Measurements of incendivity of electrostatic discharges from textiles used in personal protective clothing

Two methods are described for assessing the ability of electrostatic discharges from an isolated, charged textile to ignite a hydrogen–air mixture. One used a continuous gas flow, the other a fixed volume of gas. In the flowing-gas technique, frequency of ignition for some textiles seemed to show a sigmoidal dependence on the initial surface charge density, σsurf. The threshold value of σsurf for ignition is a characteristic of the textile involved, but shows a relatively weak dependence on surface resistivity. Other textiles appear to show maxima in their ignition probability versus σsurf relationships, while for others, no clear correlation between ignition probability and σsurf could be detected. A good correlation was found between the ‘minimum surface charge density for ignition’ parameter using the flowing-gas technique, and the ‘frequency of ignition’ parameter using the fixed-volume technique. We found that under the conditions described, textiles with conductive threads did not give ignitions provided they were adequately earthed. When isolated, all textiles were capable of causing ignitions regardless of the anti-static strategy employed.