Fire-Resistant Hydraulic Fluids (FRHF)

Fire Resistant Hydraulic Fluids

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Considering that mineral oils are highly combustible (flashpoint < 250oC), applications wherein hydraulic lines are in close proximity to open flames, sparks, very hot surfaces (> 200oC), or molten metal, should strongly consider the use of Fire-Resistant Hydraulic Fluids. While the hydraulic lines are typically enclosed, any damage to worn joints, seals, and hoses will cause an oil mist or leakage, increasing the fire risk.  Millions in losses are at stake:

» Production losses: production can be stopped for days

» Increased Health & Safety risks for operators

» Customers relationships: trust and supply reliability

fire resistant

Applications, where Fire-Resistant Hydraulic Fluids are recommended, includes die-casting, foundries, iron and steel-making, forging, mining, and power-plants.

Types of Fire-Resistant Hydraulic Fluids

There are three general classifications of FRHFs, with varying levels of fire-resistance as well as performance levels, lubrication-wise.

  • Oil and Water Emulsions
  • Water-Polymer Solutions
  • Anhydrous (Water-free) FRHFs

ISO further classifies these according to the table below:

Types of Fire-Resistant Hydraulic Fluids

Flammability and Fire-Resistance

It has to be made clear that Fire-Resistant Hydraulic Fluids DO NOT retard fire – when exposed to a hot-source, it will burn.  But unlike mineral oils that will propagate and increase combustion, FRHFs extinguishes the initial fire, allowing people ample time to re-locate to safer locations, and for assigned personnel to initiate fire-fighting activities.

FM logo

Factory Mutual (FM), an American mutual insurance company, tests lubricants and certifies their ‘fire-resistance’, according to a set of strict test-standards. When a product or service is stamped with the FM APPROVED certification mark, one knows that the lubricant has been tested and certified for fire-resistance.  This mark is globally recognized.

Note though that FM approvals DO NOT pertain to lubricating performance in any way.  We shall tackle the performance pros and cons of the different Fire-Resistant Hydraulic Fluids in a future segment.


Most FRHF’s are not miscible with mineral oils, and thus a careful and thorough flushing of the previous lubrication system is a must when one initiates an activity to convert to FRHFs. While the anhydrous fluids may be miscible with mineral oils to an extent, any trace mineral oil that contaminates the FRHF will certainly reduce fire-resistance properties, and therefore flushing is still recommended.

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