Flammable Liquids Don’t Exist

By John Gilstrap

Remember that scene toward the end of “The Bourne Identity” (a really good film) when Jason Bourne shoots the fuel tank in the backyard and it explodes? Yeah, no. Wouldn’t happen. Ditto the car that blows up after getting in a wreck or after the fuel tank is shot.

Somewhere, I know I’ve watch a scene in a movie where Character A douses Character B with gasoline and lights a Zippo, threatening B-boy with immolation if he doesn’t give up the wanted information. That won’t work either because they’d both be consumed by the same fireball.

Under tightly-controlled-don’t-try-this-at-home conditions, you can extinguish a match in a can of gasoline. This is because . . .

No liquids burn. And with the exception of some metallic substances, no solids burn either. Only gases and vapors burn.

Definitions Break:

Vapors are created as liquids evaporate (create vapor). They are the same chemical composition as the liquids from which they are derived, and if they are cooled, they will condense back into liquid form.

A gas is in a gaseous state at normal atmospheric pressure and temperature. When pressurized, gases will condense into liquids, but the instant the containment is breached, the liquid will convert instantly to a gas.

Flash Point

On the coldest day of the year in most parts of the world, if you put a match into a puddle of gasoline, you’ll get a fireball because the flash point of gasoline is about -50 degrees Fahrenheit. (“Flash point” has nothing to do with a visible flash of light. When a liquid evaporates [creates vapor], the technical term for that is to flash. The “flash point” is the temperature at which a liquid begins to create combustible vapors. Given the topic, it’s an unfortunate source of confusion.)

By comparison, the flashpoint of diesel fuel is between 125 and 180 degrees Fahrenheit. On that coldest day, you’d have a hard time getting diesel to ignite because there’d be no vapors to burn.

Back when my Big Boy Job had me teaching hazardous materials response classes to corporations, one of my best clients was a company that did hardhat diving into million-gallon tanks of flammable liquids like toluene to use cutting torches to fix plumbing deep inside the tank without emptying it. There was no chance of ignition because there are no vapors in the middle of a liquid. Along the surface of the tank, it gets a little dicey, though.

But The Sign Says “Flammable Liquid”

There’s not a lot of room for nuance or subtlety on a hazmat placard. The US Department of Transportation decided decades ago that first responders should know the difference between a milk truck and a gasoline truck. They came up with their Emergency Response Guidebook (ERG). By their definition, a “flammable liquid” is one that has a flashpoint below 100 degrees Fahrenheit. A “combustible liquid” is one with a flash point between 100 and 200 degrees Fahrenheit. Labels notwithstanding, liquids still don’t burn.

Vapors Displace Oxygen, and Nothing Burns Without Oxygen

When you fill the gas tank in your car, you don’t really fill it. You leave a vapor space in the top of the tank. Those vapors displace the ambient atmosphere inside the, bringing the oxygen levels down to nearly nothing.

In your story, when you shoot a car in its gas tank, the bullet tears through a lot of liquid and a lot of vapor, but since there’s no oxygen, there’ll be no explosion. More likely, the gasoline will leak out of the bullet hole. Once exposed to the atmosphere, the spilled gas will begin to evaporate and then the vapors can burn. As more liquid spills, the fire will get bigger, but it’s hard to conceive of the circumstance where you’d get a “bang” from the gasoline. A “whump” is more feasible.

Most Flammable Vapors Are Heavier Than Air

A lot heavier, in fact. When we create that puddle of gasoline, the vapors won’t rise. If we’re at elevation, they will flow down to the lowest point. If we’re on a flat surface, they will spread out, making the hazard area of the spill much, much larger.

Uncontained Liquids Will Evaporate

Let’s go back to the guy we doused in gasoline. All that liquid we poured on him is creating an invisible vapor cloud. If we’re close enough to talk, we’re enveloped in the same vapor cloud. When you thumb that Zippo, you’re likely to have as bad a day as your intended victim.

Does It Matter?

Here’s the question I struggle with when I address the real aspects of guns and hazmats: Does it matter? Should a film director care that the really cool scene couldn’t happen in real life, or should he just go with the really cool scene? After all, we write fiction.

What say you? Does it matter?

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About John Gilstrap

John Gilstrap is the New York Times bestselling author of Lethal Game, Blue Fire, Stealth Attack, Crimson Phoenix, Hellfire, Total Mayhem, Scorpion Strike, Final Target, Friendly Fire, Nick of Time, Against All Enemies, End Game, Soft Targets, High Treason, Damage Control, Threat Warning, Hostage Zero, No Mercy, Nathan’s Run, At All Costs, Even Steven, Scott Free and Six Minutes to Freedom. Four of his books have been purchased or optioned for the Big Screen. In addition, John has written four screenplays for Hollywood, adapting the works of Nelson DeMille, Norman McLean and Thomas Harris. A frequent speaker at literary events, John also teaches seminars on suspense writing techniques at a wide variety of venues, from local libraries to The Smithsonian Institution. Outside of his writing life, John is a renowned safety expert with extensive knowledge of explosives, weapons systems, hazardous materials, and fire behavior. John lives in the Eastern Panhandle of West Virginia.

25 thoughts on “Flammable Liquids Don’t Exist

  1. Interesting and helpful post – thanks.
    When I read that Jonathan Grave does something, I know it’s going to be true and possible because of your background. I have always believed that authors do their research, so unless specifically told otherwise, I trust that what is written outside of the fictive dream is true. I have read books that prove otherwise, however, and it’s a disappointment.

    My husband was called to an accident in which a car hit a semi and went over the edge of a high railroad bridge far out in the country. By the time emergency responders got there, the car was engulfed in flames and the driver burned to death under his vehicle. Because of this, I would have believed the gas exploded. Maybe it doesn’t matter that fumes, not liquid gas, was burning, because the end result was the same. But to answer your question, I personally think it’s important to be accurate in our writing.

    • Drat! You reminded me of a point I wanted to include in the original post. There’s not such thing as gasoline fumes.

      Fumes are recondensed solids. When you weld, for example, you heat metal to its vapor temperature, and then it recondenses into what we call smoke. The smoke is comprised of tiny bits of metal and they are called fumes.

  2. Thank you for sharing your knowledge with us.

    I never believed in flammable liquids, but I thought that when a bullet hits the tank, it makes the pressure rise so quickly that results in explosion. Without oxygen, thought, it doesn’t happen, as I’ve just learned from your article. Thank you!

    Regarding to your question, this is not something that makes me turn away from a story, but in my own writings I like to follow the rules of Nature even if I have to work harder.

    • It matters to me.

      The knowledge of combustion, phase change/flash points, and “whump” allows an informed writer (which now includes me) to create story events/scenes that are authentic.
      Likewise your knowledge of guns, hazardous materials, EMS, and more is a foundation for “authentic fiction”.
      As a trauma center ER doc I (and anyone with medical knowledge/experience) know that the book, TV or movie character who is “knocked out” for extended minutes or hours would more likely end up in surgery or an intensive care unit than “coming to” and immediately carrying on their mission unimpaired. Though it is absurd, we see this instantaneous recovery in hundreds of shows.

      “Authentic – genuine, being fully trustworthy as according with fact, not counterfeit”

      Non-authentic story elements require suspension of reason. It doesn’t eliminate the potential for entertainment but the story suffers.
      The creative, imaginative manipulation of authentic facts/reality is an element of great fiction imo (e.g. recovered dinosaur DNA and Michael Crichton’s “Jurassic Park”)
      Authenticity matters to me as a reader and an author.
      Thought-provoking post and thanks for the flammable facts, John.

  3. Fascinating, John. Thanks. I may incorporate some of these facts into my new book.

    Authenticity is important to me as a writer. As a reader, I’ll suspend disbelief to a point before tossing the book. In movies, I’m really sick of the over-the-top silliness of extreme special effects. I change the channel.

  4. Thanks, John. I knew most of this but badly needed the reminder. To answer your question, it does matter. We have a generation, maybe two (or maybe three at this point) who believe that everything they see on video is true and/or real. Yes, it looks great, but it has been my experience that a lot of what looks hot and attractive is not what it seems to be and can be dangerous. That’s true across a very broad spectrum.

    Hope you’re having a great week and enjoying your new house!

  5. It’s a great question, John. I think an author needs to have a scale in the brain that favors entertainment value, but has a tipping point when things get too far removed from reality. IOW, I’ll take a little less reality if the effect is pleasing. We don’t write reality, after all. We write stylized reality for an effect.

    A scuba tank won’t explode if you shoot it with a bullet. But was there a better way to end Jaws?

    And the famous showdown between Alan Ladd and Jack Palance in Shane would not reach mythic proportions without the booming sound and Palance’s body thrust backward over a bench and into some barrels.

    So what about the fragment of folks in any of these scenarios who are experts and think, “That could never happen”? If the whole of the story is gripping, I don’t think you’ll lose many of them as potential future readers. Some, sure, but that will be offset by the many new readers you make by, gasp, entertaining them.

    • Jaws is a perfect example of throwing physics and chemistry to the side in favor of giving the audience a big cheering moment. That was a choice well made.

      I clearly need to watch Shane again. I don’t remember it as the great film that everybody else seems to think it is.

      • You have to see Shane on the biggest screen possible. In a movie theater is best. I got to see it that way for the very first time when my dad took me as a kid. I still remember the peppermint stick moment from that, and what was I, eight? several years ago I saw it onscreen again, and it was magnificent. The cinematography is stunning as befits the story.

        Big flatscreens are the next best way, and I imagine Casa de Gilstrap is set up nicely in that regard. Go for it!

  6. If a book is sold as ‘real’ rather than ‘fantasy’ in its broadest definition, it does matter to me. I’m willing to suspend disbelief to an extent. Maybe there is no Starbucks in that town, or no town at all in that neck of the woods, but I’ll let the author put them there for the story.
    If it’s science based, however, I tend to be pulled out of the story if I know it’s impossible. I’ll accept ‘highly unlikely, but it could happen under ideal circumstances–if the story is good. But don’t have a current day character smell cordite. Or get thrown across the room after being shot.
    I was reading a book where the prologue has a car going over a cliff, hitting an outcropping and exploding in a huge fireball. The firefighter said the car must have had a full tank of gas. I was willing to cut the author some slack, as I figured there’s the whole rest of the book and maybe an investigation would show there was actually some other explosive in the car that caused it to explode. I’m not finished reading yet, so I don’t know whether that thread will be dropped, but so far the rest of the book hasn’t touched on the actual forensics.

    • Interesting you mention cordite, Terry. We at KZB have been taught, by John and maybe others, about cordite being ancient history. But the rest of the world hasn’t learned.

      I just read a story in Best American Mystery Stories 2020 in which the MC smells cordite. The story setting is more or less contemporay, as there are references to the Medallín cartel.

  7. This is a fascinating post. A lot depends on how fiction is marketed. When you read Tom Clancy or Mark Greaney, you demand guns and gadgets and tech be totally accurate (if not necessarily deployed realistically).

    With most fiction, though, I feel like the decades of inaccurate flammability have probably created a fake news scenario where we expect gasoline to ignite and cars to blow up.

    • It’s the same with decades of cops arresting a guy and immediately reading him his rights. In real life, they don’t do that until much later, because anything the guy says on the way to the station, etc., is admissible. But after so many episodes of Law & Order, a reader will think if your cops DON’T Mirandize as they put on the cuffs, you’ve blown it!

      • Jim, it’s been my experience that the guy being dragged to the squad car kicking and screaming “I know my rights!” invariably does not.

        There’s sort of a parallel universe at work here once he gets booked and starts caucusing with the legal savants in the dayroom. Then you spend valuable time talking him down off whatever ledge they’ve gotten him to walk out on.

        When I worked on the floor at McDonnell Douglas in Long Beach they called it “tribal knowledge”-things that people know because they just know and that’s the way they’ve always done it.

        All this points to what John is talking about.

        We’ve revisited this theme of about regionalisms and terroir. Authenticity is critical to being true to the story.

        Of course the fantasy boys and girls can make up anything they want-exploding crystals from space with mysterious powers, characters with names that always end in -th with super powers, but as someone here remarked about superheroes it can be a species of deus ex machina or in our case a crutch to inaccurate writing.

        Maybe the reader wouldn’t know but I’d know.

        • I was at Douglas’s A-Plant in Santa Monica for 3 years, working on the Saturn S-IVB. One day, an elderly woman arrived to sew up some hose insulation for us. She was the seamstress who had sewed the cushions for the DC-1. And where would Star Trek be without “dilithium crystals?”


  8. Very informative post, John. Thank you. While I knew some of this, your explanations really rounded things out for me. The question of realism vs. entertainment is an important one. I think Jim’s point about writers needing a scale in the brain to weigh that issue is good approach. The other factor, as he and other commenters pointed out, is the way in which Hollywood has trained viewers (and thus, readers) to expect certain physical outcomes, such as a fireball when a car smashes into the ground after plunging down a hillside, or someone doused in gasoline will erupt in the flames.

    I think at the very least it’s good to be judicious with the unrealism for dramatic effect, and not go too over the top, and to not be “unrealistic” too often in the course of your novel. At the same time, knocking some one out and having them wake up later, groggy but otherwise unharmed, for instance, is a useful narrative device 🙂

    Have a great day!

    • The exploding vehicle has, worse yet, become a cliché best avoided like the plague, unless you’re trying to be funny.

  9. Thanks, John, for this post and the useful information. It will be helpful when I return to writing thrillers. In the meantime, as I continue a fantasy series, I’m enjoying inventing my own chemistry and laws of physics.

    Have a safe week.

  10. I’ve always believed that novelists should be held to a higher standard of accuracy than any other type of media entertainment. Our readers are certainly smarter, and they don’t go brain dead when action happens. “Oooooh, shiny and explodey,” isn’t their natural reaction because they have to do the work of creating the images in their heads.

  11. Great post, Sir John. I look for authenticity in books I read, but I must confess, not so much in movies.

    If the characters in a movie have depth and the dialogue is good, and I really need to know what happens at the end, I’ll put up with a wee bit of exploding gas tanks (my husband always points out to me when “that wouldn’t happen if it wasn’t Hollywood”. . . ). But if the action gets too silly, I’ll stop watching.

    Thanks for the great info. Maybe the next time we watch a movie together, I’ll be able to turn the tables on Alan. 🙂

  12. I appreciate the information, John. I learned a lot from your post.

    I agree with Jim. “I’ll take a little less reality if the effect is pleasing. We don’t write reality, after all. We write stylized reality for an effect.”

  13. A long time ago, a friend worked in a service station where the owner kept a coffee can with a half inch or so of gasoline in it, on the ground, out of the way. Several times a day, the owner would toss his (lit) cigarette into the can on the way to the pumps. The can ignited only once in two years. The owner simply put a metal lid on the can to put out the fire. Don’t try this at home.

    Then there was the famous “Dateline” fake news, where NBC belatedly admitted it used incendiary devices to ensure that a fire would erupt if gasoline leaked from a brand of pickup truck being hit by a test car. “[T]hey used remotely controlled incendiary devices to spark a fire . . .” (Those trucks apparently did have a higher-than-average tendency to ignite if the side-mounted fuel tank was punctured in a collision. Gasoline vapors released in a collision can be ignited by the ignition system of either vehicle or any open flame nearby.) 0

  14. It’s one thing if the action, explosion, whatever, requires specialized knowledge to know how something should react. When it’s basic knowledge learned in grade school, it’s another. I saw a thriller series TV show a few months ago where we see our heroes in a city on the East Coast of the US, and from the vegetation and how people are dressed, we’re into summer. Then we jump to an Antarctic base where some nasty bats have shorted out the one tiny space heater that heats the entire base, and where the bats are covering the solar panels, preventing any alternate energy source to be used for heat. Is there a fifth grader alive who doesn’t know that when it’s summer in the Northern Hemisphere, it’s winter in Antarctica? And when it’s winter, the sun doesn’t get above the horizon. How would solar panels work even if they weren’t covered in bats who’ve unbelievably flown through a blizzard and over a thousand miles of open ocean to get there and haven’t frozen to death? Where was the science advisor? I gave up on the show during that episode.

    I had the pleasure of sitting beside an ex-Navy submariner during a James Bond film. During the tense final fight, the sub tips at a very steep angle. My friend laughed and said, “If the angle was that steep, in that harbor, a third of the sub would be sticking out of the water. The harbor just isn’t that deep.” Then we both laughed when the good guys pulled the rods out of the run-away nuclear reactor to slow it down. Yikes! They got it backwards!

    I’m happy to suspend disbelief for the sake of the story, but mucking up the most basic science is a bridge too far.

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