Standard for Electrical Safety in the Workplace (2018)
Australia has adopted the US Standard for arc rated protection NFPA 70E. This standard was developed in conjunction with US federal agency, Occupational Safety and Health Administration (OSHA), by the Standards Council of the National Fire Protection Association (NFPA). It has since been incorporated by Australian safety organisations such as the Australian Energy Council into arc flash guidelines for Australian sites.
The NFPA 70E standard is divided into sections covering safety-related work practices, maintenance requirements, special equipment and installation requirements. Within these sections are tools for meeting NFPA benchmark requirements, including assessment methods, guidelines and work permits, each stipulating precautionary practices that require implementation when working around industrial electrical equipment. Perhaps most importantly, NFPA 70E specifies the required levels of arc rated protection needed for PPE when performing tasks with estimated incident energy exposures.
The NFPA 70E outlines the procedures of crucial risk assessments conducted for personnel working around or directly on live parts of energised electrical equipment. Among the risk assessments outlined in NFPA 70E are the 'Arc flash risk assessment' and a 'Shock risk assessment'. Assessments should be undertaken when any modifications or renovations are made to the environment and at intervals that don't exceed five years. An assessment must take into account the design of the energised device, its machine requirements and any changes made or that are planned to be made to the power source configuration or transformer size.
The arc flash risk assessment will determine the Workplace Health and Safety (WHS) response to the presence of an arc flash hazard. An 'Incident Energy Analysis' will determine the arc flash boundary, safety-related work practices, and the necessary PPE to be worn around certain distances from the energised object. During this analysis, the incident energy is calculated and used as a critical component of an arc flash risk assessment.
Incident Energy Analysis Method
Incident energy (also referred to as heat flux) is the amount of energy that reaches an individual or surface at a distance from an arc during an arc fault. It is measured and expressed in calories/cm2 (or joules/cm2). Generally, the factors contributing to high incident energy are; higher fault current, longer protection clearing time and shorter distances from the arc. The onset of second-degree burns is likely to occur at an exposure of 1.2 cal/cm2 (5 J/cm2) of fault incident energies for one second, a significant threshold for arc fault management.
The incident energy is calculated and used as a critical component of an arc flash risk assessment. The method outlined in NFPA 70E Annex D is the 'Incident energy and arc flash boundary calculation method'. This method predicts the incident energy of an arc flash for a specified set of conditions. These conditions and factors include the voltage, duration of the arc (cycles), nature of the enclosure and distance from the arc to personnel operating. The incident energy exposure level is devised from the distance of the workers face and chest areas, from the arc-source where work is being performed. When calculating the incident energy, the nature of the tool and its assumed properties are considered. Further considerations include whether calculations were made for 'open air' or 'arc in a box', single or multi-phase, voltage limitations and type of equipment/protection.
Another contributing factor to the assignment of appropriate PPE is the 'Arc flash boundary'. These boundaries are drawn around energised equipment and define what PPE should be worn within certain boundaries. The boundaries are set based on the amount of incident energy the worker would be exposed to during a potential arc flash, determining the level of PPE recommended.
Arc flash incident energy calculation method is used to determine the appropriate boundaries around energised equipment. Specific voltage ranges stipulate the area of which 'restricted' approach boundary ends and the 'limited' approach boundary begins.
- Limited: a qualified person must always be present supervising any personnel entering this boundary area.
- Restricted approach boundaries: no qualified personnel shall approach this area or take an conductive object closer to the exposed energized electrical area.
Personal Protective Equipment (PPE) Categories
The abrasion resistance test is carried out using an instrument known as a Martindale tester. The material to be tested is placed on a bed, and a rubbing head of fixed size and pressure, covered with a standard abrasive material, is moved in a circular motion over the test specimen. Pending the abrasion cycle number to breakthrough, the glove receives a score of 1-4 as per the table.
As the abrasion-resistant test attempts to measure ‘wear’ or how long the glove may last during use, its performance score is essential. In the past, different laboratories may have used other abrasive papers on the tester and got varying scores as a result. Under the revised standard, all independent laboratories must now use a standardised abrasive pad in an attempt to ensure scores are more accurate and can be compared more effectively against each other.
|PPE Category||Arc Rating|
|0||Arc rating not required|
|1||< 4 cal/cm2|
|2||< 8 cal/cm2|
|3||< 25 cal/cm2|
|4||< 40 cal/cm2|