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Understanding arc flash

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The surface temperature of the sun is around 5,500 degrees Celsius – a little cooler than the centre of the earth. It’s hard to imagine that there is something almost four times hotter which electricians and electrical engineers could potentially encounter on a worksite.

With a blast that can be 10 times hotter than a propane torch, arc flash is one of the biggest risks facing electrical engineers. There’s no single reason it can occur and the results can be devastating.

The incredible heat generated can vaporise nearby metal components, causing explosive pressure capable of throwing someone across a room. Without the right eye protection, the flash can cause permanent blindness. Without ear protection, the volume can rupture eardrums.

Arc flash could well be responsible for a large portion of all electrocution injuries yet there is still a lot about it that isn’t understood. So what work is being done to understand and manage the risk posed by arc flash?

Assessment and protection

There are various PPE products available that are marketed specifically for their arc flash protection. The level of protection garments provide is defined by the IEC 61482 standard, which includes two different methods for certifying products: the Open Arc Test Method and the Box Test Method. The one thing the two methods have in common is they both look at how well the product will protect the wearer from second-degree burns.

The first aim would always be to remove workers from risk as far as is possible. The next stage is then to carry out a PPE assessment – the Institution of Engineering and Technology (IET) has produced some guidance around this. Essentially this will look at the incident energy level – the amount of heat that will strike an individual – that could be generated for a specific task and what level of protection would be required to guard against it.

There are other things to consider as well. Clothing material worn under the PPE – things like nylon, cotton and polypropylene – could potentially ignite and cause severe burns. In addition to the outerwear PPE, arc flash specialist manufacturers Skanwear and ProGARM produce undergarments, including underwear, that are tested to the IEC 61482 standard.

It is also important to be aware of how the garments provide protection. For example, some use a coating that can deteriorate over time with laundering.

Above: ProGARM arc flash before and after testing.

Understanding the risk

In the ORR’s 2016-17 annual report it described a “mixed picture of maturity” around Network Rail’s management of electrical risk. It praised Network Rail’s commitment to safer, faster isolations but questioned how effective the Life Saving Rules had been at improving electrical safety. The ORR said that although there was plenty of evidence of the ‘Test before earth’ rule being followed, its inspectors found that the ‘Test before touch’ rule was not followed at any of the 10 isolations it attended.

Network Rail is in the process of clarifying its PPE policy for the selection, use and management of arc flash protective clothing and is compiling a set of consistent standards that cover the myriad of different scenarios that staff and contractors can encounter when working on or near traction power equipment.

Network Rail is learning from past incidents to not only better assess what level of arc flash PPE is required but also to ensure there is clarity of understanding across the staff and contractor workforce of when the equipment must be worn.

“Provision of arc-proof clothing is of absolutely no use if it’s left in the locker or the back of a van – sometimes it’s behavioural, sometimes it’s a lack of understanding of the risks involved for particular tasks,” said James Palmer, an engineer in the power distribution team, Safety Technical & Engineering, based at Milton Keynes.

Network Rail has looked at the work carried out by the UK’s distribution network operators (DNOs) – the likes of UK Power Networks and Northern Power – in this area. “Certainly in the UK electrical industry, we’ve been in contact with some of the DNOs to understand what they’re doing,” said James.

PPE is referred to as the last line of defence. While assessing its PPE requirements, Network Rail has undertaken a large-scale analysis of common maintenance tasks and the associated risks to see if there is any way they can, and need, to be made safer. This includes looking at flameproof PPE as well as arc-proof PPE and discussing the options with the PPE committee, which James has attended a number of times.

A safety alert has been issued within Network Rail which clarified when the arc proof PPE that was issued to Network Rail Distribution staff must be worn.

The next stage is to look at things like the incident energy and arc flash boundary to model the risk and determine what level of protection is required in further different scenarios. These studies are currently being conducted by Abiodun ‘Abbey’ Oludimu, an engineer in the power systems team, Safety Technical & Engineering.

What is making the process so challenging is the variety of equipment across Network Rail’s distribution network. Standards drawn up for the 25 kV AC substation network can’t be automatically adopted for DC substations, for example.

Above all, James believes it’s important that the right PPE equipment is chosen and used where appropriate but, if the correct standard safety procedures are followed, he will be more than happy if it is never called upon.


Ultrasonic testing and electroscopic meters are two methods which can be used to detect conditions that could lead to arc flash.

Canadian company Proxxi has developed what it believes to be the world’s first wrist-worn wearable that can detect dangerous electrical conditions. The device, which is currently only available to preorder, is always on and vibrates when the wearer is getting too close to a high voltage electrical field.

Proxxi has smart connectivity which syncs the data it collects to a smart phone, logging near misses. It also has a feature which notifies a designated person if it detects that the wearer has fallen to the ground.

The wider message around arc flash is that safety systems that detect risk and protect workers are only part of the solution. Regular training and accurate assessment of the risk should mean these systems are rarely relied upon.

This article was written by Marc Johnson. 

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