Specification for a dry powder fire extinguisher for metal fires
1986 Edition

The materials specified for dry powder metal fire extinguishers under IS 11833 include: the body and shell made from mild steel plates and seamless mild steel tubes; discharge fittings crafted from leaded tin bronze (Grade LTB-2) or extruded brass; discharge nozzles composed of aluminum alloy, extruded brass, or leaded tin bronze; expellant gas cylinders constructed from mild steel tubes or manganese steel; and hoses made of braided rubber or plastic designed to withstand bursting pressures of at least 50 kgf/cm². This selection ensures the extinguishers are durable, corrosion-resistant, and capable of safely containing pressure suitable for metal fire applications.

IS 11833 mandates that the minimum dry powder content in a metal fire extinguisher corresponds exactly to its nominal capacity. For example, a 10 kg extinguisher must contain at least 10 kg of dry powder, a 25 kg unit must have 25 kg, and so forth up to 100 kg. Additionally, the extinguisher must discharge no less than 85% by mass of this rated capacity under test conditions (27 ± 2°C). Discharge durations vary with size, ranging from 20–30 seconds for 10 kg units to 70–80 seconds for 100 kg models, with internal pressure limits maintained to ensure safety and effectiveness.

Per IS 11833 Clause 8.1, the applicator is engineered for secure and effective powder deployment on metal fires by incorporating an extended pipe of minimum 1 meter length, allowing operators to maintain a safe distance from the reactive fire. The pipe terminates with a dome-shaped bell fitted with deflecting vanes that disperse the dry powder as a low-pressure spray uniformly across the burning metal surface. This approach minimizes disturbance of the fire and prevents scattering of burning materials, providing controlled and efficient fire suppression while ensuring operator safety.

IS 11833 strictly prohibits the inclusion of any ozone-depleting substances (ODS) recognized under the Montreal Protocol within dry powder metal fire extinguishers. Examples of banned substances include Halon 1211, Halon 1301, CFC-11, and methyl bromide, among others listed in Annex A. Furthermore, coatings on metallic parts must exclude mercury and its compounds, as well as pigments containing lead, cadmium, and chromium VI or their oxides, except for natural impurities not exceeding 0.1% by weight. These regulations aim to safeguard environmental health and reduce toxic exposure risks.

Under IS 11833, dry powder metal fire extinguishers are required to undergo discharge testing at 27 ± 2°C in still air conditions. The extinguisher, operated with its applicator, must release at least 85% of its rated dry powder mass. The discharge duration is specified according to capacity, ranging from 20–30 seconds for 10 kg extinguishers up to 70–80 seconds for 100 kg models. The discharge must be a steady, low-pressure stream to ensure effective fire suppression and operator safety. Passing these tests confirms the extinguisher’s operational reliability and suitability for metal fire emergencies.