Arc Hazard Assessment Software
The Heat Flux Calculator is a free software program created by Alan Privette and is made available to the general public for the purpose of calculating heat flux received at a surface some distance from an electric arc.
Arc Protection Clothing Requirements
Whenever possible, always de-energise circuits before working on or around them.
- OSHA CFR 1910.269 ‘The employer shall ensure that each employee who is exposed to the hazards of flames or electric arcs does not wear clothing that, when exposed to flames or electric arcs, could increase the extent of injury that would be sustained by the employee.’ (I)(6)(iii)
- Clothing made from acetate, nylon, polyester and rayon either pure or blended should not be worn when working in hazardous environments. Clothing made from 100% cotton or wool must be determined acceptable for the conditions the worker will be exposed to. Clothing made from flame-resistant materials, that meet current ASTM F1506, is acceptable.
- ASTM F1506 details the specifications of a textile to be used by an electrical worker as a means of electrical arc protection. A garment must include a label, which states the following information: Tracking I.D. Code, Meets ASTM F1506, Manufacturer’s name, Care Instructions & Fibre Content, Size and ‘Arc Rating’ – ATPV or EBT.
- EN 470-1 is the European standard detailing minimum design and fabric requirements for protective clothing worn in welding and allied processes. Relevant as welding risks - molten metal splash, flame and UV are also found in electrical arcs.
- EN 531 European standard detailing minimum requirements of clothing used to protect against industrial heat and flames. Includes general design requirements and five performance requirements each of which are standards themselves and given code letters below. Clothing complying with EN 531 must meet code A and level 1 or above of at least one of the other performance requirements (B-E).
| ||A||Limited flame spread ||EN 532|
| ||B||Convective Heat ||EN 367|
| ||C||Radiant Heat ||EN 366|
| ||D||Molten aluminium splash||EN 373|
| ||E||Molten iron splash ||EN 373|
EN 61482-1-2:2007 a European standard entitled Live Working - Protective clothing against the thermal hazards of an electric arc. Also called the Box Test, it stipulates testing procedure and pass requirements for testing either a garment or piece of fabric to either a class 1 or higher energy class 2 test. Test parameters are as follows: voltage = 400V, arc duration = 500ms, ac frequency = 50 Hz, phase = single, electrode gap = 3cm, distance to receiving surface = 30cm. Fault current is either 4kA for a class 1 test, or 7kA for a class 2 test.
The electrodes are enclosed in a plaster box with one side open to direct the arc imitating a real life situation. EN 61482-1-2 supercedes ENV 50354. Both are virtually identical apart from EN 61482-1-2 stipulating tighter control tolerances on the electric arc.
|NFPA 70E 2004 Edition|
Table 3-3.9.3 Protective Clothing Characteristics –
Typical Protective Clothing Systems
|Hazardous Risk Catergory||Clothing Description (Number of clothing layers given in brackets)||Total Weight oz./yd2||Minimum ATPV* or EBT* Rating of PPE cal/cm2|
|0||Untreated cotton (1)||4.5-7||-|
|1||FR shirt & FR Trousers (1) ||4.5-8||4|
|2||Cotton underwear plus FR shirt and FR trousers (2)||9-12 ||8|
|3||Cotton underwear plus FR shirt & FR trousers plus FR coverall (3)||16-20||25|
|4||Cotton underwear plus FR shirt & FR trousers plus double layer switching jacket and trousers (4) ||24-30||40|
Always Perform a Hazard Assessment
The NFPA 70E Standard for Electrical Safety Requirements for Employee Workplaces requires employers to perform an Electrical Arc Hazard Assessment. Each situation is unique and needs to be evaluated on its own merits. ASTM F1959 details the standardised test that must be used to determine the thermal protective value of textiles in an electric arc application.
Clothing selected for a particular application shall have an arc protective rating of (EBT or APTV) higher than the potential hazard to prevent the onset of 2nd degree burns. Below are factors affecting potential energy exposures based on the Duke Heat Flux Calculator (click here for download) to compute potential thermal exposure.
Factors Affecting the Extent & Seriousness of Worker Injury when Exposed to Arc Flash
1. Electric arc intensity
- Fault current
- System voltage
- Electrode gap
- Number of phases involved
- Open arc configuration or enclosure
2. Electric arc duration
3. Distance of the worker from the electric arc
4. Type and fit of clothing worn
5. Age and health factors
Clydesdale FR Fabrics
- Clydesdale uses Westex Indura Ultra Soft® exclusively. Indura Ultra Soft® blend of 88% cotton and 12% high tenacity nylon substantially increase the fabric’s abrasion resistance helping the garment last over 50% longer than 100% cotton garments. Plus the new softer feel further enhances the breathable ‘all-weather’ comfort of cotton. The treatment process for Indura flame resistant fabrics forms a long chain flame retardant polymer impregnated into the core of each cotton fibre which gives GUARANTEED FLAME RESISTANCE FOR THE LIFE OF THE GARMENT. An excellent value equation.
- NOMEX® is a man made fibre resistant to heat, flame and chemicals. NOMEX® and KEVLAR® are registered trademarks of E.I. du Pont de Nemours and Company.
Effects of Electrical Shock
Even relatively low voltages can be fatal. For example, electrical shocks produced from common 50 Hz ac power passing from hand to foot for a duration of one second can have the following effects:
|1-3 Milliamps||Tingling Sensation|
|3+ Milliamps||Shock (pain)|
|10+ Milliamps||Muscular Contractions (can’t let go)|
|30+ Milliamps||Respiratory Paralysis (may be fatal)|
|60+ Milliamps||Ventricular Fibrillation (usually fatal)|
|4+ Amps ||Heart Paralysis (fatal)|
|5+ Amps ||Tissue Burning (fatal, vital organs destroyed)|
*ATPV (Arc Thermal Performance Exposure Value) is defined in the ASTM F1959 standard arc test method for flame resistant (FR) fabrics as the incident energy that would just cause the onset of a second degree burn. EBT (Breakopen Threshold Energy) is the average of the five highest incident energy exposure values below the Stoll curve where the fabric does not exhibit breakopen. EBT is reported when ATPV cannot be measured due to FR fabric breakopen.