Along with my Premium Power colleague, Senior Electrical Engineer Andrew Hogan, I was a guest of DuPont’s Elaina Harvey (UK) and Jean-Claude Duart at their European Technical Centre in Geneva for two days in early April. The purpose of our visit was to learn more about DuPont’s innovations particularly as regards its inherently flame resistant meta-aramid fibre NOMEX®™ which is used in many arc rated garments, and to witness at firsthand how the NOMEX®TM materials performed under arc testing. I have to say in my capacity as a risk assessor and occasional user of arc rated PPE that I was suitably impressed and reassured by what I saw and learned as regards protection against burn injury.
Potentially fatal consequences of arcing were very evident!
Specialising in arc flash hazard analyses, and the assessment of risks associated with work on or near live electrical equipment, we in Premium Power have known fully the dangers of arcing for some years now. We read the reports of court prosecutions both here in Ireland and in the UK, and are increasingly hearing anecdotal accounts of less serious accidents. We also know that published accident statistics are not necessarily good indicators of risk. And yet it was very powerful to witness the impact of arcing during fabric and garment testing at DuPont’s test facility. The DuPont TM Arc-Man® TM tests certainly left a lasting impression. Arc-Man®TM determines the arc rating of flame resistant materials for clothing and overall garment response under defined arcing conditions in accordance with the IEC I.S./B.S. EN 61482-1-1:2009 test methods. In other words, ArcMan® replicates pre-determined prospective arc accident conditions.
We were present for three tests. Two of those involved exposure of arc rated materials and garments to arc incident energy of 11 calories/cm². Perhaps the biggest impression formed was that arcs which sustained merely 200-300 milliseconds, both generated not only flashes of intense heat and light, but also resulted in very loud bangs and clouds of smoke (metal conductors melted by the arcs) even in the open air, and which I can only describe as being a little startling. This, despite the fact that we observed from a safe distance, had forewarning and wore darkened-glass protective goggles. We stood outside in the open air, and some 18 metres away from the arc (Arc-Man® TM test rig) during the tests. I can only imagine the distress, not to mention possible internal injury, that an exposed worker would’ve suffered even though s/he, and not the mannequin, had been wearing the arc rated clothing. The tests confirmed that a worker clad in the garments under test would have been spared serious burn injury. However, the wearer would not have been protected from any other trauma, physical or psychological, arising from the toxic, thermo-acoustic explosions. I shudder to contemplate the severity of burn injury to an unprotected worker exposed to a similar flashover. We also observed a 30 calorie/cm² test which, needless to say, necessitated our wearing ear plugs, even at a distance of 18 metres from the blast!
Legal duty to ‘prevent risk’ of injury, and not merely to protect worker exposed to a flashover
The DuPont Arc-Man®TM tests serve to remind us of the employer‘s legal duty to prevent, so far as reasonably practicable, risk of injury from arcing to any person who uses electrical equipment and installations, or who may otherwise be affected. ‘Use’ includes not only operation, but also activities such as commissioning, testing and maintenance. Towards this end, the employer must identify all foreseeable arc hazards, assess the risks, and put in place the necessary preventive and protective measures. In this regard, the duty is to prioritise prevention in all cases where avoidance is either not possible or is otherwise impracticable.
Of course, one can only assess arc risks if one knows the prospective arc incident energy levels along ones electrical network. This requires a network survey, followed by network modelling and prospective arc incident energy calculation in accordance with the IEEE 1584 Guide for Performing Arc Flash Hazard Calculations using sophisticated software. There are of course other dimensions to arc flash risk assessment, namely hazard identification, hazard analysis, assessment of potential injury and determination of preventive and protective measures. Suitably selected and used, arc rated PPE will undoubtedly be an essential safeguard in many situations, but as already alluded to, must only be deployed as ‘a last line of defence’.
Arc flash is a multi-faceted and complex hazard
The term ‘arc flash hazard’ may be somewhat misleading to the unitiated. Arc flash is not a single hazard, as the term would appear to imply, but is instead a multi-faceted and complex phenomenon. It includes many situations, sources or acts involving live electrical equipment and installations, in which exists potential for arcing. In other words, work on or near live electrical equipment presents many arc flash hazards, not all of which are obvious. This poses the question to every employer, and health and safety practitioner alike, ‘Now that I am in possession of my prospective arc incident energy levels, does my organisation possess the necessary competence to make an adequate assessment of the risks to which my people are exposed?’ One must be careful not to overestimate the organisation’s competence.
Pat MacNally is a Risk Assessor and Compliance Engineer at Premium Power. Premium Power specialise in arc flash mitigation.
DuPont™, Arc-Man® and NOMEX® are registered trademarks or trademarks of E.I. du Pont de Nemours and Company or its affiliates.