An arc flash is the light and heat produced from an electric arc supplied with sufficient electrical energy to cause substantial damage, harm, fire, or injury. Arc flashes can produce deafening noises, supersonic concussive-forces, super-heated shrapnel, temperatures far greater than the Sun's surface (I.e. 35,000 °F (19,400 °C)), and intense, high-energy radiation capable of vaporizing nearby materials. This can cause destruction of equipment involved, fire, and injury not only to an electrical worker but also to bystanders.
In addition to the explosive blast, called the arc blast of such a fault, destruction also arises from the intense radiant heat produced by the arc. It produces tremendous amounts of light energy from far infrared to ultraviolet. Surfaces of nearby objects, including people, absorb this energy and are instantly heated to vaporizing temperatures.
An arc flash happens when electric current flows through an air gap between conductors. Accidents caused by touching a test probe to the wrong surface or slipped tool are the most common cause of an arcing fault. Arc flashes can also be caused by:
Arc flash is caused by uncontrolled conduction of electrical current from phase to ground, phase to neutral, and/or phase to phase accompanied by ionization of the surrounding air. Because of the expansive vaporization of conductive metal, a line-to-line or line-to-ground arcing fault can escalate into a three-phase arcing fault in less than a 1/1000th of a second. The heat energy and intense light at the point of the arc is called arc flash.
As you are now no doubt aware, an Arc Flash is an extremely dangerous and life-threatening event, and is distressing not only for the individual who is the subject of it, but the families and the company involved.
Through effectively employing Fire Bear Arc Flash garments and PPE, you can lessen and potentially avoid the injuries sustained through an Arc Flash incident, however there is always an element of risk, when working in an environment where there is the potential for an Arc Flash incident.
Untreated cotton is flammable and has no flame retardant properties.
Once it ignites, it will continue to burn. The ongoing burning of cotton clothing against the skin of an individual increases the area, depth and severity of the burn received.
Therefore, untreated cotton is not a suitable fabric for base or outer garments where incident energy of above 5J/cm2(1.2cal/cm2) is possible.
However, cotton may be treated with a flame retardant chemical during manufacture, to provide flame retardant properties.
Flammable, melting synthetic fabrics (e.g. polyester) should not be worn for any electrical work. This clothing ignites easily, and, once ignited, melts into the skin, increasing the severity of the injury.
Flame retardant fabrics are generally understood to be “self extinguishing”. These fabrics may burn while exposed to a heat source, but once the heat source is removed, they cease to combust.
Examples of flame retardant fabrics include.
However, not all flame retardant fabrics meet the requirements of arc rated fabrics, as the tests for flame retardant fabrics are different to the tests for arc rated fabrics.
Therefore, base garments should be manufactured from arc flash resistant rated fabrics, not fabrics that have passed flame retardant tests only.
Flame Retardant Natural Fibres (Wool)
Testing has shown that processed wool fibres in either heavy knitwear or felted spun wool blanketing fabric exhibit good flame retardant properties when exposed to an arc event.
Arc Flash Rated (AR) Fabrics
Arc Flash resistant rated fabrics are flame retardant fabrics that have been tested and proven to self extinguish when exposed to an arc event.
Arc Flash resistant rated fabrics will specify an Arc Thermal Performance Value (ATPV) or Energy of Breakopen Threshold (Ebt) given in Joules/cm2or calories/cm2.
Protective garments for workers should provide limited arc
protection for the worker’s entire upper and lower torso, arms, and
legs.
Base Garments
Base garments are garments which are considered as outer wear but may be worn in direct contact with the skin. Base garments are worn at all times in an electrical environment.
Base Garments may take the form of either of the following:
Base garments manufactured from Arc Flash resistant rated materials should be worn where there is the possibility of exposure to incident energy of 5J/cm2 (1.2cal/cm2) or above.
The recommended minimum ATPV for base garments is 16.7J/cm2 (4cal/cm2).
For situations assessed as having a greater risk, additional garments and PPE with higher ATPV ratings may be required.
Undergarments are optional clothing worn next to the skin and under base garments.
Undergarments are not considered protective garments and are therefore not mandatory. However, if undergarments are worn, they should not exacerbate injury in the event of an arc. Therefore, undergarments should be manufactured from a minimum of 90% of natural fibres.
Wool is suitable as it presents no ignition risk. Untreated cotton, although unsuitable for base garments, is acceptable for undergarments.
Testing has shown that, although untreated cotton outer garments can ignite at energies as low as 10J/cm2 (2.4cal/cm2), close-fitting untreated cotton undergarments, worn under Arc Flash resistant rated outer clothing, present a much lower risk of ignition.
Flammable, melting synthetic undergarments present a high risk of ignition and will add to injury by burn, melt and drip, and therefore should not be worn.
Thermal outer garments are garments worn over base garments to provide thermal protection against low ambient temperatures e.g. Jackets and Pullovers.
It is not essential that these garments be Arc Flash resistant rated, however they should have an outer layer that is flame retardant in accordance ISO 14116, and have no flammable melting synthetic layers or components. Alternatively, the use of heavy woollen knitwear or felted spun wool blanketing fabric is also recommended.
Any garment which is not Arc Flash resistant rated should not be relied upon to provide additional or increased arc protection.
Where higher levels of arc protection are required, this may be achieved by the use of Arc Flash resistant rated outer garments worn over base garments, such as:
When considering the use of multi-layering of Arc Flash resistant rated garments, information should be obtained from the manufacturer to determine the effective combination of layers where possible.
It should be noted, that when working in high temperature conditions, heavy weight clothing or multiple layers should only be worn for the duration of the task, so that the risk of heat-stress is reduced.
When the use of the arc-rated clothing and associated arc rated PPE introduces additional hazards to the worker, the safe work plan shall be reviewed and revised as appropriate to ensure that the overall hazard to the worker is reduced to as low as reasonably practicable.
Rainwear is designed to be worn over base garments. Rainwear should either be flame retardant in accordance with ISO 14116, or should be Arc Flash resistant rated in accordance with ASTM F 1891 or equivalent. Any rainwear garment which is not Arc Flash resistant rated should not be relied upon to provide additional or increased arc protection. Rainwear should not be treated with additional products other than those specified by the manufacturer.
Care & Maintenance of Arc Flash resistant rated clothing Arc-rated clothing should be cleaned and maintained in accordance with the manufacturer’s recommendations. The end user should regularly inspect and maintain the clothing and equipment to protect the integrity of the arc rating.
Damaged, deteriorated or faded clothing should be
replaced. If minor repairs to small tears and holes are made in
arc-rated clothing the repairs should utilise the same materials as the
original garment. All stitching should utilise an inherently flame
retardant thread or the equivalent to that used in the original garment.
Insulating gloves (sometimes referred to as Voltage Rated gloves) are used to provide protection for workers from the risk of electric shock. To provide protection from the thermal effects of an arc, insulating gloves should be worn in conjunction with approved protective outer gloves.
Insulating gloves shall be selected, used and maintained in accordance with one of the following Standards - AS 2225, IEC60903, or ASTM D120 / F496, as appropriate.
Approved protective outer gloves should be specified by the manufacturer of the insulating gloves. These outer protective gloves should be worn over insulating gloves to provide protection from the thermal effects of an arc as well as other mechanical hazards.
The design of the outer gloves should prevent the glove tightening onto the hand in the event of an arc exposure, so as to allow for easy removal of the gloves. This may be achieved by utilising sacrificial stitching along the fingers.
Inner gloves are thin fabric gloves worn under insulating gloves to absorb perspiration. These gloves also provide additional thermal protection in the event of exposure to an arc. Inner gloves with flame retardant properties are available.
Arc Flash resistant rated gloves may be used for situations where there is the possibility of exposure to incident energy above 5J/cm2 (1.2cal/cm2), but where insulating gloves are not required.
The Standard IEC 60903 recognises “composite gloves”. These are insulating gloves that do not require protective outer gloves for mechanical or arc protection. They have both an electrical and an arc rating.
Note: The
storage temperature requirements of some of these composite gloves may
not be compatible with Australian climatic conditions.
Safety glasses (or alternatively, face shields) should be worn at all times where there is the possibility of exposure to incident energy above 5J/cm2 (1.2cal/cm2). They should comply with the requirements of AS/NZS 1337.1 or AS/NZS 1337.6, be manufactured with a medium impact resistance, have a non-conductive frame, a wrap around design or be fitted with side shields. Safety Glasses may be worn under face shields or hoods.
Arc rated goggles are designed to be used in conjunction with Arc Flash resistant rated balaclavas. The goggle and balaclava combination may be worn in place of an Arc Flash resistant rated hood. Care should be taken to ensure that there is no gap between the two components. Arc Flash resistant rated goggles should be approved under ANSI Z87.1.
Australian utility injury statistics show that the most commonly burnt part of the body, in an electric arc event, is the face. Arc Flash resistant rated face shields (with a chin cup or shroud) can provide effective protection for the face in these situations.
Arc Flash resistant rated face shields should be considered where there is the possibility of exposure to an incident energy / heat flux above 5J/cm2 (1.2 cal/cm2).
To reduce the risk of inhalation burns by the entry of hot hazardous gases under the face shield, the face shield should include some form of chin cup or shroud. (Either a rigid plastic chin cup or flexible Arc Flash resistant rated fabric shroud).
Arc Flash resistant rated face shields without chin cups/shrouds are not recommended. Arc Flash resistant rated face shields should be approved under ANSI Z87.1.
Safety
helmets should comply with AS/NZS 1801 and be selected and used in
accordance with AS/NZS 1800. Helmets should be Type 1 construction and
comply with clause 4.4 of AS/NZS 1801.
Arc Flash resistant rated balaclavas are designed for use with Arc Flash resistant rated goggles or face shields, to provide additional protection to the neck and head.
An Arc
Flash resistant rated hood is a beekeeper-style hood fitted with an Arc
Flash resistant rated face shield and designed for use with a safety
helmet. These hoods may be worn in conjunction with switching
coats/jackets and offer a high level of protection to the face, neck,
head and airways.
Appropriate footwear shall be selected, used and maintained in accordance with AS/NZS 2210.1 for all work where there is a potential for exposure to electrical hazards. Full leather uppers are recommended for arc environments. Leather derivatives such as nubuck or suede are also acceptable.
Other materials, such as moulded rubber may be acceptable, depending on the risk. Woven nylons or other synthetic uppers are not recommended.
It
should be noted that footwear marked as being suitable for use in
electrical hazards does not provide any additional protection from
electric arc events.
Whilst PPE is a vital step in protecting employees against arc flashes, equipment is often left unprotected. Arc flash relays can detect the arc and send a trip command to the circuit breaker. The ultra-fast tripping will reduce the amount of damage caused to the switchgear, reducing your equipment’s downtime.
