ANTISTATIC FEATURES IN PROTECTIVE CLOTHING Antistatic fi nishes for limited-use garments generally work by using the moisture of the air to turn the fi nishing- compound into a charge-conductive surface. This means, that if there is enough moisture in the air typically above 25% RH the antistatic property

is active . If however the moisture level is below 25% RH, the antistatic property will be either reduced or perhaps completely absent, depending on the prevailing humidity level.

ANNEXE 7: STATIC ELECTRICITY DISCHARGE

THE ELECTROSTATIC PROPERTIES OF PROTECTIVE CLOTHING The rubbing of a synthetic material against the skin or undergarments is suffi cient to permit electrostatic charges to build up on the fabric. These triboelectric effects of a fabric can generate thousands of volts

and a charge dissipation via a tiny spark from a coverall to a surface of opposite electrical potential in a fl ammable, gaseous, or dust-charged atmosphere could result in a catastrophic explosion.

SAFETY IN EXPLOSIVE ENVIRONMENTS Companies operating in sectors such as the chemical, pharmaceutical, industrial coatings and gas supply industries use combustible materials that can potentially create explosive atmospheres. These

explosive protection zones or EX-Zones are classifi ed into various categories depending on the frequency and length of time that the hazard exists.

Combustible gases and vapours are classifi ed into three explosion groups (IIA, IIB and IIC) according to the minimum amount of energy required to ignite them. The most easily ignitable group is class IIC.

IIA IIB IIC

Acetone Benzene Toulene

Ethylene Ethylene oxide Diethyl ether

Acetylene Hydrogen Carbon disulphide

Source: TRBS 2153 Technische Regel für Betriebssicherheit, Vermeidung von Zündgefahren infolge elektrostatischer Aufl adungen www.baua.de

Table 13. Examples of explosion groups.

Ex protective Zones for gases, vapours and mists

Zone 0

A place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is present continuously or for long periods or frequently.

Zone 1

A place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is likely to occur in normal operation occasionally.

Zone 2

A place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is not likely to occur in normal operation but, if it does occur, will persist for a short period only.

Ex protective Zones for dust

Zone 20 A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is present continuously, or for long periods or frequently.

Zone 21 A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is likely to occur in normal operation occasionally.

Zone 22

A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is not likely to occur in normal operation but, if it does occur, will persist for a short period only.

Source: Directive 99/92/EC

Table 12. Categories of Ex-Zones.

Annexe 770