Anyone working on or near live electrical equipment knows that there is one obvious danger that they must protect themselves against – electrocution. Electrocution is one of the leading causes of workplace fatalities around the world, being fifth in the United States for worker deaths.
Most electrical accidents are not the result of direct electric shocks, however, but instead result from a particularly hazardous type of shorting fault, called an arc fault or flash, that can cause considerable damage to equipment and serious injury to nearby workers.
It has been estimated that up to 77% of all electrical injuries are caused by arc flash incidents. The potential dangers of an arc flash can be reduced by being able to clearly understand shock hazards and the proper protection needed while working with energised electrical equipment. Following the relevant safety guidelines and using personal protective equipment (PPE) could mean the difference between life or death for a worker.
The power of the arc
Arc flash is the sudden release of electrical energy through the air when insulation or air separation causes a high voltage gap between conductors, leading to a breakdown. Arc flashes can be caused in a variety of ways:
• Coming close to a high amp source with a conductive object can cause the electricity to flash over • Dropping a tool or otherwise creating a spark can ignite an arc flash • Equipment failure due to use of substandard parts, improper installation, or even normal wear and tear • Breaks or gaps in insulation • Dust, corrosion or other impurities on the surface of the conductor
An arc flash gives off thermal radiation, or heat, and bright, intense light that can cause burns. Temperatures have been recorded as high as 35,000˚ F, which is four times hotter than the surface of the sun.
High voltage arcs can also produce considerable pressure waves by rapidly heating the air and creating a blast. This pressure burst can hit a worker with great force and send molten metal droplets from melted copper and aluminum electrical components great distances, at extremely high velocities.
To put the power of arc flash into perspective, take a look at the following comparisons: • Hot summer day: 100 degrees F (311K) • Surface of the Sun: 8,540 degrees F (5,000 K) • Arc at arc terminals: 35,540 degrees F (20,000+ K)
The need for protection
The intense, violent nature of an arc flash can cause serious injury to an employee which can affect all areas of the body – even result in death. Without proper protection, injury is inevitable. Arc flash has the ability to severely burn human skin and ignite the clothing of anyone within several feet of the incident. Treatment for such incidents can involve years of skin grafts.
Projectiles, molten debris, and the intense UV radiation associated with the flash can cause retinal and structural eye damage. Superheated vapours can injure lungs and impair breathing. The thermo-acoustic blast can damage hearing with ruptured eardrums, cause collapsed lungs, and damage other internal organs. The blast can knock personnel off their feet and falls may result in broken bones, or lead to electrocution or further injuries to other parts of the body.
Unfortunately, it’s not uncommon for an injured employee to never regain their past quality of life. Extended medical care is often required, sometimes costing in excess of $1,000,000 over time. These costs are often charged to the company, which may end up being involved in expensive lawsuits with victims and their families. An incident of this magnitude also negatively affects workplace productivity, through lower morale and the need to re-appropriate other employees’ tasks and responsibilities to compensate for the injured worker.
In addition to the human consequences, a serious arc flash will damage or even completely destroy the affected equipment, leading to extensive downtime and expensive replacement and repair, and possibly causing the line or even the entire plant to shut down for a period of time.
An incident may also represent a failure on the part of the employer to comply with industry guidelines and regulations. This could result in a fine, litigation fees, increased insurance costs, expensive legal actions, and accident investigations – all of which are costly.
Follow regulation to save lives
With the rising concern for arc flash accidents and the potential for serious injury or death, arc flash is an important topic within the safety industry. To increase safety and ensure compliance throughout your workplace, it is critical that both employers and employees know how to identify arc flash hazards in your facilities, utilise safe work practises, and understand labels and other awareness aids, keeping everyone up to date on regulation and reinforcing safe behaviour.
NFPA 70E is the leading internationally recognised safety standard for arc flash prevention and protection. It covers shock hazard in a similar way to European standards, although there are differences. In addition, it requires risk assessment for arc flash hazard, meaning that before work can be carried out near energised conductors the following must be done:
• The hazard must be known – Employers must conduct a thorough arc flash hazard analysis to determine the amount of thermal energy that could be generated in an arc flash incident, establishing the shock and protection boundary around the potential source
• Measures must be taken to reduce risk – Warning labels on the equipment must identify the hazard and summarise this information
• Appropriate PPE worn – Appropriate arc-rated protective clothing and other personal protective equipment must be worn when risk cannot be reduced through other means and when employees cross the boundary while they work on or near exposed ‘live’ parts. It is important, however, to remember that NFPA 70E does not protect personnel against the effects of arc blast
Requirements for risk assessment for arc flash hazard as covered in the NFPA 70E are currently not present in European codes and standards.
Here are some important safety recommendations from NFPA 70E on how to establish an ‘electrically safe work condition’ before working on a circuit by de-energising it: • Identifying all power sources • Interrupting the load and disconnecting power • Visually verifying that a disconnect has opened the circuit • Locking out and tagging the circuit • Testing for voltage • Grounding all power conductors
In addition, under the NFPA 70E it is required to use a written permit system on or near energised parts that are more than 50 volts for planning and conducting work. Tools, meters and other equipment must also be suitable for the voltage and current levels present when performing all electrical work.
All of the steps listed previously regarding NFPA 70E require the use of appropriate personal protective equipment for shock and arc flash protection, such as safety glasses, voltage rated gloves, fire-resistant (FR) work clothes, arc-rated face shields, flash suits with hoods, and hearing protection.
In Europe, the standards published by the International Electrotechnical Commission (IEC) in IEC 298 are widely referenced. Arc flash hazard analysis on European power systems can be done using the IEEE 1584 standard, as recommended by NFPA 70E.
By performing a short-circuit analysis and protective device coordination study, hazard levels can be calculated using equations derived from laboratory tests. The UK being in compliance with EAWR (Electricity at Work Regulations) 1989, section 5 is required.
Many other countries have their own broadly similar standards and regulations. In the United States, there are several regulations that apply to personnel working with energised electrical equipment under the Occupational Safety and Health Administration (OSHA) and the National Fire Protection Association (NFPA).
OSHA cites and fines employers for failure to protect employees from the dangers of arc flash. For guidelines on best practises for protecting employees, OSHA refers employers to the 2012 edition of the NFPA 70E standard. Here are the four main regulations relating to arc flash in the United States:
• OSHA 29 CFR-1910 – Subpart S provides the legal requirement for employers to guard against arc flash hazards. It sets general requirements for safe work practises, PPE, and hazard analysis
• NFPA 70 – called the National Electrical Code (NEC), provides a requirement for arc flash labels
• NFPA 70E – ‘Standard for Electrical Safety in the Workplace’, outlines the specific procedures and practises to be followed for OSHA compliance and safety when working on live equipment
• IEEE 1584 – ‘Guide to Performing Arc Flash Calculations’, provides the formulas necessary for analysing arc flash hazards
Canada’s regulations on arc flash can be found in CSA Z462 and are addressed legislatively at both the provincial and federal levels. All provincial occupational health and safety acts have a general duty clause requiring employers to take reasonable precautions to ensure their employees’ health and safety. For example, OSHA Occupational Health and Safety Act of Ontario sets out responsibility on employers to “take every precaution reasonable in the circumstances for the protection of workers.” It places the responsibility on employers to anticipate those hazards peculiar to the workplace. Under OSHA, corporations face potential fines of $600,000 per offence, with individuals facing potential fines of $27,500, or 12 months in jail. Throughout the rest of the world, either NFPA 70E or IEC 298 standards may be followed.
Personal Protective Equipment
While safety is the paramount concern, it is important to use proper personal protective equipment fitted to stand up against high heat and electrical current as the last line of defence against arc flash. The potential effects of an arc flash blast can be reduced by using PPE. It is not, however, intended to prevent all injuries, but to mitigate the impact of an arc flash, should one occur.
In the United States, OSHA requires workers who work around electrical hazards to have head-to-toe protection, including hard hats, face shields, flame resistant neck protection and ear protection. Also, they should be outfitted with flame resistant work suits, insulated rubber gloves – preferably with leather protectors – and insulated leather footwear. All materials must be metal-free to avoid the possibility of arc flash, whereby a fault creates an electrical contact with the worker.
Personal protective equipment for arc flash includes: 1. Gloves Gloves are a crucial piece of personal protective equipment for electrical workers, combining high dielectric and physical strength with flexibility and durability. Depending on the hazard level of work, there are three kinds of gloves to choose from: • Rubber insulating – Made of rubber, the dexterity of these gloves makes working with small parts easy • Electrical protective gloves – These rubber gloves combine the required dielectric properties of an electrical protective glove with flexibility, strength and durability, making them ideal for use in industries such as electrical contracting, power and communication utilities, and manufacturing • Leather protector gloves – These gloves are made to go over your rubber gloves to protect them against cuts, abrasions, and punctures
2. Clothing Employees must wear protective clothing based upon the incident energy associated with the task being performed. Other PPE may be required for specific tasks with various weight fabrics and can be provided as a shirt and trousers, or as coveralls, or as a combination for increased protection. Generally, the higher degree of protection is provided by heavier weight fabrics and/or by layering combinations of one or more layers of FR clothing.
For example, flame-resistant (FR) clothing must be worn wherever there is possible exposure to an electric arc flash above the threshold incident-energy level for a second degree burn, and it should cover all ignitable clothing and allow for movement and visibility. Flame-resistant suits are made of a suitable calibre to reduce the indecent energy on the body so any burns suffered are not life threatening.
In some cases, one or more layers of FR clothing are worn over flammable, non melting clothing. Used alone, non melting, flammable clothing can provide protection at low incident energy levels.
Clothing made from acetate, nylon, polyester, acrylic, polyethylene and rayon, in either pure or blended forms, should not be worn when working in hazardous environments.
3. Headgear Employees should wear nonconductive head protection wherever there is a danger of head injury from electric shock, or burns due to contact with live parts or from flying objects resulting from electrical explosion. Headgear also includes nonconductive protective equipment for the face, neck and chin whenever there is a danger of injury. When necessary, face shields should have an arc rating suitable for the arc flash exposure, and eye protection, such as safety glasses or goggles, must be worn under face shields or hoods.
4. Foot protection Dielectric overshoes should be required where insulated footwear is used as protection against step and touch potential. Insulated soles should not be used as primary electrical protection.
5. Insulated tools and equipment Employees should use insulated tools and/or handling equipment when working around energised electrical equipment and/or exposed live parts where tools or handling equipment might make accidental contact. Insulated tools should be protected from damage to the insulating material, and can be composed of impact-resistant and flame-retardant material.
Insulated tools have requirements that apply to them while being used and should be rated for the voltages on which they are used. Insulated tools should also be designed and constructed for the environment to which they are exposed and the manner in which they are used.
An organisation in which a worker is around energised electrical equipment has a responsibility to prevent arc flash injuries according to the NFPA 70E standard. Employers are now responsible to provide a safety analysis of the workplace and develop engineering controls to eliminate hazards.
To achieve this, they must assess workplace arc flash risks, document the assessment, and also select, have available, and require the use of appropriate tools, correct PPE, and regular maintenance of equipment and training. Organisations can also engineer new or retrofitted facilities, incorporating the latest safety technology to reduce the potential for arc flash exposure and to keep the facility safer in general for its employees.
Commit to safety
A commitment to training is a commitment to safety. A company can reduce its exposure to the risk of arc flash hazard by acknowledging that a hazard does exist, assessing that hazard’s magnitude, and then developing an Arc Flash Hazard Programme. Partnerships with equipment suppliers can bring innovative and safer technology to the workplace.
Most importantly, management can demonstrate the value of safety to their employees, customers, and other stakeholders through their actions, which creates a positive safety climate where people watch out for each other. Remember, there is no personal protective equipment that trumps safe procedure.
Published: 04th Sep 2013 in Health and Safety International