A class D fire extinguisher is a specialist extinguisher designed to suppress fires involving combustible metals such as magnesium, sodium, potassium, titanium, lithium, and zirconium.
Unlike ABC, CO₂, or foam extinguishers, a class D fire extinguisher uses a dry powder agent, sodium chloride, copper, or graphite based, matched to the specific metal, applied with a soft-flow technique to bury and smother the burning metal without scattering it. Standard fire extinguishers do not work on metal fires and can make them significantly worse.
This guide covers what a class D fire extinguisher is, the three agents it uses, how the discharge mechanism works, real sizing data, where this risk genuinely exists in Indian industry, the Indian standards position, and how to source one.
What is a class D fire extinguisher? direct definition
A class D fire extinguisher is a specialist extinguisher that uses dry powder agents, sodium chloride, copper, or graphite based, to suppress fires involving combustible metals such as magnesium, sodium, potassium, titanium, and lithium. It works by burying the burning metal under a heat-absorbing crust that excludes oxygen, applied gently through a soft-flow technique that avoids scattering burning metal particles.
A class D fire extinguisher is built for one job only: combustible metal fires, the rarest and most hazardous fire class encountered in industrial settings. It is not interchangeable with ABC, CO₂, foam, or wet chemical units, and it is not designed for general use. For the full chemistry of why standard extinguishers fail on metal fires. see our what is a class D fire guide.
The keyword that matters here is “metal fire extinguisher”. It is the plain-language way most people search for this product, and it describes exactly what a class D fire extinguisher does.
Why standard extinguishers don’t work on metal fires
The names “dry powder” and “dry chemical” sound almost identical. The products are entirely different, and confusing them in an emergency can be the difference between controlling a metal fire and watching it intensify.
“Dry chemical”, the agent inside the ABC fire extinguisher or BC extinguishers found in most Indian offices and factories, uses monoammonium phosphate or sodium bicarbonate. It works by interrupting the chemical chain reaction of an ordinary fire. On a metal fire burning above 1,000°C, and some metal fires exceeding 3,000°F (over 1,600°C), the dry chemical agent itself melts before it can perform its function.
That failure is dangerous precisely because it looks normal. The extinguisher discharges exactly as expected. The fire keeps burning as if nothing happened. Someone reaching for the nearest “powder extinguisher” without knowing the difference will grab the wrong one and only discover the failure once the metal fire does not respond.
CO₂ and water carry their own specific failures on metal fires. CO₂ can actively feed a burning magnesium fire, and water reacts violently with burning alkali metals such as sodium and potassium. The complete chemical equations behind both failures are covered in our what is a class D fire guide.
“Dry powder”, the genuine class D agent, whether sodium chloride, copper, or graphite based, is formulated specifically to remain stable at metal fire temperatures and form a protective crust over the burning metal, without reacting chemically with it. Any facility with combustible metal risk must label extinguishers clearly and train staff on this exact distinction.
The three class D extinguishing agents and which metal each one matches
Class D agents are not interchangeable with each other any more than they are interchangeable with ABC powder. Each agent is matched to a specific group of metals based on how it absorbs heat and excludes oxygen.
Sodium chloride based powder for magnesium, sodium and potassium
Sodium chloride (NaCl) based powder is the most widely available and most commonly specified class D fire extinguisher agent. When discharged onto a burning metal, the heat causes the powder to cake and fuse into a hard, heat-absorbing crust over the fire. This crust excludes oxygen and draws heat away from the metal, starving the reaction. It is the standard choice for magnesium, sodium, potassium, and sodium-potassium alloy fires.
Copper based powder for lithium metal specifically
Copper-based powder was developed originally by the US Navy for lithium metal fires and remains the standard agent for that purpose today. Copper’s high thermal conductivity rapidly draws heat away from the burning lithium, cooling it below ignition temperature faster than other agents can. Copper powder is matched specifically to lithium metal and lithium alloy fires, not to lithium-ion battery fires, which are a different hazard altogether and are covered separately below.
Graphite based powder for titanium, zirconium and aluminium
Graphite-based powder, often sold under names like G-Plus, is used for titanium, zirconium, and powdered aluminium fires, and for other high-temperature metal fires where sodium chloride’s performance becomes less reliable. Graphite remains stable at higher temperatures than sodium chloride, which makes it the preferred agent for these particular metals.
A fourth, less commonly discussed agent, Ternary Eutectic Chloride (TEC), is used in specialist aerospace contexts for specific magnesium and magnesium-alloy fires where standard sodium chloride performance is insufficient.
| Agent | Primary Metals | Mechanism | Notes |
|---|---|---|---|
| Sodium Chloride (NaCl) | Magnesium, sodium, potassium, Na-K alloy | Cakes into a heat-absorbing crust | Most widely available Class D agent |
| Copper Powder | Lithium metal, lithium alloys | High thermal conductivity rapidly cools the metal | Not for lithium-ion battery fires |
| Graphite Powder (G-Plus Type) | Titanium, zirconium, aluminium powder | Stable at higher temperatures than NaCl | Used for high-temperature metal fires |
| Ternary Eutectic Chloride (TEC) | Specific magnesium alloy applications | Aerospace-specific formulation | Specialist/aerospace context |
Lithium metal vs lithium-ion battery: a distinction that prevents a dangerous mistake
This distinction matters enormously given the growth of EV and battery manufacturing in India. Lithium metal fires, solid lithium metal used in primary batteries, chemical synthesis, and some battery research, are a genuine class D fire and respond to copper-based powder.
Lithium-ion battery fires are a fundamentally different hazard. They are caused by thermal runaway inside the cell, which generates its own internal oxygen supply. This makes smothering agents, including class D fire extinguisher powder, largely ineffective. Lithium-ion battery fires require a different response entirely, large-volume water immersion for small devices, or specialist agents such as F-500 or AVD for larger packs.
Anyone working in India’s growing EV and battery manufacturing sector needs to understand that these are not the same hazard, despite both involving the word “lithium,” and they do not share the same solution.
How a class D fire extinguisher works: the soft-flow technique
A class D fire extinguisher does not discharge like any other extinguisher type you have used. Understanding why matters before you ever need to use one.
Standard extinguishers, ABC, CO₂, foam, discharge under pressure, projecting the agent forcefully toward the fire through a nozzle. Class D fire extinguishers use a soft-flow or gravity-fed delivery system instead. The agent is released gently, typically through a wide applicator held close to the burning metal, so the powder settles by gravity rather than being sprayed.
This matters because a forceful discharge on burning metal chips, shavings, or powder scatters the burning particles across a wider area. Each scattered particle becomes a new ignition point, and the fire footprint expands instead of shrinking. The soft-flow design exists specifically to prevent this. The extension applicator found on most class Dfire extinguisher units lets the operator stand back from intense heat and toxic fumes while still applying the agent gently rather than blasting it from close range.
Before attempting to use a class D fire extinguisher, check that you can lift and carry it safely to the fire. This is not a formality. It is a genuine operational safety step specific to class D response. Larger units, 30lb and above, require two people or should be left to trained emergency responders. This check matters particularly for smaller Indian facilities, where a single junior staff member might otherwise attempt to use a heavy trolley-mounted unit alone.
Class D fire extinguisher sizes and weight capacities
Class D fire extinguisher units come in a wider range of sizes than most Indian buyers expect, driven by how much agent is needed to fully bury a metal fire.
Portable units typically range from 18 to 30lb, roughly 8 to 14kg. Wheeled or trolley-mounted units are significantly larger, 125lb, 150lb, and up to 250lb, roughly 57kg, 68kg, and 113kg, for high-volume industrial applications such as foundries and large metal processing facilities.
| Type | Typical Capacity | Approx. Weight (kg) | Application |
|---|---|---|---|
| Portable | 18 to 30 lb | 8 to 14 kg | Small workshop, lab, light industrial |
| Wheeled / Trolley | 125 lb | 57 kg | Medium industrial, foundry |
| Wheeled / Trolley | 150 lb | 68 kg | Larger industrial facilities |
| Wheeled / Trolley | 250 lb | 113 kg | Heavy industrial, large foundries |
For Indian buyers used to ABC sizing, a 30lb (roughly 14kg) class D fire extinguisher portable unit is substantially heavier than the common 9kg ABC unit found in most Indian commercial buildings. That extra weight reflects the larger volume of agent needed to bury and smother a metal fire, compared with the smaller quantity needed to knock down a class A, B, or C flame.
Where class D fire risk actually exists in India
Class D fire risk is not present in a typical Indian office, home, restaurant, or general commercial building. It is specific to facilities that machine, process, or synthesise combustible metals in a form that increases surface area, chips, swarf, dust, or fine powder, not solid stock.
Aerospace and defence manufacturing. Magnesium alloy components and titanium structural parts and fasteners are common across DRDO, HAL, and private aerospace component manufacturers, particularly during machining operations.
Automotive die-casting. Magnesium alloy die castings are increasingly used for engine components, gearbox housings, and structural parts as Indian automotive manufacturers, including Maruti Suzuki, Tata, Mahindra, and their tier-1 suppliers, pursue weight reduction. The real class D risk arises during machining and finishing, where swarf, chips, and fine dust are generated.
Pharmaceutical API manufacturing. Sodium metal and potassium metal are used as reagents in organic synthesis reactions for active pharmaceutical ingredient production, making this a genuine and ongoing class D risk across India’s large pharmaceutical manufacturing sector.
Metallurgical and material science research. Academic institutions and CSIR laboratories working with reactive metals carry the same risk profile on a smaller scale.
If your facility does not machine, grind, cut, or synthesise with magnesium, titanium, sodium, potassium, lithium, or zirconium, class D risk likely does not apply to you. If it does, the next step is a formal combustible metal fire risk assessment.
No dedicated IS standard for class D agents: what Indian buyers need to know
Unlike ABC powder, which is governed by IS 14609, or portable extinguishers generally under IS 15683:2018, there is currently no widely adopted, dedicated Indian Standard specifically governing class D dry powder agent performance. IS 2190:2010, which covers the selection, installation, and maintenance of fire extinguishers, references class D fires and the need for specialist agents, but it does not provide the detailed performance specification that exists for ABC and CO₂ fire extinguisher agents.
In practice, this means class D fire extinguisher agents available in India and used by industrial facilities are typically certified against international references, UL listings for specific metal applications, or manufacturer-specific test data demonstrating effectiveness on named metals such as magnesium, sodium, or titanium. NFPA 484, the US standard covering combustible metals, is frequently used as a technical reference point in this gap.
When procuring a class D fire extinguisher for an Indian facility, verify the agent’s metal-specific test certification directly with the supplier, rather than relying on an ISI Mark equivalent. That specific dedicated mark does not currently exist for class D agents in the same form it does for ABC powder.
Sand as an emergency alternative: when no class D fire extinguisher is available
When a proper class D fire extinguisher is not available and a small metal fire occurs, dry sand can be applied as an emergency interim measure to cover and smother the fire.
The sand must be completely dry. Any moisture in the sand reacts with burning alkali metals such as sodium and potassium exactly as water does, producing hydrogen gas and worsening the fire. Apply the sand by gently covering the burning metal, not by pouring it forcefully, to avoid scattering burning particles in the same way a forceful extinguisher discharge would.
Sand is an interim measure only. It is not a substitute for proper class D fire protection in any facility with ongoing combustible metal risk. Any facility identified as having genuine class D risk should have a correctly specified class D fire extinguisher in place, not rely on sand as the primary response plan.
How to source a class D fire extinguisher in India
Class D fire extinguishers are a specialist, lower-volume product in the Indian fire safety market compared with ABC, CO₂, foam, or wet chemical units. They are not typically stocked as standard inventory by general fire safety retailers, and most mainstream Indian suppliers carry ABC, CO₂, foam, and wet chemical as their default range.
For Indian facilities with confirmed class D risk, the practical path looks like this:
- Complete a combustible metal fire risk assessment, identify the specific metals present, their physical form (solid stock versus chips, dust, or powder), and the quantity involved.
- Match the agent type to the metal using the table above, sodium chloride, copper, or graphite based.
- Source from a manufacturer experienced in industrial and specialist fire safety equipment who can provide metal-specific test certification.
- Specify portable or wheeled capacity based on facility scale and the volume of metal stock or process material on site.
Speciality Geochem advises Indian industrial, aerospace, and pharmaceutical clients on combustible metal fire risk assessment and on correctly specifying class D protection for their facility, alongside our manufactured range of ABC, CO₂, and foam extinguishers. For facility-specific guidance, get in touch with our team directly.
Class D fire extinguisher vs ABC, CO₂ and other types
| Feature | ABC Dry Powder | CO₂ | Class D |
|---|---|---|---|
| Fire Classes | A, B, C, E | B, C, E | D only |
| Agent | Monoammonium phosphate | Carbon dioxide gas | NaCl, copper, or graphite |
| Discharge | Forceful spray | Gas / snow | Soft-flow / gravity |
| On Metal Fires | Fails, melts at fire temperature | Fails, can feed magnesium fires | Only correct choice |
| Availability in India | Widely available | Widely available | Specialist / special-order |
| Typical Environments | Home, office, general commercial | Server rooms, electrical | Aerospace, die-casting, pharma synthesis |
For the complete guide to all fire extinguisher types used in India, see our types of fire extinguisher in India guide.
Frequently asked questions: class D fire extinguisher
What is a class D fire extinguisher?
A class D fire extinguisher is a specialist extinguisher that uses dry powder agents, sodium chloride, copper, or graphite based, to suppress fires involving combustible metals such as magnesium, sodium, potassium, titanium, and lithium. It is not used for ordinary fires and is not interchangeable with ABC, CO₂, or foam fire extinguisher units.
What agent is inside a class D fire extinguisher?
Most class D fire extinguishers use one of three agents: sodium chloride powder for magnesium, sodium, and potassium; copper powder for lithium metal; or graphite-based powder for titanium, zirconium, and aluminium. A specialist agent called Ternary Eutectic Chloride is also used in some aerospace magnesium applications.
Why doesn’t an ABC fire extinguisher work on metal fires?
ABC powder uses monoammonium phosphate, which melts at metal fire temperatures that can exceed 3,000°F (over 1,600°C). The extinguisher discharges normally but the agent fails to suppress the fire, which keeps burning as if nothing happened.
What is the difference between dry chemical and dry powder extinguisher?
“Dry chemical” refers to ABC or BC agents designed for ordinary, flammable liquid, and electrical fires. “Dry powder” refers specifically to class D metal fire agents, sodium chloride, copper, or graphite based. The names sound similar, but the products are not interchangeable and using the wrong one on a metal fire causes complete failure.
How does a class D fire extinguisher work?
It works by depositing a dry powder agent gently over the burning metal using a soft-flow technique. The agent forms a heat-absorbing crust that excludes oxygen and cools the metal below its ignition temperature, smothering the fire without scattering burning particles.
Why does a class D fire extinguisher discharge differently from other extinguishers?
Other extinguishers discharge forcefully through a nozzle. A class D fire extinguisher uses a soft-flow or gravity-fed system because forceful discharge on burning metal chips or powder scatters the particles, creating new ignition points and spreading the fire instead of containing it.
Which agent should be used for a lithium metal fire?
Copper-based powder is the standard agent for lithium metal fires. It was originally developed by the US Navy specifically for this purpose and works by rapidly conducting heat away from the burning lithium.
Which agent should be used for a magnesium fire?
Sodium chloride based powder is the standard agent for magnesium fires. It cakes into a hard crust over the burning metal that excludes oxygen and absorbs heat. Ternary Eutectic Chloride is used for some specialist magnesium alloy applications in aerospace settings.
Can copper powder be used on lithium-ion battery fires?
No. Copper powder is matched to lithium metal fires, not lithium-ion battery fires. Battery fires involve thermal runaway that generates its own oxygen supply internally, which makes copper powder and other smothering agents largely ineffective. Battery fires need a different response, such as large-volume water immersion or specialist agents like F-500 or AVD.
What is the difference between a lithium metal fire and a lithium-ion battery fire?
A lithium metal fire involves solid lithium metal burning directly and responds to copper-based class D fire extinguisher powder. A lithium-ion battery fire is caused by internal thermal runaway that generates its own oxygen, making it a fundamentally different hazard that class D agents cannot reliably extinguish.
What metals require a class D extinguisher?
The metals most commonly requiring class D protection are magnesium, sodium, potassium, titanium, lithium, zirconium, and powdered aluminium. The correct agent depends on which metal is present.
What weight do class D extinguishers come in?
Portable class D fire extinguisher units typically range from 18 to 30lb (roughly 8 to 14kg). Wheeled or trolley-mounted units range from 125lb to 250lb (roughly 57kg to 113kg) for larger industrial applications such as foundries.
Is there an Indian standard (IS) for class D extinguishers?
There is no dedicated, widely adopted Indian Standard specifically governing class D dry powder agent performance. IS 2190:2010 references class D fires and the need for specialist agents, but detailed agent performance specifications largely follow international references such as NFPA 484 and UL listings.
Where is class D fire risk found in Indian industry?
Class D risk in India is concentrated in aerospace and defence manufacturing, automotive die-casting involving magnesium alloys, pharmaceutical API synthesis using sodium or potassium metal, and metallurgical or material science research handling reactive metals.
Can sand be used on a metal fire if no class D fire extinguisher is available?
Yes, as an emergency interim measure only. The sand must be completely dry, since any moisture reacts with burning alkali metals like sodium and potassium and produces hydrogen gas. Sand should be applied by gently covering the fire, not poured forcefully.
How do I check before using a class D fire extinguisher?
Before attempting to use one, check that you can lift and carry it safely to the fire. Larger units, 30lb and above, require two people or should be left to trained emergency responders rather than attempted by a single person.
Are class D fire extinguishers commonly available in India?
No. They are a specialist, lower-volume product compared with ABC, CO₂, foam, or wet chemical extinguishers, and are not typically stocked as standard inventory by general Indian fire safety retailers. They are usually supplied as a special-order or project-specific item.
What is Ternary Eutectic Chloride (TEC) and when is it used?
Ternary Eutectic Chloride is a specialist class D agent used mainly in aerospace contexts for specific magnesium and magnesium-alloy fires where standard sodium chloride performance is insufficient.
Can CO₂ be used on a metal fire?
No. CO₂ is ineffective on most metal fires and can actively feed certain reactions, including magnesium fires, making the fire worse rather than suppressing it.
What is the difference between a class D fire extinguisher and an ABC fire extinguisher?
An ABC extinguisher uses monoammonium phosphate for fires involving ordinary combustibles, flammable liquids, and electrical equipment, and it fails on metal fires because the agent melts at metal fire temperatures. A class D fire extinguisher uses sodium chloride, copper, or graphite based powder specifically formulated to remain stable and smother burning metal, and it is the only correct choice for combustible metal fires.
The bottom line
Class D fire extinguishers are specialist equipment for a specific and narrow set of industrial risks. They are not something every Indian facility needs, and pretending otherwise would be dishonest. But for the facilities that do machine, process, or synthesise with combustible metals, having the correctly matched agent, in the right quantity, sourced from a supplier who understands the metal-specific requirements, is not optional.
Speciality Geochem advises Indian industrial, aerospace, and pharmaceutical clients on combustible metal fire risk assessment and correct class D fire extinguisher specification. For facility-specific guidance, contact Speciality Geochem directly. For the chemistry behind why metal fires are uniquely dangerous, see class D fire guide.