School of Infection & Immunity

Electrical Safety and COSHH

The University of Glasgow has the responsibility to inform its employees of the electrical hazards that might be encountered in the workplace .

Responsibility for electrical safety is devolved through the Head of Institute to the level of individual academic members of staff in charge of laboratories and those trained within each laboratory or building to maintain (PAT test) electrical equipment. Failure to comply with legislation constitutes an offence and renders the University and the individual liable to prosecution under the Health and Safety at Work Act 1974.

Hazards Involved

Electrical apparatus in laboratories is frequently associated with other hazards such as water, corrosive, or flammable materials, potentially resulting in fire or explosion.

High levels of electrical stimulation in contact with the human body can cause the heart to go into a state of fibrillation (disorganised contractions) in which it ceases to pump blood.

Precautionary Measures

• ensure that portable appliances in use in the laboratory are in good condition.
• do not use any equipment in a manner that breaches manufacturer's instructions.
• select equipment suitable for the environment in which it is to be used
• remove as far as is possible any external hazards from the work area.
• The majority of common faults to equipment can be detected by a visual check without special equipment. Damaged equipment should be clearly labelled as soon as it is known to be unsafe and this is every user's responsibility.

As with all laboratory hazards, the four basic steps of risk assessment when working with electrical appliances should be considered.

Electrophoresis equipment and power packs

Electrophoresis is a separation method which uses electrical energy to separate molecules such as proteins or nucleic acids by their size or electrical charge. The power supplies operate at up to several thousand volts or currents of up to 500mA. This is potentially hazardous and a prominent safety warning sign should be used to indicate when the apparatus is live, even if protected by a micro-switch.

The potential for injury arises because not only are large quantities of electrical energy involved but because the supporting medium is commonly immersed in either saline or buffer.

The physiological effect of DC. currents of 10-100 mA include muscular paralysis and potentially lethal cardiac fibrillation. Such currents are within the output range of most power packs and are typical of contacts made through wet skin.

All equipment operating on less than 300 V DC is to be provided at least with the enclosing cover labelled 'Danger of Electric Shock' when in use and preferably to have the mains supply interrupted by a micro-switch or a physical interlock connected to the cover.

Equipment using more than 300 V DC MUST be protected by a micro-switch-controlled or physically interlocked cover.

To minimise danger :

• make sure mains power is OFF before handling apparatus
• handle leads with only ONE HAND and handle ONLY ONE LEAD AT A TIME. Do not touch well-earthed objects (e.g. water-taps, other electrical appliances) whilst in contact with live apparatus.
• cold-room circuits should be protected by an earth leakage circuit breaker (ELCB).

A safe system of work for electrophoresis requires that power supplies to tanks are always switched off before the lid of the tank is opened. In addition, supplementary protection by interlocking the power supply is necessary to ensure that anyone who forgets to switch off is not at risk. Effective interlocking may be provided by well shrouded sockets on the tank lid which are permanently connected to the DC supply connector and which separate from the corresponding contact pins on the tank body which are connected to the electrodes. Thus opening the tank lid automatically removes the power. There can also be power interlocking using a positive mode safety switch on a tank with a hinged lid arranged to break the AC supply to the power pack when the lid is opened. There can also be a safety interlock circuit for connection to the tank switch incorporated in the power pack itself.

Simple control circuit interlocking with a safety switch to operate a contactor or relay which breaks the AC supply to the power pack when the lid is opened is not recommended. The risk with this system is the possibility of a contactor or relay sticking in the closed position, and the indicating lamps even if provided being ignored by the operator.