Hyd Fluid And Fire
Joined: Dec 2004
Posts: 733
Likes: 2
From: Andalucia
from www.skydrol.com where there is a wealth of information :
Q: Are Skydrol hydraulic fluids fire-proof? A: No. There are conditions under which Skydrol will burn. Skydrol fluids are "fire resistant." Traditionally the term "fire resistant" has been used to describe phosphate esters, as opposed to mineral oil based hydraulic fluids, because they are very difficult to ignite at room temperature. In standardized testing, a fine mist spray of Skydrol cannot be ignited with a burning propane torch. The same fine mist spray of a mineral oil hydraulic fluid, such as MIL-H-5606 or MIL-PRF-83282, produces a large fireball when touched by a propane torch.
The basic parameters of fire resistance include: 1) resistance to ignition, and 2) resistance to propagation of the flame from the source of ignition. The test methods followed by the industry are described in AMS 3150 and various ASTM test methods. For more detail, please ask for our Publication No. 9118 on fire resistance.
Q: Under what conditions will Skydrol burn? A: Skydrol fluids must be heated to high temperatures before they will sustain combustion. The fire point of Skydrol LD-4, for example, is 360oF. This is the temperature the fluid must be heated to in order for it to be ignited in the ASTM D92 cup apparatus. The autoignition temperature of LD-4 is 880oF. This is the temperature at which the vapors will ignite spontaneously.
Q: Are Skydrol hydraulic fluids fire-proof? A: No. There are conditions under which Skydrol will burn. Skydrol fluids are "fire resistant." Traditionally the term "fire resistant" has been used to describe phosphate esters, as opposed to mineral oil based hydraulic fluids, because they are very difficult to ignite at room temperature. In standardized testing, a fine mist spray of Skydrol cannot be ignited with a burning propane torch. The same fine mist spray of a mineral oil hydraulic fluid, such as MIL-H-5606 or MIL-PRF-83282, produces a large fireball when touched by a propane torch.
The basic parameters of fire resistance include: 1) resistance to ignition, and 2) resistance to propagation of the flame from the source of ignition. The test methods followed by the industry are described in AMS 3150 and various ASTM test methods. For more detail, please ask for our Publication No. 9118 on fire resistance.
Q: Under what conditions will Skydrol burn? A: Skydrol fluids must be heated to high temperatures before they will sustain combustion. The fire point of Skydrol LD-4, for example, is 360oF. This is the temperature the fluid must be heated to in order for it to be ignited in the ASTM D92 cup apparatus. The autoignition temperature of LD-4 is 880oF. This is the temperature at which the vapors will ignite spontaneously.
Joined: Apr 2003
Posts: 578
Likes: 2
From: Sutton
Did some empirical tests on this a couple of decades ago (rather than believe the manufacturers story)...OK I was bored.
DTD 585 (MIL 5606 E) the mineral oil lit in the bunsen burner and we could not put it out...once withdrawn from the heat source.
The Phosphate Ester (Skydrol) fluid is "Fire Resistant" and it depends upon how you do the test....the test methods above are tightly controlled. In liquid form could not get ignition even in the bunsen burner...in fine spray form went like a flame thrower (but again as soon as the ignition source was removed it went out).
Bottom line if you have a TOTAL break of a brake pressure line onto hot brakes mineral oil is likely to ignite and PE won't.
If you have a pin prick failure of a brake high pressure line (as tends to occur on the weakend radius of a pipe bend if hit with a stone chip) then the fine spray is just waiting for an ignition source.
The main advantage of PE fluids is weight saving....over a hundreds pounds on a 747. Over the life of the aircraft very significant.
DTD 585 (MIL 5606 E) the mineral oil lit in the bunsen burner and we could not put it out...once withdrawn from the heat source.
The Phosphate Ester (Skydrol) fluid is "Fire Resistant" and it depends upon how you do the test....the test methods above are tightly controlled. In liquid form could not get ignition even in the bunsen burner...in fine spray form went like a flame thrower (but again as soon as the ignition source was removed it went out).
Bottom line if you have a TOTAL break of a brake pressure line onto hot brakes mineral oil is likely to ignite and PE won't.
If you have a pin prick failure of a brake high pressure line (as tends to occur on the weakend radius of a pipe bend if hit with a stone chip) then the fine spray is just waiting for an ignition source.
The main advantage of PE fluids is weight saving....over a hundreds pounds on a 747. Over the life of the aircraft very significant.
