How Hot Does Cooking Oil Need to Be Before It Catches Fire?

Posted by Eric Troy on 05 May 2014 15:43

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Here are some facts about grease fires in the kitchen which will bring home to you just how dangerous being careless with cooking oils can be. I am going to provide you with a lot of in-depth information about cooking fires.

The answer to the question posed in the title cannot be answered in a few short sentances and still prepare you adequately for cooking oil fires. If you want to know how hot cooking oil needs to be before it 'catches fire' all by itself, it depends on the particular oil, but expect the autoignition point to be between 400 to 435°C (750 to 815°F), If you would like, you can skip to whether cooking oil is flammable, or see the information on the flash point or ignition temperature of cooking oils.

See also: Can You Deep Fry With Olive Oil?

But, because safety in the kitchen is the first consideration, let's quickly go over the best way to deal with a pan fire like the one in the photo below. For some reason, on cooking shows, some cavalier chef always picks up the pan with an out of control fire in it and carries it to a sink. This is stupid. They could spill grease from the pan and thus spread the fire, including to themselves and others. Throwing the pan into the sink could splash oil around and cause even more injury. But let's start with some statistics and other information.

What is the Main Source of Home Cooking Fires?

First, let's understand where the biggest risks lie. Most home cooking fires involve ranges or cooktops; well over half. And most deaths or serious injuries from home cooking fires are started on stove tops. The second largest source of home cooking fires are ovens, but almost no deaths or injuries result from these, as compared to stove top cooking fires. The same thing goes for hotplates and similar appliances, microwave ovens, grills, hibachis, deep fryers, etc. Much fewer serious injuries or deaths occur from cooking fires related to these appliances. The reasons for that may not be, necessarily, that these appliances are less dangerous. Deep fryers, for example, may not be common enough in the home to be compared meaningfully with stovetops, on a statistical basis. And although outdoor grilling is extremely common, and serious accidents do occur, people may tend to have a bit more respect, and treat grilling with a more caution, than stove top cooking.

You may have also heard many times about the danger of dirty grease hoods or exhaust fans, but again, very few fires (1%) actually result from these, as compared to ranges or cook top stoves. This is not to say that all these other types of equipment cannot be dangerous, of course. In general, the leading cause of home fires and fire-related injuries has long been cooking equipment. However, you should realize that cooking equipment being named as a cause of home fires is not meant to indicate that the equipment malfunctioned. It simply means that the cooking equipment was the source of heat for the fire. It is actual human error that is more often the cause, rather than equipment malfunction. Many of the modern safety features found on heat-producing appliances, such as automatic shut-off mechanisms, are designed to compensate for human error.

Home grease fire on electric stove

Home grease fires are more likely on electric stoves. Weird, but true!
Image by State Farm via Flickr

Home grease fire on electric stove

Home grease fires are more likely on electric stoves. Weird, but true!
Image by State Farm via Flickr

There are many scenarios that lead to cooking fires: Food being left on the burner unattended; a combustible material being left close to the heat source (gas flame or electric burner); stove accidentally being left on, etc. However, the majority of cooking fires are actual food ignitions on the cook top, with most of these being the ignition of cooking oil. As well, many of these fires occur from the oil being overheated before any food was ever added to it. Therefore, it is important to understand the dangers of cooking oils, when it comes to kitchen fires. Ignition of hot cooking oil is the source of 75% of home kitchen fires.

Which is More Dangerous, Electric or Gas Stoves?

This is going to surprise you. Electric stoves seem to be more dangerous than gas stoves with flame burners. You would think that an open flame is more likely to be an ignition source for hot oil. However, more fires occur from electric stoves. There are some reasons for this, and once we go over them, you'll see immediately that it makes sense.

1. It is more obvious that gas stoves are on. People forget to turn off electric stoves more often because sometimes the glow from the electric coil is not that apparent. It is harder to miss a flame. Plus, there is at least a bit of sound coming from a gas flame. A slight hiss.

2. When you turn off a gas stove, the heat source is pretty much gone. When you turn off an electric stove, the heat from the electric coil does not immediately go away. It takes a while for it to cool down. This is the very reason chefs like gas stoves better: There is more control over the heat source. We'll get to why this ability to quickly remove the heat source from a fire is important a bit later.

3. With a gas flame burner, you can adjust the flame so that the heat source (the circle of flames) stays underneath the pan, and does not necessarily come out around the bottom edges. If an electric burner is too big for a pan, there is nothing you can do about it, meaning that there is an open heat source. Of course, we often set a gas flame on high to begin heating oil, so that is why this is the third, and least significant, reason.

using a lid to extinguish a grease fire in pan

A grease fire like the one in this photo can usually be extinguished
simply by placing a lid on the pan, as depicted. This will cut the fire
off from oxygen and so smother the flames. To use a lid, hold it
by the handle at a slight angle to the flames, so that the lid
acts as a shield. Then carefully slide the lid over the pan, from front
to back. Don't panic and try to throw the lid on, as this might splash
the hot oil and spread the fire.

using a lid to extinguish a grease fire in pan

A grease fire like the one in this photo can usually be extinguished
simply by placing a lid on the pan, as depicted. This will cut the fire
off from oxygen and so smother the flames. To use a lid, hold it
by the handle at a slight angle to the flames, so that the lid
acts as a shield. Then carefully slide the lid over the pan, from front
to back. Don't panic and try to throw the lid on, as this might splash
the hot oil and spread the fire.

Safety Rules for Hot Oil Fires

Rule 1: If a pan of hot oil catches on fire, turn off the stove! For some reason, articles on food safety always skip over this part. You might just find that if you simply remove the source of flame, the fire will go out all on its own. This will depend on whether you are cooking with a gas or electric stove, but it's always a good idea to turn off the heat, as long as you can do so safely.

Rule 2: Always have a lid handy. If a fire ignites in a pan like the one in the image above, slip the lid onto the pan from the front to the back. That should extinguish the fire very quickly. The key is not to panic and to act quickly. You may also have read about pouring salt on it, or baking soda. This works, but is inefficient and dangerous. While dumping on the salt or baking soda, depending on the amount of oil in the pan, you can displace the oil and thus spread the fire, including to yourself. If you do use baking soda or salt throw it onto the fire from a few feet back rather than trying to pour it onto the fire. Only use a lid or baking soda to extinguish the flame when the fire is small and contained in the pan. Once it has spread beyond the pan, it is best to use a fire extinguisher or fire blanket (more below).

Rule 3: NEVER pour water on a grease fire! Water will not put out a grease fire, it will only spread the fire and make it worse, perhaps MUCH worse. You know what happens if you drip even a small amount of water into hot cooking oil. The oil pops and splatters. Pouring water onto oil that has caught fire can cause the oil to almost erupt, exploding out of the pan and scattering in all directions, taking the fire with it. A water mist, if very fine, can be used to extinguish grease fires, because the mist does not cause such large splattering, but unless you have a water mist extinguisher, which is doubtful, do not try this.

Rule 4: Always have a good fire extinguisher or fire blanket. Most home fire extinguishers come with a wall mounting bracket so that you can store it within easy reach near where you cook. For home grease fires, the newest and most effective type of extinguisher is a wet chemical class-K like the Amerex Wet Chemical Class K Extinguisher. This type uses a potassium acetate based extinguishing agent with a low pH which also cools the fire as it extinguishes it. This can be important to prevent re-ignition (more on this later).

Most people will want an all-purpose fire extinguisher, which is usually a dry chemical extinguisher such as the Amerex 5lb Dry Chemical Class ABC Fire Extinguisher. This is rated for class A, B, and C fires. Oil fires are class B fires. These are fires that involve flammable or combustible liquids, which include oil, gasoline, and other similar materials. Anything that cuts off the fire from oxygen, smothering it, works well on this type of fire. The "Class K" from above may be confusing, since it would seem to indicate two different types of fires, but K simply stands for kitchen, and indicates fires that are more typical of kitchens, such as vegetable oils or animal fats, whereas class B fires cover all sorts of combustible and flammable liquids, not all of which need to be hot before igniting (more on flammable versus combustible below).

When using a fire extinguisher on a grease fire aim at the base of the fire while standing around 10 feet away. For more information on the use of a fire extinguisher see Know How To Use Your Home Fire Extinguisher!

To use an emergency fire blanket, simply lay it over the fire to smother the flames. Fire blankets can work well on smaller fires that are mostly contained, but still a bit larger than a fire you could put out by simply putting a lid on the pan. Fire blankets are also very good for smothering flames on a person's clothing.

How do Grease Fires Start?

Now, to the part you probably didn't know. There is more than one way for a kitchen grease fire to erupt. First, let's say you are heating oil in a pan on the stove. It has to get to a certain high temperature before it can ignite, or, in other words, catch on fire. Why?

Well, this is because liquid oil itself does not burn. Rather, it is the vapor from oil that has reached its boiling and vapor point that ignites. There are three things, for our purposes, to understand. The flash point, the fire point, and the ignition point.

Flash Point of Cooking Oils

The flash point of a flammable liquid material is the lowest temperature at which the material, our vegetable oil, can form an ignitable mixture in air. This means that it is giving off vapors that can be ignited by an ignition source. Usually, at home, this ignition source is the source of heat that is heating the oil, your gas burner or electric stove. As already mentioned, an electric burner is more likely to ignite a hot cooking oil than a gas flame.

The ignition source has to be somewhat hotter than the oil. Now, comes the fire point. The fire point is the temperature that must be reached for the vapor to continue to burn after being ignited, even if the ignition source is removed. This explains why, as I mentioned above, sometimes just turning off the flame will stop the fire. At a certain temperature, the oil will need a continued source of heat to continue burning. When you turn off an electric stove, of course, the burner remains hot for a while, so you are not really immediately removing the heat source. On a gas stove, once the flame is off, it is possible for an oil that has reached the flame point, but not fire point, to go out. But don't depend on it! For the fire to be self-sustaining, the temperature has to be a little hotter than the initial flash point.

Is Vegetable Oil Flammable?

You may have been wondering whether olive oil is flammable, or any other oil. Technically, vegetable oils and oils in general are not flammable. The fact that vegetable and animal cooking oils have very high flash points (above) is part of why they are not considered hazardous materials. Consider a household chemical which will ignite at room temperature and compare this with cooking oil, which must be heated to a very high temperature before a flame or spark can set it off. The flashpoint, in fact, is used as a dividing line between when a liquid is considered flammable or combustible.

Cooking oils are not flammable, but once they reach their flash point and are ignited they can burn very intensely. A fire from a hot pan of grease can seem like a raging inferno. So, although they are combustible liquids rather than flammable ones, and they are not considered hazardous materials, you should consider them potentially very dangerous, indeed. The cut-off point between a flammable and combustible liquid is usually considered a flash point of 100°F (38°C), with anything under this being a flammable. Vegetable oil and cooking oil in general will not just light on fire, but once it reaches a high enough temperature to ignite, it will burn fiercly, being hard to extinguish.

The flash point of a vegetable oil could be affected by how it is refined, and whether solvents were used. If solvent residues are left in the oil, which could be dangerous, the flash point will be lower. It would not be possible to give an accurate flash point for all types of oil, such as corn, canola, olive, peanut, sunflower, etc., but they are somewhere between 300 to 330°C (572 to 626°F). The average flash point for cooking oils is usually given as 600°F.

Ignition (or Auto-Ignition) Point of Cooking Oils

Although some home grease fires happen when oil hits its flash point, and then somehow comes into contact with the ignition source, this is not the only way for an oil to catch fire. There is, instead of the flash point, the ignition temperature or what is sometimes called the autoignition temperature. This is the minimum temperature required to initiate a self-sustained combustion in the absence of a spark or flame.

This means that heat is transferred to the oil by some external source, such as the stove burner, and the oil is heated until it reaches the temperature at which spontaneous ignition can occur, without actually coming into contact with a flame or a spark.

Of course, you may have heard of the spontaneous combustion of piles of hay or compost heaps. This is unusual but it involves heat produced from biological processes by bacteria and a very slow oxidation within the material. The heat, which slowly builds up from the bacteria metabolizing, must be confined within the heap of hay, straw, or compost, and unable to escape, so that it causes the material inside to reach its autoignition temperature, at which point it spontaneously bursts into flames. When this happened in olden days, it must have really freaked people out. They probably thought the hand of God had reached down and started their hay on fire.

But with oil, of course, we are talking about heating it through some external source of heat, until it reaches a temperature sufficient for it to auto-ignite. Here is the weird part: Once a Vegetable oil has reached its flash point, and has ignited, it is possible for the autoignition temperature to become lower. This means that re-ignition may occur after the flames have been extinguished, unless the oil is cooled down to below the new autoignition temperature. If you have ever seen or experienced the phenomenon of a grease fire being put out, and then spontaneously bursting back into flames a moment later, this is the reason. That is why I mentioned the new Class K Wet Chemical Extinguishers for grease fires, since they not only extinguish the flames but also cool the oil.

It would be difficult to give accurate autoignition points for all cooking oils, but expect between 400 to 435°C (750 to 815°F), and you'll be in the ballpark. That is raging hot, and you've really got to be out to lunch to let this happen, which is why such accidents tend to occur when heating oil is left unattended and forgotten. In fact, this is the number one way such fires occur.

Smoke Point of Cooking Oils

Of course, you do not need to know the precise temperature to avoid a grease fire. You simply need to constantly attend to your cooking and know the warning signs. One confusing term you will come across, when researching grease fires, is the smoke point of an oil. Most authors on the internet seem to assume that the smoke point of an oil is the same as the ignition point, that is, that when an oil smokes, it is just about to burst into flames. This is not the case. The smoke point of an oil has to do with how refined it is, with more refined oils having higher smoke points. The smoke point may well occur up to 200 degrees lower than the ignition point. However, once an oil has reached its smoke point, it is definitely time to turn down the heat, as the oil is becoming too hot! As the oil continues heating (and the temp will rapidly increase) the smoke will, of course, become worse and worse.

The three common cooking oils with the highest smoke points are peanut oil, safflower oil, and soybean oil, which all have smoke points of approximately 450°F. Be aware that approximate really does mean approximate, as any one oil may start to smoke at a little higher or lower temperature. These are averages. The smoke points for common cooking oils are given below, from highest to lowest:

  • Peanut Oil: 450°F
  • Safflower Oil: 450°F
  • Soybean Oil: 450°F
  • Grapeseed Oil: 445°F
  • Canola Oil: 435°F
  • Corn Oil 410°F
  • Olive Oil: 410°F (See Can You Deep Fry With Olive Oil?)
  • Sesame Seed Oil: 410°F
  • Sunflower Oil: 390°F

Boiling Point is the Final Warning Sign

Although smoking oil should be enough of a warning to you, when an oil reaches its boiling point, it is getting very close to auto-igniting. And, once it is boiling, the temperature of the oil will increase very quickly. Hot cooking oil should never be allowed to reach a boil without any food being added. If this occurs, turn off the heat completely and allow the oil to cool down to below boiling. Having a thermometer handy to test when the oil is at its proper cooking temperature would be good, in this case.

911 is Not a Last Resort

Hopefully, with the information given here, you are more conscious of fire safety when cooking and will be able to prevent a fire from occurring. However, should a fire occur in your home or if any other emergency occurs you should never hesitate to dial 911 and activate emergency services. Many people consider this to be a last resort. It is NOT. Knowing the information given here, and even being prepared for a fire and other emergency situations, is no guarantee. No matter whether you know some basic steps for putting out a small fire there is absolutely no guarantee that you will be able to successfully put out a fire in your home. Never take this type of information, or your own preparation, as a substitute for professional help. Your fire department exists to protect you from harm.

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