Class 4.3 - Substances That Emit Flammable Gases When in Contact with Water

The final division within Class 4, Flammable Solids is Class 4.3, Substances Which, in Contact with Water, Emit Flammable Gases. The substances in this group are either liquids or solids that are likely to become flammable or to give off flammable gases when they interact with water. This can lead to explosions and fires dangerous to both people and the environment. The gases are easily ignitable by ordinary sources of ignition such as sparks from unprotected lights or hand tools. Three packing groups with the designations I, II, or III are assigned to these substances. Packing group I is assigned to the most dangerous and reactive substances in the group. One subset of this type of substance is organometallics. These may be classified under Class 4.2 or 4.3 depending on the particular substances characteristics. A decision flowchart is provided under Section 2.4.5 to guide the classification of these substances.

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