Ansul LITH-X vs. MET-L-X: Which Class D Agent Do You Actually Need?

Last updated: August 10, 2026

If you work with combustible metals and you know you need a Class D extinguisher, you've almost certainly run into both of these names. LITH-X and MET-L-X are both Ansul Class D dry powder agents, they look similar, they're both applied the same way, and they're often stocked side by side. They are not interchangeable.

Choosing the wrong one for your specific metal fire risk isn't a minor inconvenience. It's the difference between an agent that works and one that doesn't, and in a Class D fire situation, that gap matters more than almost anywhere else in fire protection.

At Pro Fire and Safety, we believe the right agent starts with understanding what's actually burning. Here's exactly how LITH-X and MET-L-X differ, which metals each one covers, and the one critical distinction about LITH-X that trips up even experienced buyers.

Why Class D Is Its Own Category

Before getting into the two agents, it's worth grounding why Class D fires require their own agents in the first place, because it explains why neither of these products looks or works anything like a standard dry chemical extinguisher.

Combustible metals like magnesium, sodium, potassium, and lithium burn at extremely high temperatures, often well above what standard agents are designed to handle. More importantly, several of these metals react dangerously with water, making water-based suppression not just ineffective but actively hazardous. Standard dry chemical agents can also react unpredictably with burning metals in ways that intensify rather than suppress the fire.

Class D agents work on a fundamentally different principle: they smother, insulate, and in some cases conduct heat away from the burning mass rather than chemically interrupting the combustion reaction the way standard agents do. That's why both LITH-X and MET-L-X are dry powders applied in a thick layer over the burning material, not discharged from a distance the way a standard extinguisher is used.

MET-L-X: The Salt-Crust Agent

English: The "melt, seal, and smother" agent.

MET-L-X is a dry powder composed of a salt base plus a polymer for sealing, and other additives to render it free-flowing and cause heat caking or crusting.

When MET-L-X is applied to a burning metal, the heat from the fire melts the sodium chloride base, forming a dense, oxygen-excluding crust over the burning material. That crust physically seals the metal from the surrounding air, smothering the fire by denying it oxygen. The polymer component helps the crust hold together and adhere to the burning surface.

MET-L-X is listed by Underwriters Laboratories for use on sodium, potassium, sodium-potassium alloy (NaK), and magnesium alloys. It will also control and sometimes extinguish small fires on zirconium and titanium.

In practical terms, MET-L-X is the agent for metal shops, foundries, and industrial facilities where magnesium, sodium, or potassium are the primary hazards. It's also available in a wide range of sizes, from hand-portable units through wheeled and stationary extinguishers, and can be discharged through hose lines for larger quantities. For small, contained incidents, many people apply this agent with a scoop or shovel.

One thing to know about MET-L-X before specifying it: the salt base that makes it effective at crust formation also means it's corrosive to stainless steel over time. Sodium carbonate-based agents like Na-X are preferred where stainless steel piping and equipment could be damaged by sodium chloride based agents, particularly on sodium, potassium, and NaK fires in environments where equipment contamination is a concern.

LITH-X: The Graphite-Heat-Sink Agent

English: The "exclude air, conduct heat away" agent.

LITH-X is a compound of a special graphite base with additives to render it free-flowing. It does not cake or crust, but excludes air and conducts heat away from the burning mass to extinguish the fire.

This is the core mechanical difference between the two agents. Where MET-L-X forms a solid crust over the burning material, LITH-X works by blanketing the fire in graphite powder that simultaneously blocks oxygen and acts as a heat sink, pulling thermal energy away from the burning mass. The graphite doesn't melt or form a crust. It stays as a powder layer that smothers and cools at the same time.

LITH-X was developed for use on lithium fires, and will also extinguish magnesium, sodium, and potassium fires. LITH-X will contain, and in some cases completely extinguish, fires of zirconium, titanium, and sodium-potassium alloy.

On paper, LITH-X covers more metals than MET-L-X does. In practice, it's specified primarily for facilities that work with metallic lithium: battery research labs, military and aerospace applications, and certain chemical manufacturing environments where lithium metal is present as a raw material or process component.

The Most Important Distinction About LITH-X

This is the point that causes the most confusion in the market right now, and it's worth being direct about it.

LITH-X is suitable for lithium metal batteries (disposable, single-use batteries only), not for lithium-ion rechargeable batteries commonly found in laptops, phones, and power tools.

This matters enormously right now because "lithium fire" has become a shorthand in the market that covers two completely different things. Lithium metal batteries are non-rechargeable primary batteries that contain metallic lithium as the anode. Lithium-ion batteries are rechargeable and contain no metallic lithium in the anode. These are different chemistries, different fire mechanisms, and they require different suppression approaches.

The e-bike battery, the phone battery, the EV battery pack, and the power tool battery in your shop are all lithium-ion, not lithium metal. LITH-X is not the answer for those fires. For lithium-ion battery fires, the correct portable suppression option is an AVD-type agent, like the Victory 6L AVD covered separately on this blog.

LITH-X is the answer when you're working with raw metallic lithium: research environments, battery manufacturing facilities that handle lithium metal before it becomes a finished cell, or military and aerospace applications where primary lithium batteries are in use.

Side by Side

Which One Do You Need?

The answer comes down to what metal is actually present in your facility.

Specify MET-L-X if: your primary hazard is magnesium, sodium, potassium, or NaK in a machining, foundry, or industrial chemical environment. It's the more broadly available agent, comes in a wider range of delivery formats, and is the standard choice for most industrial metal fire hazards.

Specify LITH-X if: your facility handles raw metallic lithium, whether in a research context, a battery manufacturing process, or a military/aerospace application involving primary lithium cells. It was developed specifically for this hazard and its graphite mechanism is better suited to lithium metal's specific burn characteristics.

Specify neither if: your concern is lithium-ion battery fires from rechargeable devices, e-bikes, EVs, or energy storage systems. Neither of these agents is the right tool for that problem.

For the Professionals

When customers come in asking for "a lithium extinguisher," the first question worth asking is whether they mean lithium metal or lithium-ion, because the answer sends them toward completely different products. This confusion is increasingly common as lithium-ion battery fires get more media coverage and customers assume any agent with "lith" in the name covers their e-bike shop or warehouse charging station.

Getting this right matters for liability as much as it does for fire protection outcomes. Both MET-L-X and LITH-X are available through HedrickPro in pail quantities for contractors and facilities that stock Class D agents as part of a broader hazard assessment.

Keep It Simple

MET-L-X uses a salt-crust mechanism for magnesium, sodium, potassium, and NaK fires. LITH-X uses a graphite heat-sink mechanism developed specifically for metallic lithium. Neither is appropriate for lithium-ion battery fires. Know which metal is actually present in your facility, and specify the agent that was built for it.

Not sure which Class D agent fits your specific metal hazard, or need help assessing whether your current setup covers what's actually in your facility? Shop our full line of Class D extinguishers and agents today, or contact us if you want a straight answer on what your situation actually calls for. At Pro Fire and Safety, the right agent is the one that matches the metal, not just the label.

Reviewed by Joseph Hedrick, NFPA-certified fire protection specialist