KANBrief 3/09
During work on electrical installations, fault arcs may occur which release enormous quantities of energy within fractions of a second and present a risk of fatal injury for persons in the vicinity. In order for the tremendous dangers to be combated better in practice, a KAN working group has begun by formulating targets and requirements for research regarding measures for protection against fault arcs.
Fault arcs involve the discharge of energy in the form of extreme heat, accompanied by a pressure wave, a loud blast, a flash, and radiation. This range of different forms of exposure is not the only reason for the high complexity of risk assessment on electrical installations. In particular, in contrast to noise exposure, for example, the risks cannot be clearly quantified. The difficulty lies in determining, from the characteristics of the installation and the potential emissions, the actual exposure acting upon human beings, particularly in the form of incident energy. The operator, however, is able to analyse the hazard and to decide whether and under what conditions he may allow his employees to work safely only on the basis of the installation characteristics. Based upon a risk assessment, he may have to provide personal protective equipment which reduces the energy able to act upon persons in the event of a fault arc sufficiently for example for second-degree skin burns to be prevented.
The DKE is currently drawing up methods for the characterization of installations. These are intended to enable the operator to classify his installations according to the potential incident energy levels in such a way that he can select PPE suitable for use in conjunction with them. The question of which PPE is suitable for which incident energy is at the same time the subject of the EN (IEC) 61482: "Live working – Protective clothing against the thermal hazards of an electric arc“ series of standards governing protective clothing against electric arcs. In contrast to the more subjective, purely visual methods used to date (as for example in the former ENV 50354), the test methods set out in this series exploit defi ned incident energy levels in order to measure the thermal penetration through PPE and thus to defi ne protective classes.
Discussion of PPE standardization
In accordance with EN 61482-1-2, a mean value of 423 kJ/m2 is assumed for the thermal energy in tests of the protective clothing of the highest protective class (Class 2). Since higher incident energies may however be encountered during work on arc-tested low-voltage or medium-voltage installations when open, critics of the standard question its relevance to practical conditions, and suggest for example that a third protective class may be necessary. From a prevention perspective, however, it is debatable whether work involving such high potential incident energy levels should ever be performed live, even with PPE providing even better thermal protection, since such PPE does not provide protection against the consequences of other hazards, such as blasts and pressure waves.
As is the case with many other PPE standards, the test requirements contained in EN 61482- 1-2 (and IEC 61482-2) do not precisely refl ect the characteristics of installations actually found in practice. Instead, they use other parameters, better suited to testing, in order to simulate the exposure against which the PPE is to provide protection. This frequently leads to confusion among operators who incorrectly assume that the PPE tested in accordance with the standard is suitable for use only in installations sharing the same characteristics as the test apparatus. In practice, however, the simulated incident energy levels cover a large proportion of the possible exposures.
Common targets
A KAN working group has agreed common targets which are intended to assure even greater protection against fault arcs. Some of these targets are to be incorporated into standardization work:
The working group will continue to address these issues.
Corado Mattiuzzo
mattiuzzo@kan.de