Within the field of industrial safety, most employers are aware of and understand the importance of their workers wearing hard hats, protective gloves, and safety boots whilst on the job.
However, there is not the same understanding where the risk of being exposed to an arc flash is involved. This is despite the fact that an electrical explosion is actually much more common that what we are led to believe.
There are actually a number of different things that can cause an arc flash to happen, including equipment not being sufficiently rated for the available short circuit current or accidental contact, to corrosion of equipment or deterioration or contamination – making the risk of an electrical explosion much more prominent than what is widely believed.
Where an arc flash occurs, it can have devastating consequences for anyone exposed to one. This is because they expel huge amounts of deadly energy, with temperatures reaching as high as 20,000 degrees Celsius – hotter than the surface of the sun!
Arc Flash Calculations
Performing arc flash calculations can be a challenge for even the most experienced electrical technicians. To help with this task, the Institute of Electrical and Electronic Engineers (IEEE) published a ‘Guide for Performing Arc Flash Hazard Calculations’. It comprises detailed methods and data that are useful for calculating arc flash hazards for both simple and complex electrical systems.
The steps that are necessary to properly perform an arc flash calculation include collecting the system and installation data, determining the system modes of operation, determining the bolted fault currents, determining the arc fault currents, finding the protective device characteristics and the duration of the arcs, documenting the system voltages and classes of equipment, selecting the working distances, determining the incident energy for all equipment, and finally, determining the flash protection boundary for all equipment.
Arc Flash Risk Assessments
The main concept for safety from an arc flash assessment is that workers can be assumed to be safe if the personal protective equipment (PPE) and clothing that they are wearing has a greater arc rating than the energy that they could be potentially exposed to as a result of an electrical explosion.
So that your workers are wearing the appropriate level of arc rated clothing and PPE, an employer must first carry out a full risk assessment. By doing this they will be able to ascertain what the arc incident energy is likely to be in the event of an arc flash. It is the responsibility of the employer to perform these risk assessments that are specific for each and every installation and working conditions.
When assessing the risks from an arc flash, there are a number of quantitative parameters that must be measured, including the number of conductors, arc duration, supply voltage arc current, and the number of phases electrode gap environment: ‘arc in box’ or ‘open arc’ distance between arc and surface of clothing and PPE worn by workers.
From the above parameters an employer can establish if their workers need to be wearing Category 1 or Category 2 layered Arc Flash Protective clothing and ppe.