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Guidance for Safe Use of Laboratory Ducted Fume Cupboards

1 INTRODUCTION

Fume cupboard systems are the most common engineering control measure employed within the University for the prevention of exposure to hazardous substances. The legislation governing their use and the understanding of how they arrest and contain contaminants has developed significantly over the last few years. It is the intention that this code of practice and guidance will establish a common operating procedure throughout the University in order to meet all statutory obligations.

This code of practice and guidance is for anybody whose work involves using a fume cupboard and for those with delegated duties in departments such as the Departmental Safety Officer (DSO).

This document does not cover the use of laminar flow cabinets or microbiological cabinets, however limited guidance is included on the use of recirculating fume cupboards and HEPA filtered chemical powder handling cabinets (see section 3).

2 LEGISLATION

There are explicit requirements in the Control of Substances Hazardous to Health Regulations (as amended) to prevent exposure of employees (and others who might be affected) to hazardous substances, and where this is not possible, to adequately control exposure. The law also requires the assessment of these hazards and risks and identification of measures to prevent or control them before work is carried out.

Where necessary control can be achieved by measures such as Local Exhaust Ventilation (LEV): the classification of mechanical ventilation devices in which laboratory fume cupboards are placed.

The regulations establish the requirement for LEV systems to be maintained in an efficient state, efficient working order, good repair and clean condition. They are also subject to thorough examination and testing at periods not greater than fourteen months (annual testing is the norm), and more frequently if the assessment identifies higher risk. There is a specific requirement for users of fume cupboards to make weekly checks of certain functions of the system, and to report any faults to management as soon as is reasonably possible.

In addition, the design and manufacture of fume cupboards is controlled and regulated by British Standards (BS 7258, Parts 1, 2, 3 and 4 – which apply to fume cupboards installed in the work place prior to 2004, and BS EN 14175, Parts 1, 2, 3, 4, 5 and 6 for fume cupboards installed from 2004).

3 MINIMUM DESIGN SPECIFICATION FOR FUME CUPBOARD SYSTEMS

3.1 Safety and System Performance

A fume cupboard is a key protective and control device in laboratories where chemicals are used. It is primarily a protective ventilated enclosure (partial containment device) designed such that hazardous concentrations of quantities of airborne contaminants are prevented from escaping from the fume cupboard into the work room or laboratory by means of a protective air barrier between the user and the materials placed within the enclosure.

Potentially dangerous or obnoxious fumes must be efficiently conveyed from the fume cupboard enclosure to an outside discharge point where they can be safely dispersed at low concentrations. In so doing, the susceptibility to form an explosive or hazardous atmosphere inside the work space is also reduced.

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The fume cupboard is ventilated by an induced flow of air through an adjustable working opening (namely the sash) which also offers the user some degree of mechanical protection against splashes of substances and flying particles.

If anything interferes with the protective air barrier or the fume cupboard, or disrupts the air flow into and within the fume cupboard, the fume cupboards ability to protect the user may be seriously reduced.

The design and manufacture of fume cupboards is specified in the relevant British and European Standards. Further information is available from Estate Management who must be consulted on the selection and installation of new fume cupboards, to ensure that all relevant parts of the British and European Standards are complied with.

3.2 Fume Cupboard Basics

A well-designed fume cupboard, when properly installed and maintained, can offer a substantial degree of protection to the user, provided that it is used appropriately and its limitations understood.

The common parts of a fume cupboard and their major functions are as follows:

Figure 1: Basic fume cupboard

Fume Cupboard Body -- The visible part of the fume cupboard that serves to physically contain hazardous gases and vapours. The materials of construction of the cupboard body can vary considerably and will depend on the intended use of the fume cupboard.

The most common materials used are solid epoxy resin for work surface and liners, toughened glass for the sash and baffles. For special applications, stainless steel can be used where there is a high fire risk; a ceramic work surface for regular use of corrosive liquids and; polypropylene work surface and transparent PVC sash for hydrofluoric acid.

Baffles -- Panel or panels located within the fume cupboard which aid in distributing the air moving into and through the cupboard. Baffles keep the airflow uniform across the cupboard opening, thus eliminating dead spots and optimising capture efficiency. It is important that the baffles are not obstructed as this effectively blocks the exhaust path.

Sash -- The transparent screen between the user and work place that can be adjusted vertically (or less commonly horizontally). Each fume cupboard should be marked with the optimum sash height, also known as the normal sash working height. The sash should be held in this position when work involving the fume cupboard is being performed and closed completely when the fume cupboard is not in use or is left unattended. Modern fume cupboards are fitted with stops or other devices to prevent the normal sash working height being exceeded. It should be remembered that the sash provides some protection to the operator against splashing and minor explosions.

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Airfoil (or bevelled frame/sill) This is found along the bottom and side edges of the fume cupboard. Airfoils streamline airflow into the fume cupboard, reducing the creation of turbulent eddies (due to sharp edges) that can carry vapours out of the fume cupboard. The space below the bottom airfoil provides a source of room air for the fume cupboard when the sash is fully closed.

The airfoil does not form a liquid proof seal to the work surface of the fume cupboard.

Work surface -- Slab or platform which acts as the base of the fume cupboard’s workspace. Generally, it is a flat surface with a small raised edge around the periphery, known as an anti-spill lip. Sinks are often incorporated into the work surface and are positioned to the rear of the fume cupboard. The work surface may be made from plastic materials, ceramics, cast epoxy, metals etc dependent upon intended use, the older tiled type can be difficult to keep clean and do not give a truly flat base.

Exhaust plenum / extract duct work -- All ductwork and associated equipment installed between the point of connection to the fume cupboard and point of discharge. If materials such as tissues or paper towels are drawn into the plenum they can create turbulence in this part of the fume cupboard, resulting in areas of poor airflow and uneven performance.

Face -- The imaginary plane running between the bottom of the sash to the work surface. Fume cupboard face velocity is measured across this plane and is defined as the velocity of air passing through the working aperture measured in the plane of the sash.

3.3 Fume Cupboard Types

There are several different types of fume cupboard ranging from simple ‘box’ types to sophisticated ‘aerodynamic’ types. These in turn can be constant volume cupboards or variable air volume cupboards. Some modern fume cupboards may have lower air flow rates than traditional fume cupboards, (this should be no lower than 0.3 m/s in a fume cupboard specifically designed, tested and certified for this velocity). Before using a fume cupboard you should establish its type and its capabilities.

3.3.1 Constant Volume Fume Cupboards

In many older fume cupboard installations, the exhaust flow rate or quantity of air pulled through the cupboard is constant, hence the term ‘constant volume fume cupboard’. When the sash is lowered and the cross-sectional area of the cupboard opening decreases the velocity of airflow (face velocity) through the cupboard increases proportionally. By using the sash to adjust the front opening, it is possible to adjust the airflow across the fume cupboard to the point where capture of contaminants is maximized. This type of fume cupboard can be further subdivided into:

Traditional / conventional fume cupboards – these represent the original and most simple of fume cupboard design styles. With a conventional fume cupboard, the volume of air exhausted is constant, regardless of sash height. Since face velocity changes dramatically with sash position, it is particularly important when working with conventional fume cupboards to maintain the sash at its optimal height since this system will create higher air velocities as the sash opening is decreased to the point of creating turbulence at the fume cupboard face. The optimal height (usually 50 cm) should represent the point where the face velocity equals 0.5 ms-1

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Bypass fume cupboards – have an air bypass incorporated above the sash (identified by an air make-up grille) which provides an additional source of room air when the sash is closed (ie room air is able to flow into the fume cupboard by a route other than through the sash opening). As the sash is lowered, the bypass area becomes exposed, effectively ‘maintaining’ the face opening velocity and dampening face velocity fluctuations thus allowing a nearly constant total extract rate irrespective of sash position. Because variations in face velocity still occur, it remains important to utilise the optimum sash height as indicated on the fume cupboard frame.

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3.3.2 Variable Air Volume Fume Cupboards

Variable air volume (VAV) fume cupboards modulate airflow based on sash height by sensors that detect changes in air pressure or sash position. Sash height is continuously monitored and the exhaust volume adjusted so that the average face velocity is maintained within acceptable parameters. VAV fume cupboards are often equipped with a monitor that indicates whether the cupboard is in ‘standard operation’ or ‘standby operation’ mode. The monitor also has an ‘emergency purge’ button which increases airflow through the cupboard to maximum and can be used to quickly remove contaminants / releases, however this should NOT be the default setting (see Figure 2). If the alarm sound it will be for a reason and this should be reported immediately, do NOT merely mute the alarm without taking immediate action to establish the cause of the alarm.

Figure 2: Typical monitor and emergency purge control

VAV fume cupboards require technically proficient design, installation and maintenance. The primary characteristic of VAV fume cupboards is their ability to maintain a constant face velocity as sash height changes.

Some modern installations have ‘presence sensors’ which enable the control system to turn down the airflow if a person is not ‘present’ / working in the cupboard, if you have such a system you should take account of this in your risk assessment.

3.3.3 Recirculatory Fume Cupboards

In the University recirculatory fume cupboards are NOT the preferred option, particularly for work with toxic or flammable vapours or gases.

Recirculating fume cupboards rely absolutely on the absorption of the hazardous vapour or gas by a filter media, usually carbon based, before discharging the ‘cleaned air’ back into the room. When the filter media becomes saturated, as it will over time, or if it fails in anyway the hazardous material will enter the room potentially without warning!

The preferred option is always to vent fume cupboards to a safe place outside.

In the event that following a risk assessment a recirculating fume cupboard is the only reasonably practical option (it is not possible to vent to a safe place outside) to control a hazardous substance, then clearly the filter must be appropriate for the chemical you are using (or may generate) at the known or anticipated concentration, always consult the filter manufacturer as to the suitability of a particular filter medium.

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Because recirculating fume cupboards always fail to ‘danger’ they must not be used where failure would result in exposing users to an immediate acute threat to life or health. Wherever possible (available for the chemicals in use) recirculating fume cupboards should be fitted with sensors to warn of pending filter failure. In the absence of such sensors frequent filter changes are the only means of ensuring control. Since they can fail without warning and it is not possible to predict failure, if used, they must always be on a rigorous maintenance contract and be kept under constant review.

If a recirculating fume cupboard has been identified by the risk assessment as the only practicable control measure for a particular purpose, in a particular location, then any change of use or relocation must be subject to a further risk assessment of its suitability for use. It must not be assumed that a dispensation to use a recirculating fume cupboard as a control measure for a particular chemical in a particular location automatically authorises uses outside of the risk assessment for that use in that location.

3.3.4 High Efficiency Particulate Air (HEPA) Filtered Cabinets

High Efficiency Particulate Air (HEPA) Filtered Cabinets remove particulate material, but NOT gases or vapours, by passing air through a HEPA filter before discharge to a safe place outside or back into the room (recirculatory). It must be emphasised that whilst a HEPA filter is an extremely efficient way of removing solid particles as low as 2 nm in diameter they are not in themselves absorbent and do not remove hazardous or malodorous gases or vapours. If hazardous vapours or gases are used / generated in a HEPA filtered cabinet it must be vented to a safe place outside, as with any other fume cupboard. In addition if a HEPA filtered cabinet were to be considered for both capturing particulates and handling hazardous vapours and fumes it must be first established that the vapours and fumes would not have a deleterious effect on the HEPA filter itself or its seals.

Therefore recirculatory HEPA filtered cabinets, have a role in the control of small quantities of toxic powders during weighing and other non-energetic activities (for further guidance with respect to the use of HEPA filtered cabinets with powders see the University’s Nano-particle Safety Guidance HSD 147C and HSD 060C on the Safety Office website http://www.safety.admin.cam.ac.uk/.

Double HEPA filter cabinets can have the advantage of increased efficiency and potentially providing a means of changing filters whilst maintaining containment.

Remember that running a HEPA filtered cabinet when not actually in use and/or storing volatile chemicals in it may shorten the operating life of the filter as it will slowly become blocked by background ‘room dust’ in the air and could be damaged by exposure to hazardous vapours.

3.3.5 Microbiological Safety Cabinets / Laminar Flow Fume Cupboards

Although in some ways similar in appearance to fume cupboards, they have very different uses. Fume cupboards should never be used for containment of biological agents. Conversely, the majority of microbiological safety cabinets (Class 1, 2 and 3) are not suitable for handling hazardous chemicals or gases, although some are designed and installed for use with both biologically and chemically hazardous material.

Horizontal or vertical laminar flow cabinets (also called clean benches) are for specimen / sample preparation only and should never be used for handling either biologically or chemically hazardous material as the direction of airflow could blow these into the operators face.

Simple laminar flow cabinets protect the sample NOT the user.

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4 SAFE USE OF FUME CUPBOARDS

4.1 The Purpose of a Fume Cupboard

Fume cupboards are typically used to prevent or control exposure to hazardous chemicals. However, no type of fume cupboard provides total protection and even under ideal conditions some leakage will occur even with a closed sash. If exposure via leakage poses a significant health risk eg when working with substances with very low occupational exposure limits (OEL) - aka workplace exposure limits (WEL), or very high acute or chronic toxicity (eg toxins or carcinogens) then the use of total enclosure devices such as glove boxes or isolators should be employed rather than fume cupboards.

Fume cupboards are typically used to:

prevent or control exposure of laboratory workers to airborne substances hazardous to health and radioactive materials through the capture, dilution and retention of gases, vapours and (non-infectious) aerosols released within the working chamber or enclosure so they do not escape into the laboratory

dilute and discharge or otherwise remove hazardous substances so that air released to the general environment presents no significant human or environmental risk

dilute flammable gases, vapours or dusts in sufficient air to prevent or minimise the risk of fire or explosion

provide physical protection against spills, splashes and minor fires and explosions

isolate or segregate work activities for reasons of safety, product protection or cleanliness

provide secondary containment in the event of failure of the containing vessels or apparatus and so limit the potential spread of releases of hazardous materials

Fume cupboards must NOT be used:

for work with biological materials

for the disposal of chemicals

to release especially hazardous chemicals into the atmosphere

to capture contaminants generated elsewhere in the laboratory

as a store cupboard for equipment, unwanted apparatus, malodorous chemicals or chemical waste and residues

to house large items of equipment, whose bulk can cause major air disturbances within the fume cupboard body and so compromise the level of containment

4.2 Risk Assessment

Prior to any new experiment or other work being undertaken within a fume cupboard, it will be necessary to assess the potential risk posed by the intended procedure and the hazards presented through the chemicals used. This must all be considered as part of a risk assessment, but may include elements additional to chemical or biological safety. The risk assessment will identify the hazards (ie substances or conditions with the potential to cause harm) and evaluate the associated risks (ie the likelihood of that harm being realised). The assessment must consider conditions other than the normal operating ones, ie spillage, catastrophic failure of any component within the system (ie fume cupboard fan), or any other condition likely to present adverse conditions eg loss of electrical power. The assessment must define the controls that are to be in place and ensure that they are suitable and sufficient eg laboratory rules, lone working, personal protective equipment (PPE), written procedures, the use of spill trays/secondary containment, inspection regime, maintenance, cleaning, work organisation, airflow performance, competence of those undertaking the work, and level of supervision.

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4.3 How to Use a Fume Cupboard

The degree of protection to a hazardous substance offered by a fume cupboard can be rapidly reduced if the following advice is not followed. It should be noted that no fume cupboard, however well designed, can provide adequate containment unless good laboratory practices are used. Adequate planning and preparation are key. It is important that the fume cupboard limitations are recognised. It may be necessary to use special containment devices such as glove boxes or specialised fume cupboards for perchloric acid or hydrofluoric acid.

Prior to use confirm that the fume cupboard is suitable for the purpose and is operating satisfactory, ie check the on/off controls, operation of sash, audible or visible sash height alarm (where fitted) and light operation

Check the airflow gauge/indicator to see whether the fume cupboard is operating above its minimum rate of airflow. In the absence of an airflow indicator, it maybe necessary to feel air movement into the cabinet ( a simple ribbon held in front of the sah?) or to check the face velocity itself with an anemometer. A Fume Cupboard Pre-Use Operator Checklist could be utilised. An example is included in Appendix 1.

NB. The fact that a fume cupboard is switched on does not itself confirm that air is flowing through the system and at the required airflow

If the fume cupboard is not working correctly report the fault to your Departmental Safety Officer or Maintenance Section (where applicable)

Ensure that the floor area in front of the fume cupboard is unobstructed with furniture or equipment and close any windows or doors which may interfere with the performance of the fume cupboard (air currents and turbulence in the room caused by doors, windows, walls, and furniture and other obstructions placed too close to the fume cupboard could affect its performance and containment efficiency)

Do not position fans or air conditioners in the room in a manner that will direct airflow across the face of the fume cupboard as this could affect the containment of the cupboard

Ensure sufficient room inside the fume cupboard to do what is required. Remove unwanted apparatus and equipment and avoid all unnecessary clutter

Where practicable, place everything needed inside the fume cupboard before starting a procedure (this should reduce the number of arm movements into and out of the working aperture, a major cause of fume escape)

Remember most of the air entering a fume cupboard travels across the work surface and ‘up the back baffle’, see below. Therefore do NOT block the back baffle opening just above the base. If it is absolutely necessary to store material in the cupboard have a narrow shelf made that has legs allowing airflow underneath to the baffle opening.

However the air inside the body of the cupboard will circulate before eventually venting.

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Figure 3: Plan View of Fume Cupboard Showing Airflow Pattern

Maintain the protective air barrier for a safe work area by ensuring that a 150 mm wide ‘equipment free zone’ on the base is maintained behind the sash at all times

Figure 4: Formation of protective air barrier

When standing directly in front of a fume cupboard, an area of low pressure is formed in front of the user by the air passing their body to enter the cupboard. This zone of low air pressure extends into the fume cupboard for approximately 100 mm. Hazardous substances may be drawn out of the cupboard and may enter this turbulent area, which is directly in the breathing zone (see Figures 3 & 4). Convection currents caused by movement outside the cupboard enclosure and eddy currents caused by the placement of objects in the zone of low pressure may also lead to hazardous substances being drawn out of the fume cupboard

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Bad placement of materials

Good placement of materials

Best placement of materials

Figure 5: Placement of materials within fume cupboards

Avoid using large objects inside the cupboard as these may have an adverse effect on performance and block the rear slots (see Figure 5). If large equipment must be placed inside the fume cupboard, it should be raised approximately 50 mm to allow air to pass beneath the object and placed near the rear of the cupboard taking care not to block the rear slots / baffle openings, especially at the base.

Poor placement of large equipment

Good placement of large equipment

Figure 6: Placement of large objects / equipment within fume cupboards

Arrange apparatus within the cupboard to allow the operator normal access with the sash in as low a position as possible; and not greater than 0.5 m, and do not position equipment so far back that it obstructs the rear slots / baffle openings

Know the health hazards of the materials you are working with and become familiar with the signs and symptoms of overexposure

Keep the sash lowered whilst an experiment is in progress and the fume cupboard is unattended. Fume cupboards with horizontal sliding panes should be used with the sash all the way down, with as small an open area as possible

Where there is the potential for explosion additional shielding must be used

Do not put your head inside the fume cupboard enclosure at any time whilst hazardous substances are present

Avoid sitting at the cupboard as this may result in a ‘lap full’ of chemicals and it restricts mobility in an emergency

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Proper use of a fume cupboard does not negate the need for proper Personal Protective Equipment (PPE). Use suitable PPE (lab coats, gloves, goggles or face shields) at all times when working at a fume cupboard

Where possible, chemicals must not be stored in the fume cupboard and where they are, quantities must be kept to a minimum ie those in current use

All chemicals placed inside a fume cupboard must be clearly labelled

Do not leave equipment such as hotplates or stands in a fume cupboard if they are not part of the current experiment

Ensure lightweight items such as tissues, disposable gloves and filter papers are not allowed to be drawn into the fan blades as they can degrade extract performance

When highly hazardous substances are being used eg carcinogens, the fume cupboard should be appropriately labelled (an example is given in Appendix 2)

Exercise extreme caution with ignition sources inside a fume cupboard. Ignition sources such as electrical connections, variac controllers and naked flames should only be used inside the cupboard if there are no operations involving flammable or explosive vapours. If possible, ignition sources should remain outside the fume cupboard

All electrical devices should be connected outside the fume cupboard to avoid electrical arcing that can ignite a flammable or reactive chemical

Avoid sources of high heat load within the fume cupboard as these will disturb the airflow pattern and reduce the overall efficiency of containment

Clean all spillages promptly and all chemical residues from the fume cupboard enclosure after each use and keep the sash clear at all times

Plan for possible emergencies. Fires in fume cupboards should be approached with extreme caution. The use of high pressure CO2 extinguishers can result in flames being blown into the duct work.

4.4 Fume Cupboard Limitations

Used appropriately, a fume cupboard is a very effective device for the containment of hazardous materials, as well as providing some protection from splashes and minor explosions. However, the average fume cupboard does have some limitations. Examples are given below:

Airfoil sills: The majority of fume cupboards are equipped with flat or rounded sills or airfoils which direct flow or air smoothly across the work surface. Sills should not be removed or modified by the user. Objects should never be placed on these sills. Materials released from containers placed on the sills may not be adequately captured. In addition, an object placed on the sill may prevent the quick and complete closure of the sash in an emergency

Explosions: A fume cupboard is not capable of containing an explosion even when the sash is fully closed. If an explosion hazard exists, the user should provide anchored barriers, shields or enclosures of sufficient strength to deflect or contain it. Such barriers can significantly affect airflow in the fume cupboard

Horizontal sliding sashes: These should never be removed. Horizontal sash fume cupboards are designed and balanced with no more than half the face open at any time. Removal of the sashes may reduce the face velocity to below acceptable levels

Hydrofluoric acid: A conventional fume cupboard should not be used for large quantities of concentrated hydrofluoric acid. Where the work undertaken predominantly uses concentrated hydrofluoric acid, an appropriately rated dedicated

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fume cupboard equipped with a polypropylene work surface, a wash down system and transparent PVC or other suitable non-glass sash should be used

Particulates: A fume cupboard is not designed to contain high velocity releases of particulate contaminants unless the sash is fully closed

Perchloric acid: A conventional fume cupboard must not be used for heating perchloric acid. Perchloric acid vapours can settle on ductwork, resulting in the deposition of perchlorate crystals. Perchlorates have been known to detonate on contact, impact or friction causing serious injury to researchers and maintenance personnel. Specialised perchloric acid fume cupboards equipped with a wash down system must be used for such work

Pollution control: An unfiltered fume cupboard is not a pollution control device. All contaminants that are removed by the ventilating system are released directly into the atmosphere. Apparatus used in fume cupboards should be fitted with condensers, traps or scrubbers to contain and collect waste solvents or toxic vapours and dusts

Pressurised systems: Gases or vapours escaping from pressurised systems may move at sufficient velocity to escape the fume cupboard

Tubing for exhaust: Tubing is frequently used to channel exhaust to the fume cupboard from equipment located outside the fume cupboard enclosure. This is not an effective control measure

Waste disposal: A fume cupboard should not be used for waste disposal.

4.5 The Fume Cupboard as a Storage Device

Fume cupboards are designed specifically to provide ventilation for the protection of lab occupants during chemical manipulations. The airflow they provide is greatly in excess of that needed for storage of closed containers of even the most toxic of materials.

In general, the storage of chemicals within fume cupboards is strongly discouraged, unless it is for the reaction at hand. However, the realities of available space and equipment within laboratories within the University may make it difficult or completely impossible to prohibit the use of fume cupboard for storage. Where this is the case, the following is recommended:

4.5.1 Fume Cupboards Actively in Use for Experimentation

Storage of materials should be minimised or eliminated where possible as materials stored in the fume cupboard can adversely affect the containment provided. Each item placed on the work surface interferes with the directional airflow, causing turbulence and eddy currents that allow contaminants to be drawn out of the enclosure. Even with highly volatile materials, as long as a container is properly capped evaporation will not add significantly to worker exposures. It should be noted that as the fume cupboard is the focus of the most hazardous activities conducted within a laboratory, the presence of flammable or volatile, highly toxic materials can exacerbate the problems resulting from an explosion or fire within the enclosure. Even if they are not directly involved, attempts to control or extinguish a fire may result in the spilling of stored material. Unlike a fume cupboard, flammable materials storage cabinets provide additional protection in the event of a fire.

4.5.2 Fume Cupboards not in Active Use

Materials requiring ventilated storage (eg flammable and highly toxic, or malodorous substances) may be stored in a fume cupboard if they are properly segregated and the fume cupboard is labelled to prohibit its use for experimental work.

4.6 Shared Use of Fume Cupboards

Where two or more users share the same fume cupboard it is important, and a legal obligation, that they cooperate and communicate in order to ensure that their experiments are compatible and do not introduce any additional hazards in the event of a reasonably foreseeable accident / incident.

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4.7 Common Fume Cupboard Myths

Myth - When working with highly dangerous materials, the higher the face velocity the better.

Whilst it is important to have a face velocity between 0.4 – 0.6 ms-1,in most fume cupboards, velocities higher than this are actually harmful. When face velocity exceeds 0.6 ms-1 eddy currents are created which allow contaminants to be drawn out of the hood, increasing worker exposures.

Myth - The airfoil on the front of a fume cupboard is of minor importance. It can safely be removed if it interferes with my experimental apparatus.

Airfoils are critical to efficient operation of a fume cupboard. With the sash open an airfoil smoothes flow over the enclosure edges. Without an airfoil eddy currents form, causing contaminates to be drawn out of the fume cupboard. With the sash closed, the opening beneath the bottom airfoil provides for a source of exhaust air.

Myth – Using a fume cupboard makes my work safe.

A fume cupboard is only part of your safety systems – remember its limitations, and appreciate that protection is being afforded mainly by nothing more than airflow which can be relatively easily disturbed.

5 TESTING AND MAINTENANCE

A fume cupboard system will require regular examination, testing and maintenance to ensure continued safe operation. The maintenance requirement applies to the whole system, from fume cupboard to discharge stack. A planned preventative maintenance schedule must be established for each fume cupboard prior to commencing use. This will place responsibility on users, departments and Estate Management (EM). Reference should be made to the Service Level Agreement to determine departmental and EM responsibility.

5.1 Frequency of Maintenance

The COSHH Regulations require control measures used to prevent exposure to hazardous substances to be maintained in an efficient state, in efficient working order and in good repair. In addition thorough examination and tests must be carried out at least once every fourteen months. In practice this frequency of testing may be increased in accordance with the risk assessment of the effects of system failure. The schedule recommended in this guidance includes elements at both six and twelve monthly intervals (refer to Appendix 3). Where system failure would result in significantly high risk of exposure it may be appropriate to halve the indicated intervals, or supplement them with additional checks and measures. These examinations are additional to the pre-use operator checks.

Additional checks to those listed in Appendix 3 might include:

Checking filters for saturation and replace if necessary (if fitted)

If fitted, check the operation of water wash down/fume scrubber

Check the make-up air heating controls and its temperature

Remove the baffle, if fitted, and clean both the baffle and the rear of the chamber

5.2 Responsibilities

Departments, Estate Management and Contractors all have specific responsibilities for the testing and maintenance of fume cupboards. Systems should be in operation within a department to ensure air flow face velocities are tested regularly and signed records kept for a minimum period of 5 years from date of last entry (see Section 6), that Estate Management (Services Maintenance Unit) and/or an external maintenance contractor are contacted in the event of breakdown, that fume cupboards are decontaminated prior to any maintenance work being undertaken and that ‘permits-to-work’ are issued and

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completed prior to any maintenance work being undertaken. Permits-to-work should identify what measures must be taken to reduce the risks or make the area safe, what risks remain and what steps must be taken to avoid harm.

Written records of maintenance work must also be kept for a minimum of 5 years including details of all repaired and replaced components. These records should be signed and dated by those responsible for the work.

Due to the fact that maintenance activities will present those undertaking them with hazards other than those present during normal fume cupboard operations, EMBS and departmental staff must ensure that adequate precautions are taken to protect the health and safety of personnel engaged in the examination, testing, maintenance and repair of fume cupboards and others that may be affected by these procedures. This can be achieved by:

Instruction and training on recognition of hazards and assessment of risks from those hazards. There will be hazards associated with the maintenance itself (namely electricity, unguarded mechanical parts, hand tools, manual handling, access at height – from ladders and platforms) as well as those created by activities performed within the fume cupboard (namely chemicals and dust, biological agents and radioactive substances)

Undertaking a risk assessment for the maintenance work prior to any maintenance work being carried out

Devising safe systems of work which incorporate appropriate controls including competence, training, personal protective equipment and supervision. This might include implementing a permit-to-work system

Informing others that work is being carried out

Devising procedures to avoid contamination

Consideration of disposal of parts etc (eg contaminated ductwork) before work commences

Avoiding triggering fire alarms eg with smoke tracers

It may also be necessary to neutralise and decontaminate fume cupboards prior to the commencement of any maintenance work. Users are responsible for decontaminating fume cupboards. However, due to chemical contamination of fume cupboard duct systems any repair work on these installations must be progressed via Estate Management and through a ‘permit-to-work’ system.

Where maintenance work is undertaken on roofs near to fume cupboard discharge ducts, the Departmental Safety Officer and/or Chief Maintenance Engineer within a department must be contacted prior to the commencement of work in order to have the extract system stopped and/or made safe whilst the work is in progress. Due to the disruptive nature of turning off the extract system, where possible prior notice of at least 24 hours will be required and working methods must be agreed in advance.

In addition, if work on roof tops is needed to check fume cupboard ducting and plant, consideration must be given to the weather conditions. High winds, rain, snow and ice can all considerably increase the risks to those involved in the maintenance. A decision must be made by the person supervising the work as to whether the work is continued.

6 FUME CUPBOARD PERFORMANCE TESTING

Performance testing is essential to confirm that the fume cupboard is operating to a level to provide the desired fume arrest, containment and removal. It is appropriate in the following situations:

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1) Part of the commissioning of new installations

2) Part of regular thorough examination and testing to comply with COSHH Regulations

3) Following maintenance activities

6.1 Frequency of Testing

The COSHH Regulations require employers to conduct thorough examination and test of engineering control measures at least once every 14 months (annual testing is the norm). In some instances more frequent tests will be necessary. This must be determined by a risk assessment.

6.2 Record Keeping

The COSHH Regulations require suitable records of test results to be maintained for at least 5 years from the date of the last test. Appendix 4 provides an example Record Sheet.

6.3 Test Principles

6.3.1 Flow Visualisation Test

This test is a non-quantitative assessment of airflow characteristics, to examine ability of the fume cupboard to contain and remove substances.

A smoke test can be conducted by the use of a smoke pellet or a smoke-tube. The technique is to ignite a smoke pellet placed in a suitable container within the fume cupboard and note the behaviour of the smoke to assess the turbulence, clearing the base of the fume cupboard, and the efficiency of general contaminant removal without dead spots. The same observations can be made by using the smoke tubes which allow controlled release of ‘puffs’ of smoke into particular zones of the fume cupboard. The observations should be recorded and where necessary alterations within the fume cupboard can be made to improve performance. Alternatively a hand-held smoke generator (often referred to as a ‘cumulus’) can be used.

6.3.2 Face Velocity Test

This test determines the airflow (face velocity) across the sash opening. Face Velocity is measured over grid points of the maximum working aperture and a mean velocity calculated for each grid point. The mean of these area values is reported as the average face velocity. Refer to Appendix 5 for the test procedure.

The test will not demonstrate containment performance, but is a valid measure of the mechanical performance of the fume cupboard. It is a quick and easy check that can be applied during an initial fault finding exercise.

Acceptance Criteria*

Face Velocity

Recommended Range 0.5-0.8 ms-1

Optimal 0.5 ms

-1 at

0.5 m sash height

Maximum acceptable velocity 1.0 ms-1

Minimum acceptable velocity* 0.3 ms-1

Maximum deviation from mean velocity value of any other measurement within the grid

+/- 15%

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* It should be noted that in some laboratories low face velocity fume cupboards have been installed which are designed to provide safe containment at a mean air velocity below 5 ms

-1. These fume

cupboards should be labelled to this effect and checked against manufacturers specifications.

Factors to consider when assessing face velocity results The range of acceptable values is open to debate. However, the following are generally accepted principles:

i) Face Velocity too fast. Velocities greater than 0.8 ms-1are likely to generate eddy currents around users standing in front of the cupboard and these are then able to draw contaminants out through the aperture, particularly during movement by the operator

ii) Face velocity too slow. In a standard fume cupboard it is unlikely that velocities below 0.4 ms-1 are able to arrest and contain contaminants within the enclosure, particularly where external air movements due to movement of users or opening/closing of doors and windows are likely to exceed the face velocity unless the fume cupboard is designed specifically to operate at low face velocities

Where fume cupboards are found to have face velocities, which lie outside the recommended or acceptable values, for the particular design, steps must be taken to modify the system.

Subsequent testing should assess the effect on the performance of the system as a result of adjustments to the air flow rate.

6.3.3 Containment Test

The most accurate way of judging performance of fume cupboards is by assessing the ‘containment’. However, the test takes a long time and requires special equipment. The containment test is usually performed at design stage for commissioning a fume cupboard.

The test consists of releasing a material at a known rate inside the fume cupboard and measuring the presence of material just outside the sash.

There are situations when it is advisable to carry out a containment test on an installed fume cupboard. For example when smoke tests have suggested turbulent air movement within a cupboard (despite the average face velocity being acceptable) and instances of complaints of unpleasant smells emanating from a fume cupboard (despite the satisfactory face velocity measurements). In these instances a containment test is warranted.

A number of methods have been suggested to determine the efficiency with which a fume cupboard ‘contains’ a contaminant, or prevents escape of contaminant out through the sash opening. They all consist of releasing a material at a known rate inside the fume cupboard and measuring the presence of material just outside the sash opening.

The traditional method used sulphur hexafluoride gas, known to cause ozone depletion, is strictly controlled and no longer suitable for this purpose,

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References and Further Reading

British Standards Institution

BS 7258: 1994: Laboratory Fume Cupboards (BS 7258: 1994 now largely superseded) Part 1: Specifications for safety and performance Part 2: Recommendations for the exchange of information and recommendations for installation Part 3: Recommendations for selection, use and maintenance Part 4: Method for determination of the containment value of a laboratory fume cupboard.

BS EN 14175: 2003-2006: Fume Cupboards Part 1: Vocabulary Part 2: Safety and Performance Requirements Part 3: Type Test Methods Part 4: On-site Test Methods Part 5: Recommendations for Installation and Maintenance (in preparation, draft available) Part 6: Variable Air Volume Fume Cupboards

BS 7989: 2001: Specification for Recirculatory Filtration Fume Cupboards

BS 5726: 2005. Microbiological Safety Cabinets (BS 5726: 1992 now largely superseded) Part 2: Recommendations for information to be exchanged between purchaser, vendor and installer

and recommendations for installation Part 4: Recommendations for selection, use and maintenance

BS EN 12469: 2000: Biotechnology Performance Criteria for Microbiological Safety Cabinets

EN 13150: 2001: Workbenches for laboratories – Dimensions, Safety Requirements and Test Methods

Health and Safety Executive

The maintenance, examination and testing of local exhaust ventilation, HS(G)54 Second Edition; 1998; HSE Books

Control of substances hazardous to health. The Control of Substances Hazardous to Health Regulations 2002. ACOP and Guidance L5 2002

University

EM; Engineering Services Design Guide and Consultants Brief for University Buildings

EM; Design Guide and Consultants Brief for University Services and Construction Works.

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Appendix 1 - Fume Cupboard Pre-Use Operator Checklist

FUME CUPBOARD PRE-USE OPERATOR CHECKLIST (Tick to Confirm)

To be completed EACH day that the fume cupboard is used

Fume Cupboard No: Location:

Date On/Off Sash Flow Indicator

Internal Light

Fault Conditions Signed

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Appendix 2 - Fume Cupboard Label

Maintenance staff or others not directly connected with the experiments may need to know what substances are being released into the system. The following label can be used to record hazardous substances being used within a fume cupboard, contact name and internal phone number. This information can supplement the information contained on an ‘out of hours’ or ‘overnight’ card.

FUME CUPBOARD CONTENTS

FC No. Group:

Hazardous substances used (eg carcinogens):

Contact details Name:

Phone:

Important!

1. Keep this information up-dated.

2. Report all breakdowns immediately.

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Appendix 3 - Fume Cupboard Maintenance Schedule

Interval between Maintenance

Fume Cupboard Maintenance Schedule 6 Months 12 – 14 Months

Enclosure Visual examination to ensure integrity of enclosure, including seals around main panels, sinks and other services. Check storage voids underneath main aperture. *

Check operation of enclosure light. *

Replace enclosure light (ie fluorescent tube). *

Controls Activate on/off switch to confirm operation, and note operation associated warning lights.

*

Operate any other warning devices (ie sash height or low-flow switches) to confirm operation.

*

Check air-flow indicator device. In case of liquid manometer disconnect tubing and re-zero, then switch on fume cupboard and note movement of fluid column. *

Sash Repeat movement of the sash through its entire travel to confirm ease of operation (lubricate where necessary). *

Check operation of working aperture stop and over-ride mechanism. *

Check alignment of pulleys and condition of pulley wires (replace distorted or broken wire).

*

Inspect sash screen for cracks, chemical attack, or any other damage likely to adversely affect transparency of the screen. *

Ducting Examine fume cupboard-to-ductwork connection to confirm seal and physical condition.

*

Conduct visual examination of entire ductwork run for mechanical damage and leaks, including internal sections where condensate or any other concentrations are likely to cause damage.

*

Inspect mechanical volume flow control dampers to confirm freedom of movement, and absence of internal obstruction.

*

Examine fire dampers for corrosion, and operate where possible. *

Examine flow-sensing devices, or any other equipment located within the ductwork and replace if damaged.

*

Fan Check flexible coupling (including tie-clips) to ductwork for damage, wear or leakage. * Visual examination of anti-vibration mountings. *

Visual examination of all external features for mechanical integrity. * Visual examination of inside the fan casing to confirm physical integrity, absence from obstructions (ie tissues, rubber gloves, filter papers).

*

Examine electrical supply cables, switch-gear, connectors and isolators for physical damage and continued electrical operation. *

Check rigidity of exhaust stack *

Check condition and tension of drive belt, re-tighten or replace if necessary * Fit new drive belt. *

Check drive-shaft bearings for excess movement or other signs of wear. *

Re-grease bearings. *

Lubricate electrical motor in accordance with manufacturer’s recommendations. *

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Appendix 4 - Record of Examination and Test of Laboratory Fume Cupboard

1. Equipment and Location

FC Number: ………………………………………………………. Site: ………………………………

Type: ……………………………………………………………….. Building: …………………………

Manufacturer: …………………………………………………….. Room: ……………………………

Date of last examination and test: ………………………………

Date of test: ……………………………………………………….

Name of tester: ……………………………………………………

Tester’s signature: ………………………………………………..

2. Process under control Hazardous substances present

1. …………………………………………………. 1. ……………………………………………….

2. …………………………………………………. 2. ……………………………………………….

3. …………………………………………………. 3. ……………………………………………….

4. …………………………………………………. 4. ……………………………………………….

3. Conditions at time of test in service indicate contents at time of test

stood down ……………………………………………..

other ……………………………………………..

4. Permit-to-work completed and controls in place

5. Examination and test details Pass Fail N/A Comments

a) Controls i) Fan on/off ……………………..

ii) Enclosure light ……………………..

b) Flow indicators i) Fluid manometer ……………………..

ii) Electro. Mech. ……………………...

Light

Audible warning

c) Enclosure i) Sash operation ……………………...

ii) Sash height limiter ……………………...

iii) Sash height warning ……………………...

Light

Audible warning

iv) Sash transparency ……………………...

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6. Face velocity measurements

Aperture width …………… mm Aperture area …………… m2

Sash opening Height (max) …………… mm

Height (test) …………… mm

Speed setting (where applicable) High

Low

Anemometer Vane Date of calibration ……………………

Thermal

Face velocity at commissioning ……………………………ms-1

Grid Position

1 2 3 4

Reading No. (time interval)

Row A

1 (15 s)

2 (30 s)

3 (45 s)

Mean

Corrected Mean

Row B

1 (15 s)

2 (30 s)

3 (45 s)

Mean

Corrected Mean

Row C

1 (15 s)

2 (30 s)

3 (45 s)

Mean

Corrected Mean

Grand Mean ms-1

(± 15%) to

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Appendix 5 - Face Velocity Test

Although it is established that face velocity measurement will not demonstrate containment performance, the face velocity is still a valid measure of the mechanical performance of the system, and is also a quick and convenient check that can be applied during an initial fault finding exercise.

Measurements of face velocity are made in the plane of the sash opening (face), in the direction at 90° to the plane of the sash. Measurements are taken at a number of grid points evenly distributed throughout the face, giving three rows of measurements (the number of measurements in each row is determined by the width of the face). A mean velocity is calculated for each grid point. The mean of these area values is reported as the average face velocity.

1. Apparatus

a) Anemometer - with vane diameter not less than 60 mm and not exceeding 100 mm, calibrated by an accredited test laboratory

b) Support system – a laboratory retort stand and clamp or similar device to hold the anemometer vane head at the prescribed positions in the plane of the sash opening. The chosen system should cause the minimum obstruction to airflow

c) Stopwatch

d) Tape – if necessary

2. Test Conditions

a) The fume cupboard under test must be empty of equipment and clean.

b) Doors, windows and other similar openings must remain closed throughout the test. The make-up air supply, if fitted, must be operating normally. Switch on any other extraction systems in the room. All other fume cupboards in the room must also have their sash set at its maximum working aperture (500 mm).

3. Determination of the points of measurement (see Figure 6)

a) Define a rectangle such that the sides of the rectangle are 75 mm from the edges of the working aperture

b) Divide the height of the rectangle by 2 to give effectively 3 rows (row A, row B and row C)

c) Divide the width of the rectangle by a whole number n, such that the width of the cells formed does not exceed 350 mm

d) The corner of the cells define 3(n+1) grid positions at which the anemometer is held or fixed

4. Method

The procedure to measure face velocity across the sash opening is carried out as follows:

a) Set the sash at the sash stop. If there is no sash stop set the sash at 500 mm. It may be necessary to have a lower sash opening to achieve the necessary face velocity of 0.5m/sec. If so the sash and jamb must be clearly marked to show the maximum height at which this velocity can be achieved

b) Either by eye or tape divide the sash opening of the cabinet into equal rectangular areas: The grid should begin 75 mm from each edge. Divide the area into two halves (top and bottom) and then divide with vertical lines to form a grid such that the width of each zone does not exceed 350 mm (see Figure 6)

c) Position the anemometer head at the corners of each of the rectangles (NB. ensure that no part of the vane head support system lies in the airflow through the vane head and that all parts of the support system are as far as practicable from the vane head), stand well to one side (preferably behind the plane of the sash) and measure three readings using the stop

23

watch over 30 seconds such that they are taken at approximately 15 second intervals. Note the values. It is suggested that they should not vary more than ±15% from each other.

d) Determine the arithmetic means of the three readings from each of the test positions and record the value. It may be necessary to correct them using the calibration of the anemometer.

e) Determine the arithmetic mean of the 3(n+1) corrected position means and report this (grand) mean as the average face velocity.

f) Record the results in the Record of Examination. (Refer to Appendix 4)

Figure 6: Example measurement grid

Sash

Row A

Row B

Row C

Work surface

75mm

350mm

4 x 3 points, 3 measurements at each point: total of 36 measurements

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Appendix 6 - Glossary of Terms

Adequate: (In relation to a substance) having regard only to the nature of the substance and the nature and degree of exposure to substances hazardous to health

Biological agent: A micro-organism, cell-culture, or human endoparasite, whether or not genetically modified, which may cause infection, allergy, toxicity or otherwise create a hazard to human health

Control measure: A measure taken to reduce exposure to a substance hazardous to health (including the provision of systems of work and supervision, the cleaning of workplaces, premises plant and equipment, the provision and use of engineering controls and personal protective equipment)

Dust: Particles of solid material that are generated by the breakdown of solid material

Fume: Very fine particulate matter formed by the vaporisation of a solid and its condensation in air (it does not mean exhaust fumes or the fumes from acids etc)

Hazard: (In relation to a substance) is the intrinsic property of that substance which has the potential to cause harm to the health of a person; hazardous should be construed accordingly

Pre - 2005 Maximum exposure limit (MEL):

(Is the maximum concentration of airborne substance averaged over a reference period to which individuals may be exposed under any circumstances. For substances assigned an MEL, exposure must be reduced as far as is reasonably practicable below the MEL. The MEL must not be exceeded. Substances are given MELs when they give rise to serious concern about the possible health effects on workers and are commonly given to substances that are carcinogens, respiratory sensitizers and other substances that do not have a threshold level of exposure for which the health effect can be identified and in addition the hazards are serious)

Pre - 2005 Occupational exposure standard (OES):

An OES is set at a level at which, based on current scientific knowledge, there is no indication of risk to health of exposure by inhalation day after day. For substances which have been assigned an OES, exposure by inhalation must be reduced to the OES, and where the OES is exceeded, steps must be taken to reduce exposure to below the OES as soon as is reasonably practicable

Post – 2005 Workplace Exposure Limit (WEL) :

In 2005 the MEL and OEL were replaced by the Workplace Exposure Limit (WEL)

WELs are the set under COSHH as concentrations of hazardous substances in the air, averaged over a specified period of time, referred to as a time weighted average (TWA). Exposure by inhalation must be reduced as low as reasonably practicable below the WEL using the eight principles of good practice outlined in COSHH approved code of practice and guidance L5 (5

th Ed): 2005

Personal protective equipment:

All equipment (including clothing) which is intended to be worn or held by a person when using hazardous substances and which protects that person against one or more risks to their health. It also includes any addition or accessory designed to meet this objective

Risk: In relation to exposure to a substance hazardous to health, means the likelihood that the potential for harm to the health of a person will be attained under the conditions of use and exposure, and also the extent of that harm

Substance: A natural or artificial material whether in solid or liquid form or in the form of a gas or vapour (including micro-organisms)

Vapour: Gas or extremely small drops of liquid which result from the heating of a liquid or solid

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Publication History:

First published 2004

Reviewed 2007

Reviewed 2011

Revised 2016

Revised 2018: with minor changes to the guidance on recirculating fume cupboards.

Safety Office Greenwich House Madingley Road Cambridge CB3 0TX Tel: 01223 333301 Fax: 01223 330256 safety@admin.cam.ac.uk www.safety.admin.cam.ac.uk/ HSD029C (rev 4) © University of Cambridge