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.

What EN 3-7 actually specifies

The dielectric suitability of a portable extinguisher is tested under EN 3-7. Extinguishers that pass may be marked as suitable for use on live installations up to 1000 V at a distance of at least 1 metre (the usual "1000 V / 1 m" marking). Note the limits:

the value applies to low voltage; on medium or high voltage you do not fight the fire with a portable extinguisher — you isolate, or wait for the fire brigade;
it is a manufacturer's marking after testing, not a general property of the agent — check the nameplate and documentation;
the 1 m distance must actually be kept while extinguishing; with a DC source (PV, battery) you cannot switch off, the installation stays live even after "switching off".

(Do not confuse with IEC 61243: that is the standard for voltage detectors, not for extinguishers.)

Lithium-ion fires are a special case

A fire in a lithium-ion battery (energy storage, UPS, e-bike, EV) is not an ordinary fire: through thermal runaway the cell can keep heating itself, reignite hours later and release toxic gases (including hydrogen fluoride). An ordinary powder or CO₂ extinguisher knocks down the flame but does not cool the cell. EN 3-11 exists for this: additional requirements and tests on top of EN 3-7 for extinguishers suited to fires in small Li-ion batteries (up to about 600 Wh, e.g. e-bike or laptop batteries). For a larger battery (container, rack, UPS room): leave the room, close the door, call 112, do not fight it with a portable extinguisher, and tell the fire brigade the battery type. See also the guides on lithium BMS and UPS.

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

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.
Placing a water or foam extinguisher near a switchboard without verifying that it is specifically dielectric-tested and certified for use on live installations.
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.