The standard includes minimum performance criteria for arc resistance of harnesses for workers who may be exposed to thermal hazards of momentary electric arcs or flame. The goal of the standard is to provide additional levels of protection to workers in high-voltage electrical environments.
Included in the new standard are criteria for:
- arc flash exposure and drop testing for harnesses;
- prohibition against harness ignition or melting as a result of arc flash exposure;
- harness sizing requirements;
- harness design requirements.
Description of the hazardClimbers working near energized electrical sources face special hazards due to sudden, unexpected arc flashes that can ignite or melt clothing and protective gear. The concern is for workers equipped with standard fall protection harnesses that may be damaged by the high heat of an electric arc and possibly fail to arrest a subsequent fall.
Investigation of past accidents involving arc flash revealed the danger of injury to workers burned by the ignition and melting of clothing following the initial flash of electrical energy. The new standard addresses this potential hazard with criteria that prohibit materials in the construction of safety harnesses capable of sustaining an open flame, or melting after arc flash exposure.
Harness testingThe objective of the new standard is to verify by testing that fall protection harnesses will continue to perform as intended to stop a fall after being exposed to a severe electric arc flash. Testing is performed in two consecutive steps: first, an arc flash exposure, and next, by dynamic drop testing.
The severity of arc flash is measured in terms of the heat energy imparted by the electric current. The ASTM F887 standard specifies exposures of 40 cal/cm2. This exposure level is considered to be a very high risk category, typically encountered only by working on energized parts like voltage-testing in switchgear greater than 1,000 volts.
The test method is defined by another ASTM standard, F1958/ F1958M â€“ 99, â€œStandard Test Method for Determining the Ignitability of Non-flame-Resistant Materials for Clothing by Electric Arc Exposure Method Using Mannequins.â€ As the title implies, arc testing of the harness is performed with the harness fitted to a test torso. The harness is then hit with a momentary arc of high-voltage electrical current by electrodes placed close to the test specimen. Harnesses are tested separately with exposure at the front and back.
The arc exposure test of full-body harnesses also contains criteria for ignition and melting. No part of the harness is permitted more than five seconds of after-flame, nor is melting or dripping permitted following the arc flash exposure.
Following the arc flash exposure, each harness is subjected to a feet-first and head-first drop test according to the procedures in ANSI Z359.1-1992(R1999), â€œSafety Requirements for Personal Fall Arrest Systems, Subsystems and Components.â€ These tests subject each arc-exposed harness to a 6-ft. free-fall with a 220-pound mass. To pass these tests, the harnesses must retain the torso test mass in an upright position.