Do people actually drive around town with a bomb on their bumper?
October 17, 2021 4:27 PM   Subscribe

Here in urban south central Wisconsin, where there is a gas station within sight most of the time, it is not uncommon to see someone driving around with a bright red gas jerrycan strapped to their 4Runner, Wrangler, or Tacoma, often in a place that is vulnerable to being rear ended. Are these empty, or are people actually driving around with all this extra gas in a very dangerous place, “just in case?”

The cans are not alone of course. Lift kits, winches, rooftop tents, jacks, the occasional snorkel, etc are all part of the package. I don’t really care about this hobby, but I just can’t wrap my brain around the extra gas on the rear bumper, roof rack, or spare tire because it’s so dangerous and unnecessary.
posted by rockindata to Travel & Transportation (19 answers total)
 
I suspect they are mostly empty most of the time. Because yes they are a bomb, but also are very easy to siphon. But where else to put your jerry can for your vehicle than on your vehicle's jerry can holder? They're there for when they are needed.
posted by turbid dahlia at 4:32 PM on October 17, 2021 [1 favorite]


I think most of them are actually filled with water for an overheating radiator or other uses one might have for water while driving in off road or wherever. Storing gas long term like that isn't really practical.

Plus, I mean, a jerry can looks cool on the back of a Jeep.
posted by bondcliff at 4:36 PM on October 17, 2021 [7 favorites]


Presumably the Jerry cans are only full of gas when the owner is headed off-road or into the wilderness, where there aren’t any gas stations and no other cars to rear end you.

The rest of the time they’re filled with margaritas for tailgating, I imagine.
posted by ejs at 4:50 PM on October 17, 2021 [10 favorites]


Gas is much more flammable than explosive when not pressurized. Gas engines use compression to increase the ability of gas to detonate. Consider that your car's gas tank is in the back/bottom of your car even though it is potentially more vulnerable to being damaged during a collision.

I'm not going to say carrying around a filled can of gas on the back of a car unnecessarily is a great idea. As a non-safety matter, it will evaporate and get stale pretty easily. However, it is objectively not a bomb.
posted by saeculorum at 5:08 PM on October 17, 2021 [18 favorites]


Some of these would be tradespeople, as well as campers, because fuel cans are needed to run other engines at worksites (think small generators, petrol saws and cutters, pumps, and so on). Anyone using two-stroke engines does need a jerry can to prepare the oil/fuel mixture.
posted by Fiasco da Gama at 5:11 PM on October 17, 2021 [5 favorites]


Would you rather have the off-gassing smelly can of bomb inside the car? You don't want that inside, you might pass out from the fumes or light a joint and go boom and if nothing else your car's going to smell of gasoline and make you sick. It's safer on the outside, keep the boom stuff outside of everybody's inside. Plus outside of big cities and such, who's going to stop to help a stranded traveler? Out in the wilds where this is more likely to be seen it's the folks who have a can of gas on the back and road flares and jumper cables both for their use and just to be able to help.
posted by zengargoyle at 5:11 PM on October 17, 2021 [6 favorites]


I think they are just cosplayers.
posted by nothing.especially.clever at 6:26 PM on October 17, 2021 [13 favorites]


Best answer: I used to have a Jeep and know a bunch of people with modded JKs, and yeah it's a pretty popular mod to put a Rotopax (or other can, but Rotopax are at the top of the gas can dick-measuring hierarchy) on the back of the spare tire mount.

I never heard of anyone keeping water in one. Like, ever. Water is easy enough to store inside the vehicle, and storing it in a fuel can would (1) make the water unusable for human purposes, (2) pollute the can with water, which you'd have to thoroughly dry out before using it for gasoline, (3) be a waste of a fairly expensive gas can to store something you can keep safely in milk bottles, and perhaps most importantly (4) might result in some "helpful" dingus putting water into your gas tank. Also, it would get you sneering looks from the other 4WD people, because there is an actual Rotopax water can, you cheapass. (The 4WD modding scene is not really one for people without a bunch of disposable income.)

Most people with those cans either put gasoline+Stabil in them, which makes the gas good for 6 months or so, and/or "rotated" the gas through the can by pouring it into their main tank and then refilling the rest of the tank + the can when they bought gas regularly. Or they just left the cans empty when they weren't really using them (Ropaxes are lockable).

Anyway, the safety of them only came up once or twice, and the consensus opinion seemed to be: first, that by being mounted on the spare, they're above the likely impact point of most rear-end collisions, and two, by being at the rear of the vehicle, if they did rupture, the likely scenario was for the gas to spill onto the hot engine of the asshole who just rear-ended you, thereby burning them alive while potentially giving you time to escape. This was regarded as a feature rather than a bug.

I couldn't really argue with that too much, because at the time I drove a KJ, which was somewhat infamous for having a basically unprotected main fuel tank located just forward of the rear bumper and low to the ground. (Chrysler eventually admitted that this was a problem, and offered as a solution a free trailer hitch to "protect" the tank, if you didn't already have one installed.) Between the time the problem was identified and when Chrysler gave me a free hitch, I did consider getting a bumper sticker that said "Warning: Equipped with a Chrysler rear-end collision self destruct mechanism".
posted by Kadin2048 at 6:34 PM on October 17, 2021 [24 favorites]


Back when I ran my Jeep on the beach, I kept two cans filled for me or others as needed. Sometimes people didn't bring enough to run the generator. After the trip, I'd drain the cans into the car and leave them empty until needed again. We had a white plastic can (same form as a Jerry can) to carry water, but it broke and we just carry bottles now.

I have thought about getting one of these... but just to show off.
posted by Marky at 10:45 PM on October 17, 2021 [2 favorites]


They're full of sherry.
posted by flabdablet at 2:16 AM on October 18, 2021 [1 favorite]


An interesting cultural footnote here - is the upcoming California law which promises to ban all gas-powered "Small Off-Road Engines" in lawn equipment by 2024 - see this discussion on "Now you Know" on the reasons for and implications of this. Their sources and calculations for the data below:

The reasoning behind this law is that, in an hour of use, something like a gas-powered leaf blower emits the same quantity of pollutants as the average car does in an 1,100 mile trip; small engines are, in fact, highly polluting - and there are more of them than there are cars. SORE engine emissions in California are approximately equivalent to 1 trillion driven miles per year (about 3 times further than all the cars in California actually drive).

The video talks about the economic savings that can accrue to companies who ditch their petrol motors for electric ones - and somewhere way down the list of advantages - there are some facts about jerrycans - there are 100 million of them in the USA for example, 17 million gallons are wasted annually just from spills when filling them - and they lead to hundreds of house fires and flashback explosions.

The large pollution savings that can be made by a state or country in following this route - together with the savings that landscaping businesses can make by going to electric - mean that this is going to be a compelling law for other states and countries to adopt ASAP. And that will mean, I suspect, that the sort of people who proudly tie their jerry cans to their car bumpers - will be doing so with the militant zeal of a people under threat!
posted by rongorongo at 2:26 AM on October 18, 2021 [4 favorites]


This is a solved problem. Modern safety-overkill vented Jerry cans are *very* unlikely to explode even in a severe impact or puncture, absent a source of fire. And it’s unsafe to keep them inside the vehicle. And sometimes you need gas when you’re not on the road.

Of course the better solution is to own an actual pickup truck, so your gas is both outside the passenger compartment and well protected by metal. At any given time you’ll find 5-10 gallons of gas in the bed of mine, carefully strapped in towards the middle of the bed. And yes rotating it is a pain in the ass but it beats running out of fuel. The biggest risk actually comes from a partially empty can that allows vapor to build up, as vapor is the far more flammable state, so the proper technique is to only carry full cans. Metal cans can be purchased with “flame arrest” technology for heavy duty purposes.

There are millions of Jerry cans out there being poured billions of times a year, and all of them get driven from at least the point where the cans are filled. How often do you hear about one exploding? Used properly they are very safe. Almost too safe, as the venting spout designs in use are almost universally regarded as a pain in the ass by those of us who use such cans.
posted by spitbull at 4:02 AM on October 18, 2021 [8 favorites]


Needless to add but I will: never ever ever carry gasoline in anything but an approved modern gas can. Period.
posted by spitbull at 4:10 AM on October 18, 2021 [3 favorites]


Came here to say mostly what saeculorum did: despite what TV and movies tell you, in most situations gasoline isn't all that explosive. Gasoline vapor can build up pretty badly in containers and if you drop a match into an otherwise enclosed half-full container then you'll get an impressive and possible destructive boom (made considerably worse by the fact that in rupturing it will probably fling burning gas everywhere), but it's not like in the open (which would be the scenario after, say, a jerrycan gets crushed in a collision) gasoline + flame = explosion. More often, gasoline + flame = lake of burning gasoline, which is still, admittedly, a bad thing from a safety perspective but typically a lot more escapable.

The chemistry of the thing: combustion requires both oxygen and fuel. Other than on the surface of gas in liquid form, there's not a lot of oxygen, so that only the top of the pool will burn off. Under the right conditions (I do not suggest you try to do this, because of vapor) it's entirely possible to submerge a burning object in gasoline and extinguish it. For a combustion to cause an explosion, it has to be very rapid and preferably contained, so that the expansion of the combusting material is fast enough to produce a pressure differential and a blast wave. The most dangerous forms of gasoline are aerosol and vapor, precisely because they possess high enough air/fuel ratios to combust rapidly and explosively.

Incidentally, the vapor issue means that, somewhat counterintuitively, the fuller a gas can is, the less of an explosion risk it is, because there's less room for vapor buildup.
posted by jackbishop at 6:05 AM on October 18, 2021 [3 favorites]


Re: the two guys on video spelling out the dangers of gas cans while promoting Tesla: more people have died in battery (and subsequent house) fires caused by BEV battery faults or post-accident ignition in the last five years than have died of “flashback” explosions from pouring and house fires caused by stored gas. Neither one amounts to a significant personal safety risk as long as one takes all required precautions with the technology involved. Like both are more likely to kill you than Ebola in the US, but a lot less likely than a relatively rare cancer. I’m 100% pro-BEV and use almost exclusively electric power yard equipment, and fully concede the ecological case for deprecating gasoline, but risk assessment is a science. And there are use cases where gasoline and its dense energy storage is the best solution for the job, which very much includes taking a vehicle off-road. Or a chainsaw, as for woodland firefighting purposes.
posted by spitbull at 6:39 AM on October 18, 2021 [2 favorites]


Way off topic but I do sorta think that I read this fact in an old linguistics/semantics book by S. I. Hayakawa - Wikipedia. A "Empty" sign placed above the storage for empty fuel containers was a non-minor force in industrial accidents. You see, the empty can is full of that fuel-air mixture that a spark can make go boom, a full can is much less actually dangerous. The "Empty" sign gave people a wrong sense of the security/danger involved. Random Ted talk.
posted by zengargoyle at 11:37 AM on October 18, 2021


Well I’ll continue the derail if mods will allow, because how often does a linguistic anthropologist who’s also a gearhead get to strut his stuff? *

The famous linguistic example of the semantic force of words involving gasoline drums labeled “empty” when they were in fact “full” of deadly explosive vapor instead of safer liquid gasoline was in fact the great Benjamin Lee Whorf (1897-1941), who began his career as a fire safety expert for an insurance company and went on to help craft the theory of linguistic relativity. Hayakawa no doubt tells the story as it’s one of the most canonical anecdotal examples in linguistics, albeit Whorf is exceedingly poorly served by the way he’s usually

*not often, but mods, feel free to delete of course
posted by spitbull at 2:46 PM on October 18, 2021 [1 favorite]


“the way he’s usually TAUGHT.”
posted by spitbull at 3:23 PM on October 18, 2021 [1 favorite]


Ha, I'm wrong but to be fair it was like 27 years ago when I was reading tons of linquistics books. They all sorta blend in together. I'd guess Whorf is also the safety: make the fans blow out just in case they blow up and throw sparks, better have the air carry them outside than inside.
posted by zengargoyle at 4:51 PM on October 18, 2021 [1 favorite]


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