Is Hydraulic Oil Flammable?

Is Hydraulic Oil Flammable?

Yes—hydraulic oil can burn. Most standard hydraulic oils (especially mineral/petroleum-based oils) are combustible, meaning they can ignite when exposed to enough heat, a flame, or a spark. The risk increases significantly if hydraulic oil is released as a fine spray or mist from a high-pressure leak and contacts a hot surface.

Hydraulic oil usually does not ignite easily at room temperature, but real hydraulic systems often operate under conditions where ignition becomes possible—high temperatures, high pressure, hot equipment surfaces, and potential leaks.

Short Answer

Hydraulic oil is flammable in the sense that it can ignite and burn.

Most hydraulic oils are not as easy to ignite as gasoline, but they can catch fire in the presence of heat, sparks, flames, or hot surfaces—especially if oil is sprayed or atomized into a mist.

Why Hydraulic Oil Can Catch Fire

Hydraulic oil becomes a fire hazard when these conditions come together:

  • Heat (hot components, high operating temperatures)
  • Ignition source (sparks, flames, electrical arcing)
  • Fuel exposure (oil on surfaces, dripping oil, or sprayed oil mist)
  • Air/oxygen (oil mist mixes with air more easily than pooled oil)

A puddle of hydraulic oil may not ignite quickly, but oil that is sprayed into the air can ignite much more easily.

Flammable vs Combustible (Simple Explanation)

People often use “flammable” as a general term, but many hydraulic oils are technically combustible.

  • Flammable liquids ignite at relatively low temperatures.
  • Combustible liquids require higher temperatures to ignite.

Combustible does not mean safe.
It only means the oil usually needs more heat before ignition is likely.

The 3 Temperatures That Matter Most

When evaluating fire risk, these temperature terms are important:

Flash Point

The flash point is the temperature where a fluid can produce enough vapor to ignite briefly when exposed to a spark or flame.

Fire Point

The fire point is the temperature where a fluid can ignite and continue burning after it is lit.

Autoignition Temperature

The autoignition temperature is the temperature where a fluid can ignite without a spark or flame.

Real-world fire risk increases when hydraulic oil is heated, sprayed, or exposed to high-temperature surfaces in operating equipment.

The Biggest Real-World Risk: Oil Mist From High-Pressure Leaks

One of the most dangerous hydraulic fire scenarios is a high-pressure leak that creates a fine oil mist.

Oil mist is more likely to ignite because:

  • It has far more surface area exposed to oxygen
  • It mixes with the air easily
  • It can travel and contact ignition sources quickly
  • It can ignite rapidly when it hits hot components

This is why small pinhole leaks and spray leaks should always be treated as urgent safety hazards.

Can Hydraulic Oil Ignite on a Hot Engine or Exhaust?

Yes. Hydraulic oil can ignite if it contacts hot surfaces, such as:

  • Engine components
  • Exhaust systems
  • Turbochargers
  • Heaters
  • Hot bearings
  • Industrial equipment with high surface temperatures

Even if the oil does not ignite immediately, it can produce smoke, smolder, or ignite as temperatures rise.

Is AW Hydraulic Oil (Like AW-46) Flammable?

Most AW hydraulic oils (such as AW-32, AW-46, and AW-68) are petroleum-based mineral oils with additives for wear protection.

That means:

  • They are combustible
  • They can ignite and burn
  • They can become a serious fire hazard in systems with heat, leaks, or oil misting

They are not “non-flammable” fluids.

What Increases the Risk of a Hydraulic Oil Fire?

Hydraulic oil fire risk increases when any of the following conditions exist:

  • Aging hoses (cracks, abrasion, weakness)
  • Loose or damaged fittings
  • High operating temperatures
  • Oil leaking onto hot surfaces
  • Oil buildup on equipment
  • Welding or grinding near hydraulic components
  • Electrical arcing near oil residue
  • Poor ventilation around heated equipment

In many cases, hydraulic fires are caused by a combination of high pressure + a leak + heat.

Hydraulic Fluid vs Hydraulic Oil (Are They the Same?)

Hydraulic fluid is a broad term that includes many types of fluids used in hydraulic systems.

Hydraulic oil commonly refers to mineral/petroleum-based fluids, but hydraulic fluid can also include:

  • Water-based fluids
  • Water-glycol fluids
  • Synthetic fluids
  • Fire-resistant hydraulic fluids

Fire behavior and safety risk can vary depending on the type of hydraulic fluid being used.

What Are Fire-Resistant Hydraulic Fluids?

In higher-risk environments, fire-resistant hydraulic fluids may be used to reduce ignition risk. Common categories include:

Water-Glycol Fluids

Often used in areas where fire safety is a priority. They can reduce ignition risk compared to mineral oil, but may require careful attention to system compatibility.

Water-Based Emulsions

Some fluids use high water content to lower the chance of ignition. These are typically used in specific applications where fire resistance matters.

Synthetic Fire-Resistant Fluids

Some synthetic hydraulic fluids provide improved fire resistance, especially in high-temperature or ignition-prone environments. Compatibility with seals and system materials should always be verified before switching.

Fire-resistant does not mean fire-proof. These fluids reduce risk, but they do not eliminate it.

Hydraulic Oil Fire Prevention Checklist

Most hydraulic oil fires are preventable with basic maintenance and safe practices.

Leak Prevention and Control

  • Inspect hoses and fittings regularly
  • Repair small leaks before they become spray leaks
  • Replace worn hoses, especially in high-flex or high-heat areas
  • Tighten or replace damaged fittings

Heat Management

  • Route hoses away from hot surfaces
  • Use heat shields near exhaust or heaters
  • Keep coolers and airflow paths clean and functional
  • Avoid overheating caused by low fluid levels or restricted flow

Cleanliness and Housekeeping

  • Clean oil residue from equipment surfaces
  • Remove oil-soaked debris and rags from work areas
  • Keep spill absorbent material nearby
  • Prevent buildup of oily grime around hot components

Safe Work Practices

  • Avoid welding or grinding near hydraulic leaks or oil residue
  • Shut down and depressurize systems before repairs
  • Treat misting leaks as urgent hazards
  • Train personnel to recognize high-pressure spray risks

What To Do If You Suspect a Leak Near Heat

If you notice smoke, an oil smell, or visible misting spray:

  • Shut the equipment down safely
  • Keep people away from the area
  • Do not touch the leak
  • Allow the system to cool
  • Repair the leak and clean oil residue before restarting

A small leak can turn into a larger hazard quickly, especially once temperatures rise again during normal operation.

Signs Hydraulic Oil May Be Overheating

Overheated hydraulic oil increases breakdown, leak risk, and fire potential. Common warning signs include:

  • Burnt or sharp oil odor
  • Darkened oil color
  • Sluggish system performance when hot
  • Unusual noise from the pump or valves
  • Foaming or aeration in the reservoir
  • Repeated seal or hose failures
  • Unusually high operating temperatures

If overheating is consistent, the system should be inspected for causes such as restricted cooling, contamination, improper fluid type, low fluid levels, or component wear.

FAQ

Is hydraulic oil flammable at room temperature?

Hydraulic oil typically does not ignite easily at room temperature, but it can burn when exposed to a flame or spark. Fire risk increases with heat and misting leaks.

Can hydraulic oil ignite without a flame?

Under extreme temperatures, hydraulic oil can ignite without a flame if it reaches its autoignition temperature. This risk is higher when oil is atomized or exposed to very hot surfaces.

Why is oil mist more dangerous than a spill?

Oil mist mixes with air and has far greater surface area exposure, making it more likely to ignite quickly—especially if it contacts a hot surface.

Are all hydraulic fluids flammable?

No. Some hydraulic fluids are designed to be fire-resistant. However, many common mineral oil-based hydraulic fluids can ignite and burn under the right conditions.

Does fire-resistant hydraulic fluid mean it cannot burn?

No. Fire-resistant fluids reduce ignition risk, but they can still burn under severe conditions.

Bottom Line

Hydraulic oil can burn. Most standard hydraulic oils are combustible and can ignite when exposed to heat, sparks, flames, or hot surfaces—especially when released as a mist from a high-pressure leak.

Preventing fires comes down to the basics: control leaks, manage heat, keep equipment clean, and treat spray leaks as urgent safety hazards.