Towards better arc flash protection

June 4th, 2010, Published in Articles: Energize

One of the most dangerous accidents in the electrical power industry is that of an arc flash incident, also known as arc blasts at higher fault levels. Caused by the failure of electrical insulation or electrical equipment, the result is a massive electrical flashover (at 16 000 to 50 000 A at 600 V, for example), similar to lightning, that can generate a temperature exceeding 20 000°C and a shockwave that can throw a nearby worker several metres through the air.

The major hazard from an arc electrical flash is the terrible burns they can cause to any worker within the arc flash boundary, as fatal burns can occur at up to 3 m away, and the resulting fierce heat will burn or melt most non arc-rated protective clothing and helmets.

However, workers can survive these terrible incidents practically unscathed if they are wearing the correct personal protective clothing and equipment. This why the recent publication of SANS 724, Personal protective equipment and protective clothing against the thermal hazards of an electric arc will help reduce the number of arc flash injuries and fatalities. Currently, South Africa averages at least one arc flash incident per month, with at least one fatality every two months.

Another standard that goes with SANS 724 is SANS 984, IEEE Guide for performing arc-flash hazard calculations. This standard, which has already been published, provides techniques for designers and facility operators to apply in determining the arc-flash hazard distance, and the energy to which employees could be exposed during their work on or near electrical equipment. 

Zarheer Jooma, the technical specialist actively involved with both standards, comments on them as follows:

What other standards are linked to/associated with SANS 724? “When an arc flash hazard exists, the employer needs to take action. This action is broadly categorised into three aspects, namely:

  • Safe working procedures (i.e. lockout, testing, demarcation, use of correct tools etc.) 

  • Providing personal protective equipment and clothing, and

  • Engineering interventions (e.g. internally arc rated electrical apparatus, reduce tripping times, remote operating of breakers etc.)

“SANS 724 focuses on point (2), providing personal protective equipment and clothing. Point (1) is of vital importance and is addressed in the NFPA 70E. Point (3) is left to the employer’s discretion, however some engineering interventions are mentioned in NFPA 70E.

“To determine the correct rating of protective clothing and equipment, the user should use IEEE 1584a. IEEE 1584 has been adopted and published as
SANS 984. It should be noted that, while other engineering calculation guidelines are available, none of these are internationally recognised or available as published standards.

“All other relevant standards are referenced in SANS 724, which is aimed at being a front end standard referencing other standards. IEC 61482-2:2009 and ASTM F1506 are two specification standards which use IEC 61482-1-1/ IEC 61482-1-2 and ASTM F1959 test methods respectively.

“The next step is to formulate a ‘NFPA 70E’ for South Africa. My intention is to amalgamate legislation, industrial best practice and the NFPA 70E into an electrical arc flash safe working standard. I have obtained approval from the national committee to work on such a standard and had been delaying such work until after SANS 724 is published.

What is the next logical step? Should SANS 724 be made compulsory? “I have begun discussions with DoL and DMR who in principle support making SANS 724 compulsory. However, I will need to think about this very carefully and investigate it thoroughly with the help of specialists at the SABS, as I do not want to push up the cost of manufacturing protective clothing and equipment via regulatory costs and bureaucracy.

“I believe that if the end user is educated and can spot a non-compliant product, SANS 724 does not necessarily have to become a compulsory specification.”

“PPE manufacturers can take the lead by acquiring knowledge, understanding
SANS 724 and implementing it. For too long, manufacturers did not have to spend money on testing and certification. Now with SANS 724, they will need to invest in testing.
 
“Presently a successful test on a 90 cal/cm2 fabric could cost about $4750 excluding test materials and freight” Jooma concluded.

Contact Chris Meyer, SABS, Tel 012 428-6732, meyercm@sabs.co.za

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