The 4P methodology for electric arc flash hazard assessment

By taking a holistic approach to arc flash risk and protection, the 4P Methodology simplifies hazard assessment to four steps:

• Predict severity of arc flash 
• Prevent damage through hazard mitigation
• Protect workers from residual hazard
• Publish results

With hazard mitigation - and risk reduction - implemented, any residual risk of injury to individuals can be mitigated with PPE. Finally, the results can be published to inform behaviour and guide PPE usage.

Arc Flash Hazard Assessment

PARAMETERS RESULTING FROM SEVERITY ASSESSMENT

The results of the arc flash hazard assessment are commonly given by the following two parameters: Incident Energy and Arc Flash Boundary.

Incident Energy

Incident Energy (kJ/m2 or cal/cm2) is the heat energy resulting from an electric arc, measured at a unit surface area at a specified distance from the electric arc.

It defines arc flash severity at the worker’s distance from the electric arc. 1.2cal/cm2 applied to skin for 1 second results roughly in the threshold energy for onset of second-degree burns.

Arc Flash Boundary

“The boundary within which a person could receive a second-degree burn from an arc flash incident”. (IEEE 1584)

Arc Flash Risk Prevention

PREVENTING THERMAL EFFECTS WITH HAZARD MITIGATION AND RISK REDUCTION

Best practice for prevention of arc flash thermal effects is to mitigate the hazards and reduce the risks. This can be done in a number of ways.

Hazard Mitigation

Assess if there are safer alternatives that can be used to replace working with the potentially hazardous electrical equipment?

When live work is being carried out, can you change the protection settings to provide greater worker protection?

Have you re-calculated the hazard in all conditions?

Risk Reduction

Select the most reliable electrical equipment available

Allow for human factors, and ensure that workers and contractors:

• are aware of the hazards 
• are trained and competent 
• have clearly allocated responsibilities
• have clear intervention procedures. 

See why it can be effective to put in place hazard mitigation measures.

Arc Flash Personal Protective Equipment

Arc flash PPE is PPE for electrical work, where there is risk for the worker being exposed to the effects of an electrical arc, for example when carrying out live work on electrical switchgear.

MAPPING AND PROTECTING AGAINST RESIDUAL ARC FLASH RISK

Once all possible practical measures are in place to mitigate hazards, any residual risk at the workplace should be mapped. The risk level can be assessed by considering:

• potential power of the arc flash
• duration of work being undertaken
• distance between worker and arc flash
• frequency of work

Residual risk can then be mitigated by using the optimum combination of Arc Flash PPE for:

• Body
• Hands
• Head
• Eyes
• Face

Optimum Arc Flash Personal Protection Equipment

All Arc Flash PPE should be compliant with local legislation in addition to relevant international or national standards. A comprehensive range of arc flash PPE is available to protect workers from head to toe to avoid injury at all costs:

Protection for the body:

Arc flash protective clothing (sometimes referred to as “arc protective clothing”, “arc flash clothing”, “arc clothing” or “flash clothing”) can be layered to provide additional mechanical, thermal and chemical protection. Lightweight comfortable layering can offer a relevant level of protection whilst ensuring the worker’s movements are not restricted.

Single and multi-layer systems can include several items of clothing including:

• shirts,
• polo shirts,
• sweatshirts
• jackets
• trousers
• coveralls
• multi-layer jackets and trousers
• high-visibility / foul weather gear
• multi-layer suits for short duration wear when dealing with high-level Incident Energy risks
• underwear (non-melting), to provide additional heat protection

Each item of garment system (e.g. jacket with a shirt ) must be flame-resistant; whilst it is not necessary that every item has an arc-rating, the garment system as a whole has to have an arc rating. The garment system must also carry a marking showing the value of its arc rating, i.e. the value of its arc flash protection performance.

Note: The terms “arc resistant clothing” or “arc proof clothing” sometimes used are somewhat misleading, as all arc flash protective clothing will be damaged by a strong enough electric arc, and would in any case be discarded once exposed to an electric arc.

Protection for the hands:

Arc flash gloves or glove systems are certified for protection against the heat of an electric arc. Usually, for live working tasks, one combines them with insulating gloves to provide additional protection against electric shock in case of accidental contact with energized conductors.; in this instance, arc flash gloves should also be insulated or combined with insulating gloves to an arc flash glove system.

Protection for the eyes, face & head:

Arc flash protection for the eyes, face and head will prevent skin burns caused by the heat of an electric arc. Arc flash eye glasses, an arc flash visor and/or an arc face shield can also protect eyes against bright light and UV and IR radiation, whilst still permitting good, non-distorted vision and good colour recognition.

Publish – Information and Training

SHARING INFORMATION WITHIN YOUR ORGANISATION

Information gathered regarding hazard risk assessment only has practical value when shared within your organisation. You should therefore record details of all relevant electrical equipment on your premises, and its hazard calculation.

Where relevant, equipment should be clearly labelled with its hazard risk, and precise written instructions provided for each job and work place.

It is also essential that anyone who works on or near to electrical equipment is fully trained in safe working practices.