Safety in a Flash

The word “flash” seems very simple and even light to describe such a dramatic event which can cause so much harm. Its larger brother, “arc blast” is much more descriptive really.

For those of us that work in the electrical generating industry, the terms are familiar and are often part of a structured formal policy and procedural framework that encompasses strict training and competency checks. To the layperson they might be never heard.

As many of us know, OHS professionals often have pet subjects, or ones that send a little shiver down their spine. My personal ones are housekeeping and electricity. The former leans happily into my belief that a clean and tidy workplace is not only safer but can be more efficient. One of our many examples of common goals with our goal orientated executive colleagues. The other, gives me pause at all times. If I can’t see it, smell it or hear it, then I am naturally built to consider it with caution.

What is arc flash?

Now we should spend a little time to define what exactly an arc flash is.

The Institute of Electrical and Electronics Engineers (IEEE) define the event as “an electric current that is passed through the air when insulation or isolation between electrified conductors is not sufficient to withstand the applied voltage.”

As I mentioned above, this definition hardly describes the intense light and heat, pressure wave, and thermal shock produced.

In fact, it is an explosion which involves electrical arcing. Normally at temperatures reaching several thousand degrees Celsius and the pressure wave associated with that explosion. Although it occurs within a blink of an eye, the damage to the human body can be severe, such as burns, damage to hearing and to vision.

Like all explosions, the debris that it propels can also cause major injury as they are propelled from the epicentre outward. It goes without saying that such explosions can be life changing for any employee caught in the wave of destruction.

Now, I am sure it has crossed your mind that people surely work on de-energised systems, so how can arc flashes occur?

De-energisation

It is, of course, the first tenant of working in the electrical industry, enshrined in many countries and industries by regulations and standard practices. However, we cannot forget that a person often has to carry out this de-energisation exercise. This involves placing equipment in what we call an “electrically safe work condition”, which involves taking an electrical conductor or circuit part being disconnected from energised parts, locked and tagged, and then tested to ensure the absence of voltage, and grounded if determined necessary (NEMA, 2016).

“this definition hardly describes the intense light and heat, pressure wave, and thermal shock produced”

It is usually during this exercise in which arc flash occurs. Therefore, many facilities and regulations are based on the control of this exercise and the establishment of an Electrical Safety Programme. 

Electrical safety programme

Such an electrical safety programme would normally be set up for each facility and would include developing practices, providing essential training for employees and the performance of a flash hazard analysis. The use and maintenance of PPE would be included, as would the behavioural safety training elements, focusing on human performance tools such as procedure adherence and three-way communication.

An essential training element that I will not go into in this article is obviously the actions to be taken in an emergency with the special focus on dealing with live electrical equipment.

The burden of providing much of these practices and training is normally on the employer, as is the responsibility for ensuring that employees that are qualified continue to comply with safe working practices. Any training conducted should be clearly documented and employees should undergo retraining as needed. 

Retraining, in my personal view, is one element that many organisations and personnel struggle with. The view that once an employee is qualified then that is eternal. The issue that I have with this is that we all know that our knowledge retention time is limited, and especially after a large break away from certain tasks, knowledge has to be reinforced. We put the burden of implementing safe practices onto the employee, we need to ensure they are fully capable of doing so before we task them to do work.

It is not only good practice but often a regulatory requirement, for example in NFPA 70E: Electrical Safety in the Workplace, that a suitable risk assessment for arc flash be undertaken. The main determinations from the assessment are to determine the arc-flash boundary distance and the type of personal protective equipment required. To determine this, we must undertake an incident energy calculation, however, informational tables are also available.

“an employer should conduct an estimation of the potential incident heat energy of any electrical arc”

PPE is a highly important element in the protection of the worker to arc flash hazards. Firstly, many regulations require that the employer conduct an estimation of the incident heat energy of any electrical arc to which a worker could be exposed, OSHA for example.

Importantly this allows the employer to ensure that any workers exposed to the hazard are equipped with protective clothing and other PPE that has an arc rating greater than or equal to the estimated heat energy.

Incident energy

The arc flash boundary shall be the distance at which the incident energy equals 1.2 cal/cm² (5 J/cm²), according to NFPA 70E-2015. One of the units used to measure incident energy is calories per centimetre squared (cal/cm²).

Incident energy is defined in NFPA 70E-2015 as “The amount of thermal energy impressed on a surface, a certain distance from the source, generated during an electrical arc event.”

IEEE 1584 provides the ability to perform calculations that more accurately take into consideration the true electrical conditions of the facility. These calculations are derived from the results of a significant volume of actual testing.

Arc ratings

Arc ratings are determined by carrying out certain tests on garments and other materials which make up the PPE. Like many items that we encounter the legislative framework can be complex but the most common regarding arc ratings are ASTM/NFPA and the IEC.

ASTM F1959/F1959M for example is to determine the arc rating of clothing material whilst ASTM F2621 is to assess the clothing integrity when exposed to an incident energy amount to the arc rating of the clothing material.

Such standards are mirrored by the IEC in IEC 61482-1-2 (identical to EU Regional standard 61482-1-2): Test method for fabrics and garments.

It should be clearly noted that materials or clothing of the same arc protection class do not always offer the same level of arc thermal protection. Two different materials may be Arc Protection Class 2, but one may have a higher arc rating (ATPV or EBT50). The box test method does not allow full differentiation between the arc thermal protective performance of different materials or clothing (Dupont, 2023).

For some multi-layer materials or
multi-garment assemblies, or when the number of wash cycles prior to testing have a major influence on arc rating values, there may be differences between values obtained by ASTM F1959/F1959M and IEC 61482-1-1 (Dupont, 2023).

The uncertainty inherent in the test method is on average about 10%. So, for the practical purpose of selecting protective clothing, all materials and garments with arc rating values within 10% of each other can be considered as providing roughly equivalent electric arc protection (Dupont, 2023).

As per NFPA 70E: Standard for Electrical Safety in the Workplace, a fabric’s arc rating alone does not determine the arc rating of the PPE. A garment needs to have a one-shot test, as per ASTM F2621, or in the case of hoods, ASTM F2178, in order to safely determine the garment system’s Arc Thermal Performance Value (ATPV).

There is a minimum arc rating required in four different PPC categories, with the lowest being CAT 1 (Category 1) which has the lowest arc rating per-square-centimetre, or 4 cal/cm². The next three levels stipulate a minimum arc rating of 8, 25 and 40 calories-per-square-centimetre or cal/cm², respectively. The garment’s ATPV can be found on the label, as per the NFPA regulations.

These categories are listed below.

PPE Category 1: Minimum arc rating 4 cal/cm²

PPE CAT 1 represents the lowest level arc-rated (AR) PPE required. Requiring a single layer of arc-rated PPE, workers need the following clothing.

• Required clothing: Long sleeve shirt (or jacket) and trousers or AR coverall with a minimum arc rating of 4 cal/cm²
• Required face and head protection: Face shield (with “wrap-around” guarding, i.e. a balaclava) or arc flash hood
• As needed: Arc-rated jacket, rainwear, parka, hard hat liner

In addition to AR clothing, the following products are required or to be used as needed.

• Required hand protection: Heavy-duty leather gloves
• Additional PPE: Hard hat, eye protection (glasses, goggles), hearing protection
• Footwear: Leather footwear

PPE Category 2: Minimum arc rating 8 cal/cm²

PPE CAT 2 can likely be met with a single layer of arc-rated PPE. Most companies with exposures requiring CAT 1 typically opt for CAT 2 clothing to cover both categories. However, today, the comfort of PPE CAT 1 and 2 is comparable, so it makes more sense to choose CAT 2 clothing.

In PPE CAT 2, workers need the following clothing:

• Required clothing: Arc-rated long sleeve shirt and trousers, or arc rated coverall with a minimum arc rating of 8 cal/cm²
• Required AR face and head protection: Arc-rated flash hood or face shield, sock hood/balaclava with a minimum arc rating of 8 cal/cm²
• As needed: Arc-rated jacket, rainwear, parka, hard hat liner

In addition to AR clothing, the following products are required or to be used as needed.

• Required hand protection: Heavy-duty leather gloves
• Additional PPE: Hard hat, eye protection (i.e. glasses or goggles), hearing protection
• Footwear: Leather footwear

PPE Category 3: Minimum arc rating 25 cal/cm²

PPE Categories 3 and 4 require additional layers of PPE. Arc flash hoods, rubber insulating gloves and leather protectors, or arc-rated gloves are required. For PPE Category 3, workers need the following clothing:

• Required clothing: Arc-rated flash jacket and AR trousers or AR coverall with a minimum arc rating of 25 cal/cm²
• Required AR face and head protection: Arc-rated flash hood with a minimum arc rating of 25 cal/cm²
• Required AR hand protection: Rubber insulating gloves and leather protectors or arc-rated gloves
• As needed: Arc-rated jacket, rainwear, parka, hard hat liner

In addition to AR clothing, the following PPE is required:

• Additional PPE: Hard hat, eye protection (glasses, goggles), hearing protection (inserts), leather footwear

PPE Category 4: Minimum arc rating 40 cal/cm²

The final PPE Category requires AR clothing with a minimum rating of 40 cal/cm².

• Required clothing: Arc-rated flash jacket and AR trousers or AR coverall with a minimum arc rating of 40 cal/cm²
• Required AR face and head protection: Arc-rated flash hood with a minimum arc rating of 40 cal/cm²
• Required AR hand protection: Rubber insulating gloves and leather protectors or arc-rated gloves
• As needed: Arc-rated jacket, rainwear, parka, hard hat liner

(NFPA, 2021)

Principal injuries

In low voltage incidents, the principal injuries result from the direct contact of the victim with the current while, as we have stated previously, the high voltage shocks carry the electric current to the victim without physically making contact.

The arcing can produce temperatures as high as 35,000° and, as such, may cause severe burns, hearing loss, eye injuries, skin damage from blasts of molten metal, lung damage, and blast injuries.

The one critical factor that influences the severity of direct contact with electrical injury is the type of current to which an individual has been exposed. Surprisingly for many it is indicated that exposure to alternating current (AC), the form of current typically found in homes and workplaces, is considered to be three times more dangerous than exposure to direct current (DC) of the same voltage because it is more likely to result in muscle tetany (involuntary contraction of the muscles), extending the duration of exposure (Cooper, 1995).

Further, the exit wounds produced by direct contact with DC current are also more discrete than those produced by AC current (Bernius and Lubin 2009).

Additional factors that determine the severity of injuries resulting from direct contact with electricity include the strength of the current, and the duration of exposure. The strength of an electrical current, expressed in amperes, is a measure of the energy that flows through a conductor and is a critical determinant in the amount of heat that is discharged to an object (Cooper and Price, 2002).

Our first barrier of resistance to electrical current is the skin. However, its resistance varies between individuals and conditions. Skin that is wet will naturally offer minimal resistance and will in fact maximise the current to which it is exposed.

The thickness of the skin also makes a difference to resistance, the thicker and more calloused the skin the poorer it is of a conductor of electrical current (Koumbourlis, 2002).

One thing of high concern is that from 1992 to 2002, 47% of workplace electrocutions took place in the construction industry (Cawley and Homce, 2006) and construction workers have been found to be approximately four times more likely to be victims of workplace electrocution than workers in all other industries combined (Ore and Casini, 1996). Unfortunately, data from more regionally specific sources are not so freely available, but I cannot think of any reason that there should be any major difference in correlation. 

In addition to any effects, the injury may physically affect job performance after any incident. The neurological effects may encompass behavioural changes, as well as memory and attention issues, and irritability, anger and physically aggressive behaviours have been noted in electrical injury victims with no prior history of mood disorders, creating evident strains in the work and personal environments.

Medical literature seems to clearly indicate that electrical injuries represent an unusually severe form of injury and are oftentimes accompanied by tremendous physical, emotional, and psychological complications.

Conclusion

An arc flash is a serious hazard that is potentially devastating to those exposed to it.

Many regulations and the requirements for employers to have defined and implemented processes in place can be an aid to workers who are exposed to electricity. This is done by providing them an understanding of how to reduce the probability of an arc-flash event and the devastating effect from one. 

However, the resulting injuries that still occur seem to indicate that just because we have formally processed this does not assure the enforcement of safe working conditions, compliance to standards, and the availability of training materials. Compliance with these requirements will support the goal of reducing injuries and downtime of electrical systems.

The severity and quickness of the injuries to personnel, as well as the resulting time away from work, contribute to the high economic cost of electrical injury. However, it should be noted and understood that electrical injuries do not happen in a vacuum. 

Administrative controls and personal protective equipment are hardly unimportant, but as they are designed to focus on the worker rather than the hazard, they are far from optimal.

Even after decades of effort to focus on the organisation in which people operate, it is still seen that when workers are injured the responsibility is often put on their actions, or inactions. This is seen often when there is a failure to wear PPE, rush into work, and even perform work on energised equipment.

It is therefore important to ensure that the workplace systems and behaviour of all employees, from management onwards, are designed to ensure that not only compliance is achieved, but also an environment where an electrical safety culture can thrive.

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REFRENCES

• NEMA, 2016 – NEMA Standards Publication; NEMA ABP 8-2016; Avoid Arc-Flash Occurrences by Following Industry Standards; www.nema.org 
• Dupont, 2023 – From the internet Standards for electric arc protection (dupont.co.uk) accessed 21st April 2023.
• NFPA, 2021 – NFPA 70E^®: Standard for Electrical Safety in the Workplace^® accessed 21st April 2023
• Bernius M, Lubin J (2009) – Electrocution and electrical injuries. In: Cone DC, O’Connor RE, Fowler RI (eds) Emergency medical service clinical practice and systems oversight, vol 1. Kendall Hunt Publishing, Dubuque, IA, pp 44-50
• Cooper MA (1995) – Emergent care in lightning and electrical injuries. Semin Neurol 15:268-278 
• Cooper MA, Price TG (2002) Electrical and lightning injuries. In: Marx JA (ed) Rosen’s emergency medicine: concepts and clinical practice, 5th edn. Mosby, S
• Koumbourlis AC (2002) Electrical injuries. Crit Care Med 30(Suppl):S424–S430
• Cawley JC, Homce GT (2007) Protecting miners from electrical arcing injury. NIOSHTIC-2 No. 20032718. National Institute for Occupational Safety and Health. www.cdc.gov/niosh/mining/ userfi les/works/pdfs/pmfea.pdf. 
• Ore T, Casini V (1996) Electrical fatalities among U.S. construction workers. J Occup Environ Med 38:587–592