Is aviation hydraulic fluid flammable?

This blog post will answer the question, “Is aviation hydraulic fluid flammable” and cover topics like the flammability of hydraulic fluid, and frequently asked questions related to the topic.

Is aviation hydraulic fluid flammable?

Most aviation hydraulic fluids are flammable. Although petroleum-based hydraulic fluids have a relatively high flash point, they atomize in air when released at high pressure. This means that they ignite easily when they come in contact with a heat source.

What Is Hydraulic Fluid and How Does It Work?

Hydraulic fluids are divided into two categories:

Hydraulic Fluid Made from Crude Oil: A thin oil-based fluid with a water viscosity.

Synthetic Hydraulic Fluid: A viscous liquid manufactured from petroleum products that do not need the addition of thinner base oil in certain applications.

Is Hydraulic Fluid Flammable Or Combustible?

At the same time, yes and no! Because of their source ingredient and flashpoint, hydraulic fluids are particularly combustible. However, depending on the variety, they may or may not be combustible. Hydraulic fluids are divided into two categories: petroleum-based and water-based.

The flammability of hydraulic fluids varies based on the variants:

Petroleum-based hydraulic fluidsWater-based hydraulic fluids
Petroleum-based hydraulic fluids are more flammable than water-based lubricants.Because of their nature, water-based hydraulic fluids are practically non-flammable.
Mineral oils are abundant in petroleum-based hydraulic fluid. As a consequence, the material becomes more flammable.The ones that are water-based have greater water content. The greater the water content, the less flammable it is.
They have a flashpoint that may be reached, causing them to ignite.These fluids’ flashpoints are difficult to attain, resulting in incombustibility.

What Causes Hydraulic Liquid to Become Flammable?

Hydraulic fuel isn’t very combustible. However, it is very flammable and may catch fire on a regular basis. Because of their greater ignition point, they are not a fire danger. However, they continue to produce flammability for a variety of causes, some of which are listed below:

  • Hydraulic fluid is made up of 99 percent of the entire volume of the base ingredient. Mineral oil is that element, and it interacts quite effectively with fire. As a consequence, they’re combustible.
  • Any substance’s flammability is also determined by its flashpoint. The lower the flashpoint, the simpler it is to burn important materials in a fire. Hydraulic fluids may catch fire and cause flames due to their intermediate flashpoint.
  • The hydraulic fluid may reach the ignition temperature more easily, perhaps sparking a fire.

What Are Hydraulic Fluid’s Dangers?

Every action has an equal and opposite response. Hydraulic fluids provide several benefits. Some of the disadvantages are also to be expected. These flaws pose a number of risks to the environment and our daily lives, some of which are listed below:

  • Hydraulic fluids have a significant negative impact on climate and the environment. They pollute the air, water, and soil, resulting in environmental contamination. These factors have the potential to alter the global climate and cause global warming.
  • They are combustible and emit hazardous poisonous smoke as a result. When breathed, these gases are very toxic to the human body and cause lungs damage. As a consequence, a variety of cardiac ailments develop.
  • They may cause bronchitis, asthma, and a variety of other illnesses, as well as fluid injection injuries, sliding, falling, and tripping dangers, among other things.

What Are The Advantages Of Hydraulic Fluid?

  • It has a low coefficient of friction, making it perfect for usage in situations where there is a lot of movement or high weights.
  • Because of its low viscosity, it may minimize noise when compared to other oils (thickness).
  • It is more ecologically friendly than other oils since it does not include any hazardous compounds, as do most other oils.
  • It may be combined with other oils to make Hydraulic System Fluid, which can be used for a variety of motor oil and transformer oil applications (HHF).
  • Hydraulic fluid has the ability to overcome the effects of friction on moving components due to its properties. As a result, hydraulic fluid is frequently used to lubricate heavy gear like power plant generators and stationary motors.
  • It is also regarded as a high-performance product since it has a longer service life at higher temps than other oils, but it lacks the durability of its equivalents when stored for an extended period of time (Shelf Life)
  • Hydraulic fluid, with its potential to drastically decrease friction, may assist boost productivity and profitability in specific industries, such as manufacturing and transportation systems, by lowering the cost per unit value.

What Temperature Ignites Hydraulic Oil?

Every flammable material has a unique ignition point. That is to say, at certain temperatures, the burning sensations begin to burn. This is referred to as the “flashpoint.” Hydraulic oil, like other chemicals, has certain flashpoints when it starts to ignite.

The temperature of the oil’s ignition point is shown below:

Once hydraulic fluids reach a flashpoint, they become flammable. They begin to reach their flashpoint at temperatures exceeding 300° Fahrenheit. They usually burn between 300 and 600 degrees Fahrenheit Celsius. The oil’s auto-ignition point is roughly 475 degrees Fahrenheit.

What Is Hydraulic Fluid’s Flashpoint?

The minimum temperature at which a liquid will burn is the flashpoint of hydraulic fluid. 

It is critical to understand the Flashpoint of hydraulic fluid in the event of an unintentional fire, since it may be dangerous to human life. The hydraulic fluids have a flashpoint of 214 ° C. 

What Is  Fire-Resistant Hydraulic Fluid?

Water-based hydraulic fluids are used as an alternative to petroleum-based hydraulic fluids in the event of a fire. Where there is a danger of igniting, water-based hydraulic fluids are utilized, and petroleum should be avoided. These hydraulic fluids provide the hydraulic energy required to complete the operation.

Hydraulic fluids that are fire-resistant are non-flammable and have no danger of catching fire. Water hydraulic fluids, which contain much more water, are the only ones capable of doing so. The fluids are unable to ignite due to the presence of water.

What Are The Dangers Of Using Hydraulic Fluid In A Plane?

The following are some of the dangers of utilizing hydraulic fluid in an aircraft:

  • Leaks and fires may occur if the right fluid is not used or if the fluid is not changed often enough.
  • Hydraulic fluids are poisonous and must be properly disposed of, including all safety procedures.
  • Passengers and members of the crew may be exposed to harmful gases from a leaky hydraulic system.

How Can Hydraulic Oil Fires Be Prevented?

It is always preferable to prevent than cure. However, in order to avoid this, one must first identify the cause of the barriers. A fire, for example, might be the most severe impediment to hydraulic oils fulfilling their function. And it is the mineral oil, which makes up the whole fluid, that is mostly to blame for this fire.

The following are the steps that must be taken to avoid hydraulic oil fires:

  • Mineral oils are mostly to blame for hydraulic oil fires setting the fire. Non-combustible fluids should be used instead of mineral oils.
  • Water, one of the most efficient extinguishers of all time, is one of these non-combustible fluids.
  • Hydraulic oil fires may also be avoided by utilizing water-based oil as a replacement for petroleum.

Categories of Hydraulic fluids 

Hydraulic fluids are divided into many groups, as previously stated. These are the following:

  • Mineral oils are a kind of oil that is used
  • Fluids that are resistant to fire
  • emulsions of water and oil
  • Glycerin (water)
  • Esters of phosphorus

Mineral oils and other petroleum-based hydraulic fluids have a flashpoint of 300 to 600 ℉. The minimum temperature at which vapors may ignite is called the flashpoint.

Hydraulic fluids based on water are combustible. When employing these sorts of fluids, however, corrosion may be a problem. 

Oil and water emulsions, Anhydrous Synthetics, and Water-Polymer solutions are the most common types of fire-resistant hydraulic fluids.

What are the Different Types of Hydraulic Fluids Used in Aircraft?

Aircraft Hydraulic Fluids

In comparison to industrial fluids, hydraulic fluids used in airplanes are rather thin. They should also be fire resistant, which really is essential when the closest fire station is 5 miles distant rather than a few streets away. Hydraulic fluids used in aviation vary from those used in industrial applications as they must maintain a temperature range of -65° to 275° F. Aqueous and vegetable-based oil lubricants will boil or freeze at such temperatures. 

The following are the most common hydraulic fluids used in commercial and military aircraft, based on the application and environment:

MIL-H-5606: For more than fifty years, the MIL-H-5606 has been utilized on a variety of aircraft. It’s still in use on select Air Force flights and corporate jets in the United States. However, since it is very combustible and has been linked to the loss of military planes in the past, it is not utilized as often as it formerly was.

MIL-H-83282: The Air Force has been using MIL-H-83282 hydraulic fluid in aircraft since 1982, and it has been the predominant fluid in Navy planes since the late 1990s. Its appeal stems from the fact that it is much less combustible than 5606. At low temperatures, however, it becomes more viscous, with a lower limit of just -40° F.

MIL-H-87257: A newer version, MIL-H-87257, is utilized in C135, E3, and U2 airplanes. It’s also less combustible than 5606 and can withstand temperatures as low as -65° F. In recent airplanes, it has become the preferred hydraulic fluid.

Skydrol: Eastmen aviation solutions manufacture Skydrol, a phosphate ester technology that has been known in the industry as the very first fire-resistant hydraulic fluid.

Hyjet: ExxonMobil’s Hyjet hydraulic fluid is compatible with all Type IV and Type V hydraulic fluids, as well as elastomers and other hydraulic system components. 

Frequently Asked Questions(FAQs), “Is aviation hydraulic fluid flammable?”

Is the hydraulic oil used flammable?

Once hydraulic fluids reach a flashpoint, they become flammable. They begin to reach their flashpoint at temperatures exceeding 300° Fahrenheit. They usually burn between 300 and 600 degrees Fahrenheit Celsius. The oil’s auto-ignition point is roughly 475 degrees Fahrenheit.

Why is it forbidden to combine airplane hydraulic fluids?

Hydraulic fluids mixed together may cause a system to fail. Because of the variations in composition, petroleum-based and phosphate ester-based hydraulic fluids must not be mixed. Neither exchange seals nor a specific fluid is mentioned.

Is hydraulic oil flammable?

Oil auto-ignition and overheated component ignition are additional possibilities. Similar blasts may occur in big diesel engines when lubricating oil mist ignites and the interior volume of the crankcase is large enough to enable a powerful explosion to occur.

Is it true that hydraulic acid is flammable?

It is neither flammable nor combustible in any way. Use extinguishing methods that are suited for the local environment and conditions. If required, use self-contained breathing gear to battle fires. The product does not burn on its own.

What causes the red color of airplane hydraulic fluid?

Petroleum is used to make mineral-based hydraulic fluid (MIL–H-5606). It has a reddish-brown color and a strong oil-like odor. Petroleum-based fluids are sealed using synthetic rubber seals.

Is it possible to combine engine oil with hydraulic fluid?

It is never a good idea to mix oils with various additive packages. This might affect both elements’ additive effectiveness, induce component surface corrosion, and result in higher mechanical wear.


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