7.7 Physical hazards
In any laboratory, potential hazards arise from the use of electrical equipment. The legal requirements relating to the use and maintenance of such equipment are contained in the ‘Electricity at Work Regulations 1989’ (EAW). The regulations require certain safety objectives to be achieved but do not prescribe in detail the measures to be taken. Instead, precautions should be selected appropriate to risk depending on particular work activities.
‘Portable’ electrical equipment – that is, equipment that is not part of a fixed installation and that can be connected to a fixed power supply by means of a flexible cable and plug – is by its nature particularly susceptible to damage or misuse. Examples of this type of laboratory equipment include hot-plate stirrers, pH meters, ovens, certain types of furnace, spectrophotometers, free-standing computer equipment, and so on. The condition of the plug, electrical lead and apparatus casing should be checked each time before the item is used. Any damage should be reported immediately and the equipment should be taken out of use. Most organisations carry out regular ‘portable equipment testing’ in which a thorough inspection of the equipment is carried out, including testing the earth continuity and insulation resistance.
7.7.1 Furnaces and ovens
Materials used in the construction of furnaces and ovens are heat resistant so that their electrical properties are not impaired at elevated temperatures. The gloves and tongs provided should always be used when taking samples in or out of a furnace or oven. Furnaces and ovens are designed to minimise the risk of electric shock if metal tongs are used. The main hazards from furnaces and ovens are burns; in addition, paperwork and other flammable material should be kept out of the working area. A hot crucible taken from a furnace or oven must be placed on a designated heat-resistant surface and allowed to cool before being handled. It is essential that there is plenty of room to manoeuvre when handling hot materials.
7.7.2 Compressed-gas cylinders
Gases are usually supplied to laboratories compressed in metal cylinders of various sizes. The cylinders are painted in distinctive colours to aid identification; for example, hydrogen and some other flammable gas cylinders are red in colour. However, the primary means of identification is by a label attached to the shoulder of the cylinder.
In most cases, cylinders are fitted with a regulator to reduce the gas pressure from the cylinder pressure to a suitable working pressure for the laboratory equipment. You should not attempt to obtain gas from a cylinder unless you have been instructed on how to use a regulator. Cylinders should never be moved with a regulator attached. It is recommended that regulators are tested every two years. As a precaution against the wrong regulator being connected, the cylinder outlet threads for fuel gases (for example, hydrogen and propane) have a left-handed thread, whereas oxygen and inert gases have a right-handed thread.
A laser produces an intense, highly directional beam of light, and exposure to this beam can result in damage to the eye and skin. Safe exposure limits for nearly all types of laser radiation have now been established and these are referred to as maximum permissible exposures (MPEs) by professionals in the field. However, based on experience, a more general system of laser hazard categories or classifications has been developed; basically, lasers are assigned to one of four general classes (1–4, where 4 is the highest class). The higher the class of a laser, the more stringent are the control measures required.
An He–Ne laser, for example, is a Class 2 laser. A brief description of this category of laser (taken from information published by the Laser Institute of America) is as follows:
A Class 2 laser or laser system must emit a visible laser beam. Because of its brightness, Class 2 laser light will be too dazzling to stare into for extended periods. Momentary viewing is not considered hazardous since the upper radiant power limit of this type of device is less than the MPE for momentary exposure of 0.25 second or less. Intentional extended viewing, however, is considered hazardous.
It follows from this description that you should avoid looking into a direct Class 2 laser beam and also make sure that the beam cannot be reflected by material inadvertently placed in its path. If the laser beam does enter your eye, say by an unintended reflection, you should move your head away immediately.