Fire extinguishers for electrical installations — there is no separate "fire class E", but there is a separate voltage test

The arc flash guide briefly mentions that only a CO₂ or powder extinguisher should be used for a fire caused by an electrical fault. This article goes deeper into why that is the case, and into the distinction between an extinguisher's fire-class rating and the separate suitability assessment for use on installations that may still be live.

There is no official "fire class E" for electricity

EN 2 (Classification of fires) defines classes A (solids), B (liquids), C (gases), D (metals) and F (cooking fats/oils). There is no class E for electrical fires: the European reasoning is that electricity is an ignition source, not a combustible substance in itself — the burning material (for example a cable's plastic insulation) already falls under class A. Some older extinguishers, and some non-European classifications, carry an electrical symbol (a lightning bolt), but this is not an official EN 2 fire class and must not be read as one.

Note: the lightning-bolt symbol on an extinguisher therefore says nothing about "which fire" it extinguishes — that remains class A/B/C/D/F — but it does indicate whether the extinguisher may safely be used while the installation may still be live.

The separate dielectric suitability test

In addition to the regular fire-class type approval, extinguishers that must be suitable for use on installations that may be live undergo a separate dielectric test, which demonstrates that the operator cannot receive a dangerous current back through the extinguishing jet at a given test voltage and distance. This has direct consequences for extinguisher selection:

• CO₂ extinguishers and powder extinguishers are inherently non-conductive and are generally considered safe for use on electrical installations, provided they are used at the correct distance.
• Water extinguishers and foam extinguishers are conductive in their basic form and are therefore not automatically suitable for use on an installation that may still be live — only a version explicitly dielectric-tested and certified for this purpose (identifiable by the marking on the extinguisher's nameplate, not by a pictogram) may be used.

Practical relevance

When assembling a firefighting-equipment plan for a space with electrical installations (switchgear room, server room, machine hall), it must be explicitly established whether the extinguishers present are approved for use on live parts — this is separate from the regular fire-class suitability (A/B/C/D/F) shown on the extinguisher label. An extinguisher that is perfectly suitable for a class A fire is not automatically also safe to use on a burning distribution board that may still be live.

Common mistakes

1. Assuming a "suitable for electrical equipment" sticker is an official EN 2 fire class — this is a separate voltage-suitability assessment, not a fire class E.
2. Placing a water or foam extinguisher near a switchboard without verifying that it is specifically dielectric-tested and certified for use on live installations.
3. Opening a burning distribution board directly to extinguish it — as also described in the arc flash guide, an arc can reignite when opened due to the sudden inrush of oxygen, regardless of which extinguishing agent is used.

Related

• Arc flash — causes and protection
• PV installations — fire service switch and DC marking (§712)
• Cables — fire classification (CPR)