The equipment considered in this Risk Assessment includes laboratory ovens, Bunsen burners, heating plates and mantles, steam oil and sand baths and hot air guns i.e. temperatures up to 800°C. The use of very high temperatures, furnaces, experimental rigs etc. must be covered by a separate Risk Assessment.
- Personal injury and burns from hot surfaces, liquids, vapours or flames.
- Sources of ignition both from hot surfaces, liquids or flames and from electrical components.
Risks and who is likely to be injured?
- Contact burns are likely and may range from trivial to severe but most likely will affect only the user.
- Ignition or explosion is much less likely but may result in widespread injury to others.
Many heating appliances contain electrical elements (see the separate Risk Assessment "Use of Standard Electrical Equipment"). If any heating device becomes so worn or damaged that the heating element is exposed, the device should immediately be taken out of service.
All heating devices (apart from steam baths) must be kept well away from flammable material.
- With the exception of vacuum drying ovens, laboratory ovens rarely have any means of preventing the discharge of material volatilised within them. Thus it should be assumed that these substances will escape into the laboratory atmosphere but may also be present in sufficient concentration to form explosive mixtures within the oven itself. This hazard may be reduced by venting the oven to an exhaust system.
- Ovens should not be used to dry any chemical sample that has even moderate volatility and might pose a hazard because of acute or chronic toxicity unless the oven is constantly vented to a safe exhaust.
- Glassware rinsed in solvent poses a danger of explosion if dried in an un-vented oven.
- Bunsen burners are used less and less in laboratories. The naked flame is liable to set off the fire alarm system if set in the line of sight of a flame detector. If used, care must be taken to shield the flame from the detector.
- The naked flame is a particularly hazardous ignition source and must never be used near open containers of flammable liquid or in environments where appreciable concentrations of flammable vapour may be present.
- A Bunsen flame may be difficult to see in bright sunlight. Blinds should be drawn to shade the flame.
Hot Plates, Heating Mantles
The state of the heating element should be checked. If the covering is broken or worn the equipment must not be used. If water or other liquid has been spilled onto the element, the equipment must be electrically checked before use.
Steam, Oil and Sand Baths
- Extreme care must be taken to mount the baths in such a way that they cannot be overturned or that water cannot fall into an oil or sand bath causing hazardous splattering. For oil baths, secondary containment must be used to restrain any possible spills.
- Oil expands in volume when heated:- overfilling should be avoided.
- Material heated in such a bath should be mounted in such a way that it can be quickly and easily removed from the bath in an emergency.
- Oil must not be overheated so that it smokes or decomposes or is in danger of ignition.
- Proper labelling should identify the oil and its safe working temperature.
- Attention should be paid to the following:-
- the size and location of the bath,
- operating temperature and temperature control devices,
- the type of oil used,
- available ventilation,
- the method of cooling hot oil,
- storage of oil for reuse,
- proximity of water or chemicals.
- Steam baths present a danger of scalding from hot steam and care must be taken especially when mounting or removing reaction vessels.
- In all cases, when using such apparatus, proper protective equipment must be worn i.e. lab. coat, safety glasses and gloves.
Hot Air Guns
- Laboratory hot air guns contain an electrically heated element that typically glows red hot. Also, the on-off switches and motors are rarely spark free. For these reasons, hot air guns present as serious an ignition hazard as a naked flame and must never be used near open containers of flammable liquid or in environments where appreciable concentrations of flammable vapour may be present e.g. over glassware rinsed in solvent.
- The air emerging from a heat gun is very hot indeed and is invisible and so the front end should be treated with all the respect due to a blow torch.
The use of some of these heating devices i.e. steam baths, Bunsen burners, hot plates and heating mantles is part of Undergraduate training. In the remaining cases, training should be given by a competent person.
Level of Risk Remaining
With the proper training, the level of risk is low although constant vigilance is necessary to avoid injury and possibly serious burns.