Is hydraulic oil flammable? The short answer is yes...most hydraulic oils can burn. The more nuanced explanation is that each type of hydraulic fluid has unique fire characteristics, which makes sense — hydraulic systems are found in all manner of heavy equipment and applications, from skid steers and excavators to manufacturing and agricultural machinery.
To balance safety and performance as you select your fluid, you’ve got to take stock of the demands on the equipment and understand the flammability risks that come with them.
Standard hydraulic oil is made from mineral oil, which is derived from petroleum. In other words, it comes from oil — the same substance we burn in all sorts of fossil fuel applications. Naturally, it’s flammable.
Hydraulic oil products are necessary for the safe and smooth operation of hydraulic systems, but they can ignite if exposed to enough heat or an ignition source. They are also considered “combustible,” meaning they can sustain combustion under the right conditions.
That doesn't mean every hydraulic system presents the same fire risk. The greatest common concern is when a high-pressure leak sprays fluid onto hot engine components, exhaust systems, or open flames. Oil stored in a container or reservoir is not typically a big risk.
Still, the level of flammability varies by type:
Mineral based hydraulic oil remains the most common hydraulic fluid. It offers reliable industrial lubrication along with broad equipment compatibility — all at an attractive lower cost than other options.
It's also the most flammable category. However, for most construction equipment, farm machinery, and industrial hydraulic systems, that's perfectly acceptable. If operating conditions don't justify a specialty fluid, you can save on costs. If you keep up with maintenance and cleaning of hydraulic systems, you’ll also keep fire risk to a minimum.
Water-based hydraulic fluids are the least likely to ignite because much of the fluid is water. Water-glycol formulations are selected most often at steel mills, foundries, mining operations, and similar environments where hydraulic systems have to operate close to extreme heat or molten materials.
While these fluids improve fire resistance, they aren't a universal replacement. Always review equipment compatibility and operating requirements before making a change.
Synthetic hydraulic fluids cover a pretty broad range of chemistries. Some are formulated specifically for improved fire resistance, while others are chosen for traits like temperature stability, longer service life, or demanding operating conditions.
The same is true for biodegradable hydraulic oil. Many biodegradable fluids are designed to reduce environmental impact if leaks occur — great in environmentally sensitive applications like forestry and marine work. Some biodegradable formulas also offer improved fire resistance, but others remain combustible despite their environmental benefits.
Fire resistance, ultimately, will vary by the specific synthetic or biodegradable product. One fluid shouldn't be assumed to behave like another (and it’s best not to mix hydraulic fluids). Double check manufacturer info and specs.
These two terms cause plenty of confusion. Let’s clear it up.
Hydraulic fluids are not fireproof. Equipment manufacturers do specify fire resistant fluids for high heat applications — steel production, power generation, mining, die casting, etc. — because hydraulic leaks could contact intense heat.
However, flammability is only one factor in your choice of hydraulic fluid. Manufacturer or service personnel recommendations must consider:
…among other things. It doesn’t matter whether you're using conventional mineral oil, a specialty synthetic product, or biodegradable hydraulic oil. The fluid has to match the application to protect both equipment and the people working around it.
Are you unsure which hydraulic oil fits your equipment or operating environment? A Certified Lubrication Specialist at Whatley Oil can help you compare products and choose a hydraulic fluid that meets your performance and safety requirements. Give us a call!