My first arc flash experience was many years ago as a first- year tradesperson when testing using test lamps. Test lamps are a thing of the past and they had large test probes. I was
testing with these large probes on exposed terminals that were too close together and ‘bang’.
I was extremely lucky as I was testing very close to the transformer and so the fault level was ‘huge’ – the HRC fuse ‘blew’ and prevented more significant consequences. The test lamp probes were ‘fried’ and some of the customer’s switchboard components sustained unrepairable damage. I received no injuries at all thanks to the HRC fuse – many others are not so lucky.
RESULTS OF AN INCIDENT
There was an additional cost for the company I was working for in replacement parts, some lost time and my reputation was somewhat damaged. The good news was that I never did anything like that again. Learning from one’s mistakes is always a good idea or better still, learn from training.
Arc flash incidents can not only result in death or serious burns but also downtime for the business, loss of reputation for the business and individuals, and therefore damage to branding, significant stress and grief for all concerned including family and friends, legal defence fees, increased workers compensation premiums, loss of licences, loss of the business and livelihood, and in some cases and personal and company fines and/or imprisonment if prosecuted by the safety regulator.
Arc flash incidents generate plasma, the fourth state of matter
– super heated and ionic gas to approximately 5,000 °C. Plasma cutters use this fact to cut steel and so arc flash plasma will cause terrible injuries to the human body. There is also an intense blinding light, a deafening bang likened to the noise from a jet engine or a stick of dynamite going ‘off’, a significant pressure wave, metal vapour and toxic gases are given off, and shrapnel and molten metal droplets thrown at the person. The temperature at the arc tips can reach 20,000 °C but it is typically the plasma that will cause the severe injuries. Arc flash incidents in enclosure may ‘blast’ the plasma cloud at the person like a blast from a cannon.
The first most important thing to learn about arc flash incidents, is that cotton clothing is flammable and once on fire, may cause terrible burn injuries in excess of what would have otherwise occurred.
Electrical workers need to get out of cotton clothing and into arc resistant clothing. This can mean the difference between going home at the end of the day and not going home at all.
FABRICS AND CLOTHING DESIGN
There are various brands and types of fabric. There are treated or inherent fabrics. Treated generally means that cotton has been treated to make if ‘flame retardant’. Inherent means that the fabric
is made of material that is naturally flame retardant and/or arc resistant. All arc rated clothing is flame-retardant but not all flame- retardant clothing is arc rated. We are looking for a fabric that has an Arc Thermal Performance Value (ATPV).
There are four categories of arc resistant clothing – 1 to 4. Categories 1 and/or 2 clothing are for smaller incident energy levels and can be used as ‘everyday’ clothing for electrical workers and Categories 3 and 4 clothing are for higher incident energy levels and are often called bomb suits.
Clothes need to be user friendly and so need to be able to ‘breath’ and not cause welts or overly restrict body movement.
There are woven or knitted fabrics with knitted least preferred as knitted fabrics can come ‘undone’ if snagged.
How the arc flash clothing is ‘put together’ can make a huge difference to its performance in an arc flash event e.g. button’s may pop off and the shirt will then gape open even if arc resistant thread has been used for the button. This will expose the person’s chest to the arc flash energy.
Energy Networks Association’s document NENS09 National Guideline for the Selection, Use and Maintenance of PPE for Electrical Arcs Hazards, details how clothing for the electrical industry should be constructed. This includes having long sleeved shirts with fully gusseted sleeves to prevent roll up, no exposed buttons, studs or zippers i.e. they are covered with a placket of the shirt material, ½ closed front with buttons or clips to the neck (behind the placket), and pockets with a flap to stop molten metal dropping into the pocket.
Some flame-retardant clothing with an ATPV now have no restrictions on the number of washes with the manufacturer quoting “Won’t Wash Out, Won’t Wear Out”.
IMPLEMENTING ARC FLASH CLOTHING
Implementing arc flash clothing is best achieved in consultation with staff. Some organisations have found that productivity has even increased through this process as staff feel valued. Organisational culture is often improved through such initiatives.
‘Wear trials’ are strongly recommended with a select number of employees and fabrics.
There are some light weight and user-friendly fabrics now available.
OTHER ARC RATED PPE
Boots made with leather uppers are generally regarded as arc rated. Helmets to AS/NZS1801 should suffice. Insulated gloves with leather outers or arc rated insulated gloves should be used.
Face shields should have an ATPV for the incident energy at the location and need to include a chin cup to prevent the plasma getting up behind the shield and burning the face and neck.
Under garments should be arc rated. Outer garments such as raincoats also need to be arc rated. Pure wool outer jackets should be OK as wool is not flammable.
WHAT NOT TO WEAR
Various items should not be worn when working with electricity. These include exposed jewellery, exposed under garments that are not arc rated, short sleeve shirts or sleeves rolled up, metal fasteners such as metal zippers or buttons, synthetics over arc rated clothing, ordinary face shields, or any items without an ATPV rating.
Cat 3 or 4 ‘bomb’ suits cause sensory deprivation and will restrict movement. They can cause dehydration and overheating on hot days. There are brands/makes of bomb suits with inbuilt cooling fans to help minimise this issue. Designing out the arc flash issue will be best but ‘bomb’ suits are likely to be needed for some tasks on some equipment.
Arc flash incidents can result in terrible injuries or death. Arc rated PPE is the last line of defence but can mean the difference between going home or not.
Cotton clothing is flammable and should no longer be used by electrical workers. Tee shirts and shorts are totally in appropriate for any electrical worker.
I liken arc flash clothing to using a seat belt in a car. I have never needed a seat belt or arc flash clothing but if I have a car accident or arc flash incident, then I will be awfully glad I wore the seat belt or arc flash clothing.Implementing arc flash PPE, particularly clothing, with staff consultation through ‘wear’ trials is likely result in staff ‘buy-in’ instead of dictating what arc rated clothing will be worn.
To discuss this matter further or to organise arc flash training contact: Chris Halliday – firstname.lastname@example.org