Minimising the Risks of Arc Flash
Author: Simon Raglione-Hall
Technical Manager – Clydesdale Ltd
According to research carried out by ISSA, electrical arc flash events occur at least daily in the UK, the results of which can be disastrous, possibly fatal. While industry is increasingly aware of the risk and the need for reducing its effects, many electrical workers are still unaware that they are regularly exposed to potential electric arcs at life-threatening levels.
The key elements to an arc flash risk assessment (as required by EU law) are:
1. The initial investigation and company education.
A company and its employees need to understand the arc flash risks they face. Initial investigation involves identifying all live electrical work – however insignificant it may seem – finding the voltage and current, the distance to workers at risk and the characteristics of electrical supply. Risks can then be quantified into potential incident energy. Several tools such as Clydesdale’s heat flux calculator are available to aid this process. Calculation guidance is also given and continually updated in IEEE 1584 to ensure best international practice. Traditionally, this energy is expressed in calories per square centimetre (cal/cm2) with a recent move towards Joules.
Andy Calderwood from Clydesdale Limited says; “People are surprised by the relative level of their risks. The perception before assessment is usually that their high voltage work carries the risk of arc flash and that day-to-day, low voltage tasks are risk-free. After assessment they are often stunned that work they carried out without concern was actually among the higher risks”.
2. Risk reduction
Tasks and associated incident energies should be reviewed to reduce them to minimal levels. The best sort of arc flash protection is to remove the risk altogether by not working live. Possible areas of risk reduction can be by replacing high-risk electrical installations, implementing arc flash detection and control, re-formatting electrical supplies to lower potential incident energy and distancing workers from potential arc sources.
Again, Andy of Clydesdale says; “A customer operating offshore drilling platforms carried out flash risk assessment and found some very serious arc risks. They successfully reduced all current and future risks to sub 8 cal/cm2 levels.
3. Protective equipment
Residual risks to workers can be further reduced by Remote Operation Devices (ROD) and by Personal Protective Equipment (PPE).
Many types of switchgear that need human operation could be operated by Clydesdale’s ROD kit allowing simple mechanical operation from several metres’ distance.
To help ensure that any PPE purchased is the correct type, a guide to its selection is given below.
Andy Calderwood’s advice; “We don’t want someone to carry out initial arc flash assessment and then just place their guys in suitably rated PPE. We can supply clothing up to 100 cal/cm2 rating but the risks to workers from an arc that big are more physical than thermal. In the USA, NFPA 70E basically tells you not to work with risks greater than 40 cal/cm2.”
Once policies and procedures are in place they should be recorded, clearly documented and communicated to those at risk. Guidance on what workers can and can’t do and why, should always be given. The better the education and information, the more lives could be saved.
The most readily available and commonly known source of arc flash protection is clothing. However it should only be specified once all arc risks have been assessed and reduced to their lowest practical level.
Protection should be to body and limbs but with special care to protect hands and face. Hands are typically the parts closest to an arc and are exposed to the highest energy. Face and head are the most easily injured but the hardest to heal.
Arc flash clothing is most easily specified using its Arc Thermal Performance Value or ATPV, given in cal/cm2. The basic requirement is to ensure a garment’s ATPV is higher than the incident energy identified in arc flash assessment. Testing of PPE garments to determine ATPV, is covered by EN 61482-1-1 in Europe and is carried out using an ‘open’ or unconstrained arc between 2 electrodes.
An alternative method is the garment ‘Class’ system covered by the EN 61482-1-2using a ‘box’ arc directed at a garment to simulate a fault in a cabinet or enclosure. Test results are quite coarse but give either Class 1 or 2. Class 1 is very basic level protection whereas Class 2 is relatively high.
Amazingly, there are no European standards available for arc flash testing gloves and face protection for both ATPV and Class. It’s being addressed but for now, manufacturers must ensure their products demonstrate required protection using above tests or derivatives.
Further consideration should also be given to wearability particularly when using garments based on artificial fibres which don’t breathe as well as those based on natural fibres. A manufacturer’s ability to support the technical aspects of the entire arc flash process is also pivotal to a successful implementation.
Finally, arc flash PPE garments or equipment should be produced in accordance with EU PPE Directives. Arc flash PPE is ‘Category 3’, meaning its failure could be fatal. Therefore products must be tested and assessed by external, ‘Notified’ bodies to ensure correct construction.