9.3 The Risk Gap

The reason why I have segmented the process in this way is to give flexibility to the duty holder in how they can gain compliance with best practice. Going back to basics, we have a known hazard, called arc flash, which should get attention in the same way as any other potentially serious hazard. What I would hate to think, is that a duty holder would fail to carry out a risk assessment purely because of a mistaken belief that the only way to proceed is by commissioning a full arc flash study. That could be a costly way to kick the can down the road and to miss the overall point about risk assessment.

In the UK, the HSE expect “that duty holders, in turn, will adopt a sensible and proportionate approach to managing health and safety, focussing on significant risks i.e. those with the potential to cause real harm. In applying the principle of proportionality means that inspectors should take particular account of how far duty holders have fallen short of what the law requires, and the extent of the risks created”. During visits by inspectors, a risk gap analysis is made to determine the actual risks and measure this against the risk accepted by the law or guidance. The sooner that risk assessments are commenced on a sensible footing, and focussing on significant risk, then the more likelihood of bridging that gap between what is happening now and what should be happening.

Figure 9.2 Risk Gap reproduced courtesy of Guardian Electric

9.4 Choices of Approach to Predicting the Hazard

9.4.1 Option 1. Do Nothing.

Not to be recommended although, limited action as a result of a risk assessment is legitimate.

9.4.2 Option 2. Use the Guide.

There are several advantages to using the guide which are:

  • The guide will identify significant risks quickly.
  • It will provide scalability, flexibility and be a steppingstone to a more complex approach, should it be necessary.
  • It is a very low cost and accessible alternative and inclusive for more members of the engineering team.
  • Can easily be adopted into dynamic risk assessments.
  • Provides a source of training and information.
  • Save Money by:
    • Low initial cost of model.
    • Optimising PPE.
    • Reducing training costs.
    • Cost reduction Strategy and commercial contracts and vendor advice should a more complex approach be required.
    • Identify and group low level circuits into categories that can be excluded from complex arc flash studies.

9.4.3 Option 3. Outsource a Study.

If you have concluded that the correct course of action will be to outsource a system study, I hope that it is based upon some of the advice within the guide. Once this decision has been made, the following suggestions may help in obtaining the best possible outcome when commissioning the system study.

Type of software. There is further guidance on complex modelling software given in Chapter 13: Complex Software Guide. Something that the duty holder may need to watch out for is where complex software packages are being used by the company elsewhere in the world. So, if there are other sites within the group, maybe they have gone through a similar learning curve that you may not have to repeat for the sake of a phone call. There may also be a commercial contract in place that may lead to some significant discount. Another issue is the compatibility of the software packages with software already in use perhaps for importing or exporting data.

Which circuits are going to be included? This is where some huge savings can be made. In terms of effort, a 32-ampere low voltage final circuit takes nearly as much time to survey as a 3200-ampere transformer air circuit breaker. Circuits below 100 amperes will probably be far more abundant and outnumber larger power circuits by a factor of 10 plus. By using the guide, you can determine a cut off limit for low voltage circuits which will drastically reduce the number of circuits in the overall study. For instance, if you were look at the tier 3 calculator for devices less than 125A calculator the incident energy at a working distance of 450mm, devices below 100 amps will clear circuits very quickly except for very low fault levels. These low incident energy level circuits can be confirmed from the calculator, then grouped and then categorised as being below 1.2cal/cm2. As such they can then be removed from the overall modelling study which will reduce overall costs.

Remember that a burn will still be possible from an arc flash incident as the hands may be closer to the arc when testing for instance. This is where I would always advise on the use of insulating gloves with leather over protectors regardless of circuit size for testing. Use of the tools with the guide will allow you to create a cut off criteria in order to identify which circuits will be excluded from the study.

Choosing a Competent Contractor. There are vendors that are available who claim to be proficient in arc flash studies and it may help to ask a number of questions to ascertain the correct credentials. This is in addition to competence assessment that is covered in Chapter 6: Process, Policies & Procedures:

  • Experience
    • What arc flash studies has the prospective vendor completed?
    • Are there suitable references from a previous client?
    • Have they had experience on similar sites to your own?
  • European approach
    • Can they demonstrate a European approach to electrical safety?
    • Ask to see outputs from studies, do labels follow European signs and symbology rules?
  • Electrical safety credentials
    • Are they providing the study from a purely academic standpoint?
    • Do they provide electrical safety advice alongside the numerical output from the study?
  • Training
    • Can they provide and include electrical safety training which incorporates arc flash to your employees and contractors?
  • Data Collection
    • Has the vendor a process for data collection?
    • How does it compare with the planning aspects of Chapter 8: Data Collection?
    • What safety precautions are planned for inspections near live equipment?
  • Software (There is further guidance on complex modelling software given in Chapter 13: Complex Software Guide)
    • Is their software package being used by the company elsewhere in the world?
    • Do they provide a free viewer or is the output restricted to written reports and spreadsheets?
    • Does the system model and data belong to you or the vendor?
    • What is the cost of purchasing a copy of the software for future circuit additions?
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