Electrical Safety – assessing for electrical hazards
Dennis Neitzel - Director Emeritus - AVO training institute Inc.
Wherever electrical equipment and systems are installed, electrical hazards exist. The most common of these hazards are shock, arc flash, and arc blast, and they must be identified and assessed to determine if and where each of them exist. In addition, businesses must assess the potential for exposure of personnel who work on, near, or interact with the electrical equipment. Electrical standards and regulations worldwide include requirements for assessing the workplace to identify hazards where employees would be required to wear personal protective equipment (PPE).
An understanding of electrical hazards is essential for recognising the need to assess these hazards and the risks associated with them. Electrical hazards include shock or electrocution, arc flash, and arc blast.
A. Electrical Shock
Electrical shock or electrocution occurs when there is a difference in electrical potential between one part of a person’s body and another. When a person’s body completes the circuit between two energised conductors or between an energised conductor and a grounded surface or conductor, current will flow through the person’s body. A shock can produce various effects, from a slight tingle to immediate cardiac arrest. It generally takes very little current – as little as one-tenth (0.1) of an ampere – to cause the heart to go into fibrillation.
B. Electrical Arc Flash
Studies of electrical incidents reveal that a large number of these involve burns from electrical arc flash. There is a serious misconception throughout industry that electrical arc flash is only a product of high voltages. In reality however, arc flash is not voltage sensitive, but is a product of short-circuit current and the overcurrent protective device clearing time. In most cases it is possible to generate higher arc energy from a low-voltage source than from a high-voltage source.
C. Electrical Arc Blast
Arc blast hazard is created by a rapid expansion of the air caused by an electrical arc. According to several studies on the subject, the pressures from an arc are developed from three sources:
1) the available short-circuit current;
2) the expansion of the metal boiling and vaporising;
and 3) the heating of the air by passage of the arc through it. Another product of arc blast is the creation of high sound levels, which have been documented to reach levels of up to 165 dB during arc blast tests.
Electrical Hazard Assessment
Various standards and regulations require the employer to assess the workplace to determine if hazards are present, or are likely to be present, which would require the use of PPE. Electrical hazards fall into this general requirement. Many standards address these along with the risk assessment considerations for all hazards, including the electrical hazards. Identifying electrical hazards is a necessary part of performing the risk assessments.
Electrical Hazard Risk Assessments
The workplace must be assessed to determine where hazards exist or may exist. If such hazards are present, or likely to be present, the employer must:
♦ Select, and have each employee exposed to the hazards use the types of PPE that will protect them from the hazards identified
♦ Communicate selection decisions to each affected employee
♦ Select PPE that properly fits the employee
The following information is provided to clarify the electrical hazards risk assessment requirements.
A. Working While Exposed to Electrical Hazards
This section provides the initial requirements and guidance for performing the electrical hazard risk assessments. When electrical conductors and circuit parts are energized, or can become energized, safety-related work practices must be:
♦ Used to safeguard employees from injury due to the electrical hazards.
♦ Consistent with the electrical hazards and the associated risk to the employee.
♦ Determined before the qualified person is exposed to the electrical hazards.
The electrical hazards, along with the risks to personnel, are determined by completing the shock and arc flash risk assessments. In order to reduce risk, the electrical conductors and circuit parts should be placed in an electrically safe condition before any work is performed.
B. Shock Risk Assessment
The shock risk assessment determines:
♦ The voltage to which employees will be exposed
♦ The shock protection boundary requirements
♦ The PPE necessary to minimise the possibility of electric shock to personnel
The shock protection boundaries are generally identified as the limited and restricted approach boundaries. The boundaries are based on the voltage. The outermost boundary will establish the placement of the alerting techniques to be used, which include safety signs and tags, barricades, and attendants, as applicable.
C. Arc Flash Risk Assessment
The arc flash risk assessment must be performed to determine if an arc flash hazard exists, to identify safe work practices, to establish the arc flash boundary, and to select appropriate PPE.
The arc flash risk assessment must be evaluated and updated when any major modifications or renovations of the electrical systems and should be conducted at intervals that do not exceed five years. This risk assessment takes into consideration:
♦ Design of the overcurrent protective device
♦ Opening time of the overcurrent protective device
♦ Condition of maintenance
The results of the arc flash risk assessment must be documented.
Electrical Safety Programme
The employer should implement an overall electrical safety programme that addresses work performed where there is a risk of electrical hazards. The program should include administrative controls such as:
♦ Safety-related work practices
♦ Verification of proper maintenance
♦ Alerting techniques
♦ Auditing requirement
♦ Training requirements
Other subjects that should be included are:
♦ Consideration of the condition of maintenance of electrical equipment
♦ Providing an awareness of the potential electrical hazards
♦ Self-discipline of all employees performing electrical work
♦ Method to convey to employees the electrical safety principles and controls
♦ Procedures developed to determine:
• Tasks to be performed
• Qualification requirements
• Identify hazards and assess risk
• Identify safe working practices
• Identify the PPE required to protect employees
• A risk assessment procedure to address personnel who have a potential exposure to electrical hazards
♦ A job briefing must be conducted
♦ Auditing of the electrical safety programme and field work
Electrical hazards are universal throughout industrial power systems and equipment. Employees who operate, maintain or interact with electrical power systems and equipment must have a clear understanding of the electrical hazards associated with the jobs and tasks that they perform and the safety requirements that must be met to provide protection. The requirements for identifying electrical hazards, performing risk assessments, developing and implementing safety programmes and safe work procedures, providing all required PPE, and providing training for all employees who may be exposed to electrical hazards, must be accomplished before work is started that could expose personnel to electrical hazards.