Electric Arc Flash Protection

Overview

• Introduction
• Matching Workwear to Potential Arc Flash Hazards
• The Determination of Calorie Levels
• Fault Current Studies and Flash Hazard Analysis
• Australian and New Zealand Standards
• USA Standards
• ASTM/NFPA Standards
• Corporate Analysis and Safety Requirements

Introduction

When workers cannot work de-energised, it is imperative they have suitable and adequate flame retardant (FR) workwear, which matches the potential arc flash hazard they are working with. Workwear, which is not FR will most likely continue to burn after the onset of ignition, resulting in the fabric perhaps dripping and melting into the skin, only increasing the severity of the injuries. FR workwear can under certain circumstances ignite, however, it will extinguish itself after the ignition source, that is the flame or arc, has ceased.

Heat generated from an electric arc is capable of reaching temperatures of around 1000^oC (1832^oF) thus, producing a significant amount of calories.

Matching Workwear
to Potential Arc Flash Hazards

To match appropriate and required workwear to the potential arc flash hazard, companies must determine the calorie level of the hazard their workers are exposed to. The definition of a calorie is the energy required to raise one gram of water one degree Celsius at one atmosphere. Second-degree burns will occur at 1.2 calories per centimetre squared per second (expressed as cal/cm²).

The Determination of Calorie Levels

Two computer software programs are available which can assist companies to determine the energy level (calories) of a potential arc flash hazard. They are;

• The Duke Heat Flux Calculator and,
• Arc Pro II from Kinectrics, Inc., of Toronto, Canada.

The programs ask a number of important and company specific questions relating to the potential hazard situation and once answered, they will calculate a calorie per centimetre squared per second value, which is the level of protection (ATPV rating) the FR workwear must provide to prevent the onset of second-degree burns.

Fault Current Studies and Flash Hazard Analysis

The duration and intensity of electrical arcs is never equal. Companies must conduct Fault Hazard Analysis to quantify the potential arc's calorie level. Once determined, the appropriate type and fabric weight of FR workwear can be ascertained for the given environment. A simple analogy is would workwear with an Arc Thermal Performance Value rating (refer USA Standards section) of say, 8.5 cal/cm² be used in an environment where the Fault Hazard Analysis calculated a rating of say, 26 cal/cm². The level of risk and potential outcome would most probably quantify into certain loss of human life.

SpotNet Distribution highly recommends companies engage the consulting services of an Expert Firm to conduct Fault Current Studies and Flash Hazard Analysis. One such firm is our US Partner, TMK and Associates, Inc., of Cleveland, Ohio. TMK and Associates, Inc. is a leading industry provider for flash hazard analysis and can provide all the necessary guidance regarding application of NFPA 70E, ASTM and OHSA requirements (refer USA Standards section). You can read about the TMK and Associates, Inc. Fault Current Studies and Flash Hazard Analysis overview, by clicking this link to the Services section of their website; www.oshazone.com/services/fault-current.asp

Australian and New Zealand Standards

Australian and New Zealand standards relating to flame and fire resistant clothing for use in protection against heat and fire are summarised as follows;

• AS 2374-1980 - Guide to the selection, care and use of clothing for protection against heat and fire.
• AS 2755.1-1985 - Textile fabrics - Burning behaviour - Determination of ease of ignition of vertically oriented specimens.
• AS 2755.2-1985 - Textile fabrics - Burning behaviour - Measurement of flame spread properties of vertically oriented specimens.
• AS 2755.3-1985 - Textile fabrics - Determination of burning behaviour - Determination of surface burning time.
• AS/NZS 4502.1:1997 - Methods for evaluating clothing against heat and fire - Evaluation of thermal behaviour of materials and material assemblies when exposed to a source of radiant heat.
• AS/NZS 4502.2:1997 - Methods for evaluating clothing against heat and fire - Evaluation of heat transmission of materials and material assemblies when exposed to flame.
• AS/NZS 4502.5:1997 - Methods for evaluating clothing for protection against heat and fire - Evaluation of the contact heat transmission through material and material assemblies.

USA Standards

NFPA 70E requires workers to wear flame retardant workwear, which meets the requirements of ASTM F1506, wherever workers are exposed to an electric arc flash. As discussed above, companies must conduct flash hazard analysis to determine the required level of FR workwear and the appropriate boundary distance from the flash. ASTM F1506 sets out the requirements to protect workers working inside the flash protection boundary by specifying the FR workwear, which suits each hazard risk category having an ATPV rating at least equal to those listed in NFPA 70E, "Protective Clothing Characteristics", summarised below. OSHA (Occupational Safety & Health Administration) has confirmed that FR workwear, which satisfies the requirements of ASTM F1506 are in compliance with OSHA 29 CFR 1910.269 (Electrical Power Generation, Transmission and Distribution, with regard to garments not contributing to burn severity).

Table 3 NFPA 70E
Standard for Electrical Safety Requirements for Employee Workplaces
2000 Edition
Protective Clothing Characteristics

ATPV (Arc Thermal Performance Value) - the higher the value, the more insulated a person is from second-degree burns. Arc Thermal Performance Value is the minimum energy causing the predicted onset of second-degree burns.

HAF (Heat Attenuation Factor) - the higher the HAF percentage, the more heat is blocked by the fabric. The HAF is the total percentage of the arc, which the fabric blocks or prevents from passing through. If the fabric breaks open prior to reaching the second-degree burn level, then a third value, the Ebt, is calculated.

Ebt (Energy of Break Open Threshold) - is energy required to break open the fabric. The energy of break-open threshold is most often reported with multi-layer systems.

ASTM
(American Society for Testing and Materials)

Standards Summary (Electrical Arc Flash Protection)

• F1506-02a - Standard Performance Specification for Flame Resistant Textile Materials for Wearing Apparel for Use by Electrical Workers Exposed to Momentary Electric Arc and Related Thermal Hazards.
• F1891-02b - Standard Specification for Arc and Flame Resistant Rainwear.
• F1930-00 - Standard Test Method for Evaluation of Flame Resistant Clothing for Protection Against Flash Fire Simulations Using an Instrumented Manikin.
• F1958/F1958M-99 - Standard Test Method for Determining the Ignitability of Non-flame-Resistant Materials for Clothing by Electric Arc Exposure Method Using Mannequins.
• F1959/F1959M-99 - Standard Test Method for Determining the Arc Thermal Performance Value of Materials for Clothing.
• F2178-02 - Test Method for Determining The Arc Rating Of Face Protective Products.

NFPA (National Fire Prevention Authority)

NFPA 70E (compatible with OSHA requirements) - Standard for Electrical Safety Requirements for Employee Workplaces, 2000 Edition.

The standard deals with the requirements to safeguard workers from the dangers of fire, shock, arc flash and arc blast.

Corporate Analysis and Safety Requirements

Policies must cover;

1. Companies with employees working in electrical arc environments must undertake Fault Hazard Analysis to determine the intensity of energy from the arc, measured in calories. Once the calorie level is determined, the required FR workwear can also be determined.
2. The ATPV or Ebt rating will indicate the level of energy above which, second-degree burns (or greater) will result. US garment labels must show the ATPV or Ebt rating under the requirements of ASTM F1506-00.
3. The determined calorie level must always match the fabric's ATPV rating. Companies not adhering to this policy expose workers to the possibility of suffering second or third-degree burns.
4. Employees must not be exposed to adverse risk by wearing inappropriate clothing such as, Nylon or non-FR rayon. Synthetic fabric is inclined to drip and melt into the skin only increasing the severity of the burns.