Arc Flash Protection

The number of injuries caused either directly or indirectly by electricity remains, thankfully, very low in comparison with other forms of injury. Perhaps this is due to the perception that electricity, when not given due respect, can be dangerous, even life-threatening. However, there have been several reported instances this year of workers receiving injuries whilst working with electricity. The most notable being the fining of two firms by the HSE when workers received life-changing burns from an electrical flashover incident whilst working on a live distribution board. The subject of live working is one which crops up fairly regularly at SELECT electrotechnical meetings and it is perhaps timely to clarify the regulations governing such work.

Before looking at the legalities of live working, its worth considering the level of energy that can be released during an arc flash event.Typically, an 11kV system is capable of generating 200 to 250mVA for up to five seconds or more in the event of a fault. This can create an arc of radius 300mm with a temperature of 20,000oC. The temperature rise after 0.1s at 1m from the arc is 1,526oC. That rate of temperature rise is faster than any human can respond and potentially life-threatening. Of course, if the circuit is dead then this cannot happen.

The legal framework in place to protect workers starts with the Health & Safety at Work etc Act 1974. This is the principle law defining employers and employees duties for providing safe systems of work, competent employees and cooperation between employees and employers to ensure their respective duties are met. For those working in the electrotechnical industry, the Electricity At Work Regulations (EAWR) 1989 and the Personal Protective Equipment (PPE) at Work Regulations 1992 are just two of the range of regulations that define the way to remain safe while working.

Regulation 14 of the EAWR 1989 states that:

No person shall be engaged in any work activity on or so near any live conductor* that danger may arise unless:-

a)It is unreasonable in all the circumstances for it to be dead, and

b)It is reasonable in all the circumstances for him to be at work on or near it whilst it is live, and

c)Suitable precautions (including where necessary the provision of suitable protective equipment) are taken to prevent injury.

(*other than one covered with insulating material so as to prevent danger).

The dutyholder, when faced with Regulation 14, must consider what means he/she has at his/her disposal to achieve safety. This consideration will undoubtedly start with a risk assessment of the work to be undertaken. A risk assessment for such work is a legal requirement and should follow the HSE guidelines of:

1.Identifying the hazards

2.Identifying who might be harmed and how

3.Evaluating the risks and deciding on precautions

4.Recording the significant findings

5.Reviewing and revising as necessary

To many, it is never unreasonable in all the circumstances for an electrical circuit to be dead prior to commencing work; however, many dutyholders are faced with the challenge of creating a safe environment for their workers against the pressure from building users to avoid disruption of their work environment. This may lead the dutyholder to consider the use of flame retardant PPE at an early stage of the risk assessment. When considering the effects of an arc flash incident there is a range of flame retardant PPE available for dutyholders to specify. However, there are several issues associated with its use which must form part of the risk assessment process, such as: ergonomics, the users sensory deprivation, continuing integrity of the PPE as work progresses and other injury mechanisms such as loss of hearing and sight. Ken Morton, HM Principal Electrical Inspector at the HSE puts the case for working dead quite succinctly when he points out that no piece of electrical switchgear has ever been designed with the use of a thick leather gauntlet in mind.

The reasonableness of live working will no doubt continue to be discussed for the foreseeable future. However, after considering the legal framework in place and the difficulties of working with flame retardant PPE, the only conclusions that can be drawn from this issue are:

1.Dutyholders must comply with the legal requirements and, using a risk assessment process, seek to eliminate or control the hazard prior to the use of PPE.

2.Flame retardant PPE has its uses BUT as a means of protecting persons from the effects of an arc flash incident its use is only acceptable as a last resort.