Intrinsically Safe Classifications

Monitor Record Keeping

Monitor Record Keeping

Certain jobs often call for “intrinsically safe” or “explosion-proof” tools and equipment such as lighting and radios. The purpose of this requirement is ensuring that our equipment doesn’t create a source of ignition which in turn could ignite vapors, dusts, mists, or fibers in the atmosphere.

There are several classes of intrinsically safe equipment which have been tested and rated by Underwriter’s Laboratories (UL) and they are broken down into several categories depending on the type of flammable substance and its possible presence in the work areas.

The three classes of flammables are designated I, II, and III.

  • Class I is for flammable gases/vapors or liquids.
  • Class II is for combustible dusts, and
  • Class III for ignitable fibers and flyings.

UL uses both Division and Zone methods, although the Division system seems to be more common.

Under both the Division & Zone systems, work areas are classified based on:

  • The likelihood that the explosive gas atmosphere is present when the equipment is operating;
  • The ignition-related properties of the explosive atmosphere;
  • The maximum surface temperature of the equipment under normal operating conditions; and
  • The protection method(s) used by the equipment to prevent ignition of the surrounding atmosphere.

Class I: Flammable Gases, Vapors or Liquids

These types of fuels are divided up based on their likelihood.

Division 1: This is where ignitable concentrations of flammable gases, vapors or liquids can exist all of the time or some of the time under normal operating conditions.

Division 2: This is where ignitable concentrations of flammable gases, vapors or liquids are not likely to exist under normal operating conditions.

Zones are defined as follows:

Zone 0: Where ignitable concentrations of flammable gases, vapors or liquids are present continuously or for long periods of time under normal operating conditions.

Zone 1: Where ignitable concentrations of flammable gases, vapors or liquids are likely to exist under normal operating conditions.

Zone 2: Where ignitable concentrations of flammable gases, vapors or liquids are not likely to exist under normal operating conditions.

Class II: Combustible Dusts

Division 1: Where ignitable concentrations of combustible dusts can exist all of the time or some of the time under normal operating conditions.

Division 2: Where ignitable concentrations of combustible dusts are not likely to exist under normal operating conditions.

Divisions 1 and 2 are also divided into groups E (metals – Division 1 only), F (coal), and G (grain)

Class III: Ignitable Fibers and Flyings

Class III Area Classification

Division 1: Where easily ignitable fibers or materials producing combustible flyings are handled, manufactured or used.

Division 2: Where easily ignitable fibers are stored or handled.

Once we have a sense of these terms we can see that a headlamp which is rated by the UL as being Class I, Division II would be appropriate to use in most confined space entries when the air is being monitored. If sufficient levels of a combustible gas were encountered and the alarm sounded, the headlamp should not pose an ignition risk while the entrants are evacuating the space. If we were entering a fuel tank under supplied air, then we would want a headlamp certified as being Class I, Division I.

If you have any questions about this, or any other aspect of confined space safety, please call us at 800-551-8763.

Jim Johnson April 17, 2014

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