Storing petrol in a metal jerry can - is it better to keep the can partly or fully filled?

[NY]

Given the volatility of petrol, is it better from a safety point of view to aim to keep a petrol jerry can partly (eg 1/4 or 1/2) full or to keep it almost completely filled? Or doesn't it matter? Subject to common sense about not opening a can on a hot day in an enclosed space.

I presume that petrol in a jerry can doesn't "go off" in the way that it is said to go "stale" in a lawn mower petrol tank, because the volatile fractions cannot evaporate.

What is the legal limit of the amount of fuel that can be stored at home (eg in a garage)? I've seen some sites which say that only 5- and 10-litre cans (plastic or metal) are legal, and that 20-litre metal jerry cans are not legal, even though the storage limit is a total of 30 litres: the implication is that three 10-litre cans is OK but one 20-litre can and one

10-litre can is not. Others say that 20-litre cans are fine, though it may not be legal (*) to fill them at a fuel station, and that fuel must be bought in 5- or 10-litre cans and then transferred to the 20-litre can.

Are the storage restrictions the same for petrol and diesel?

Given that plastic cans are 5 litres and many garages will not dispense less than 5 litres, it means you have to run the can right down until it is empty before you may refill it - or else have a second can into which a partly-filled can may be emptied so the first can will take the full 5 litres. I had to take care when writing that sentence to avoid the confusion between the noun "can" as a storage device and the verb "can" meaning "it is possible to" ;-)

contains a very weird paragraph. It talks about the maximum amount of fuel that can be stored without a licence, and the permissible containers (20 litre can is fine). But then it says "If you do not have a licence to store petrol, you should not dispense petrol into the tank of vehicle with an internal combustion engine, either by manual or electrical means." So you are allowed to store up to 30 litres, but you are not (apparently) allowed to fill your car or your lawn mower from that can? WTF! Maybe "dispense" has some special meaning that doesn't include pouring from can to fuel tank.

(*) Or some filling stations may not allow it.

[Andy Burns]

If the can stores the same fuel as any of your cars, simply top-up the can at the same time as the car.

[Dave Liquorice]

Assuming the container is sealed, yes.

I think 5 litre containers can be plastic or metal. 10 litre metal only.

AIUI 20 litres plastic or metal is not legal for petrol.

No. Petrol is very volatile stuff, the vapour can easyly build up to "whumpf" levels if not explosive. Diesel takes quite a bit to get going, as in burning with a flame, even when on a wick of some sort. IIRC you can store around 500 l of diesel in a tank. Probably have to be bunded these days.

It might be the HSE site but I doubt that 20 litre container is correct. What is the context? Home garage attached to house, or some other building close to house or further away? It's a while since I looked at the regs/licencing conditions so maybe getting muddled about buildings between petrol and diesel.

A lawn mower isn't a "vehicle". B-)

Quite possibly but it does seem very odd. Maybe written by someone who knows the rules backwards and has read what they though they wrote not what they did.

[newshound]

From the safety point of view, the safest option is to keep it empty.

The less you have in it, the less the possible consequences of a leak and fire.

Subject to that, it makes no practical difference. Unless you manage to fill it up completely with no vapour space at all (in which case expansion of the fuel will stress the can if it heats up) then the pressure in the can depends only on the temperature of the fuel.

It all depends. With the normal type of rubber seal, there will be some diffusion of vapour through the rubber, and in general the more volatile compounds will diffuse faster. So the strict answer is that the composition will change with time. In practice, the effect is likely to be negligible. Depending on the type of rubber, over years or decades the seal may degrade by oxidation from the outside and eventually the seal may fail.

[The Natural Philosopher]

i've got a 2500 litre heating oil tank

[alan_m]

Your fuel filler cap probably has a vent (hole).

Use an additive

Do you have a car? If so, any amount into the can and the rest in the car's fuel tank.

Who do you think is going to be knocking at your door if you have a large can of petrol or multiple cans (metal or plastic)?

[The Natural Philosopher]

The loss adjuster if you have a fire.

The police if someone gets hurt from it.

[williamwright]

I don't understand how that would work. You turn up at the filling station, put 4 litres in your can, replace the hose thingy, read the amount, go in and pay. Do you mean they'd ask for the money for 5 litres?

Bill

[NY]

I've always wondered that. I presume its related to the accuracy of the metering in the pump, and that an absolute error will be a greater proportional error of the total amount of fuel sold.

My local garage still does attendant service rather than self service. I was impressed that the attendant managed to dispense exactly 5.00 litres at full speed, without having to slow down as he got close to the limit, dispensing the last amount "drop by drop" until the pump read exactly 5.00.

Reading more about it, there is a difference between the nominal capacity and actual capacity of a can, and that cans have about 30% extra space to allow for thermal expansion - or to allow 5 litres to be dispensed into a can that already has a bit of fuel in it.

[Dave Liquorice]

Snap and kerosene is more volatile than diesel but nothing like petrol.

[newshound]

Yes. You accepted their terms and conditions when you started the pump.

[NY]

Yes, that's what I've read on some sites. Others such as

and the HSE site mention 20 litre jerry cans as being legal.

But legal for diesel?

Odd that an official site like

contains misleading info about what the law does and doesn't permit.

[quote] Requirements for keeping up to 30 litres of petrol in suitable portable containers or in a single demountable fuel tank

1. A person keeps petrol in accordance with this paragraph if-

(a)no more than a total of 30 litres in suitable portable containers or in a single demountable fuel tank is kept, of which-

(i)no more than 30 litres is kept in one or more suitable portable containers;

(ii)no more than 30 litres is kept in one demountable fuel tank; or

(iii)no more than 30 litres is kept in no more than two suitable portable containers in any motor vehicle, motor boat, hovercraft or aircraft; [/quote]

And Schedule 3 of PCR defines a suitable container as

[quote] A portable petrol storage container must-

(a)have a nominal capacity -

(i)no greater than 10 litres if made of plastic; and

(ii)no greater than 20 litres if made of metal; [/quote]

That looks to be the definitive statement.

I wonder if the confusion about the legality of 20 litre cans is related to different regulations for *buying* petrol at a petrol station (where I'm sure the 2x 5 litre or 1x 10 litre restriction does apply) and *storing* of the bought fuel at home (when *maybe* it can be decanted from a 5 litre can that it was bought in into a larger 20 litre can).

What we will need to bear in mind is the *total* amount: we were planning to keep one jerry can each of petrol (for the mower) and diesel (for our cars - in case we get home with very little fuel and need to top up until we can conveniently fill up at a petrol station). That would be a total of 40 litres (since we have a two 20 litre cans) so we'll need to take care to only partly fill each can. I wonder if that word "petrol" is crucial: maybe we are allowed up to 30 litres of petrol, plus a larger quantity of diesel.

In our case, the garage is a separate building about 3 metres at the closest point to the house.

Some people race lawn mowers, and that context they are vehicles - but that's a *very* specialised case ;-)

I found

which says "petrol is not dispensed (ie it is not pumped either manually or electrically from a storage tank) at your storage place". I'd taken "dispensed" to be a nice vague wishy-washy catch-all term which included both pumping and pouring, but it looks as if it specifically means "pumping", and that the restrictions do not apply to pouring. Getting picky and pedantic, I wonder if their definition of "dispensed" includes gravity-fed ;-)

[Andy Burns]

Minimum delivery was 2 litres last time I took any notice

[Martin Brown]

And bone dry without any trace of petrol vapour in it!

But the most dangerous petrol fume explosion if there is a spark. Petrol air mixtures are explosive over a very wide range of composition.

It is marginally safer to have mostly fuel in the tank provided that you are not likely to knock it over. It is the petrol vapour that tends to flash if it manages to creep along the ground to a source of ignition.

You can see the petrol vapour when pouring petrol into a lawnmower in sunshine by the effect of its refractive index in the air on the shadow.

The stuff still ages in contact with air forming various polymeric gunk which slowly plates out inside the container. It isn't a good idea to keep petrol for too long as the volatiles always find a way to escape.

I keep it from one season to the next for my lawnmower & strimmer.

[The Natural Philosopher]

kerosene is *almost* identical to diesel

[charles]

A couple of years ago I bought a 20 litre jerrycan for petrol. I filled it back in March. Glad I did it then since I wouldn't have been able to buy fuel for the lawnmower in April or May. There's still some left. I don't keep it in the house.

[NY]

I'm sure I've seen some pumps where that has been raised to a minimum of 5 litres. I only started noticing when we got a petrol mower and there was the problem of the minimum delivery being the same as size of can. No a problem if you've got a petrol car as you can put any excess into the car - but both our cars are diesel.

As a matter of interest, would a litre of petrol in maybe 30 litres of diesel harm the injection pump? Not that I'm contemplating trying it: I'm always scrupulous about making sure I don't mis-fuel. Which is worse: petrol in a diesel car or diesel in a petrol car? I remember when I was little one of our neighbours "decoking" his Morris Minor (ie long before fuel injection!) by putting a can of diesel into the tank every so often. I've seen a motoring programme like Top Gear a test where they tried running cars (about 1990s vintage cars that were destined for the scrap yard anyway) on the wrong fuel, with a lot of spluttering, chugging and clouds of smoke from the exhaust.

[John Rumm]

ISTR most of the pumps round here say something like "minimum delivery

2L"... so not a problem with any typical can.

(personally I just fill the can till full, then carry on with the car. That does mean the lawn mower gets super unleaded sometimes, but it does not seem to mind!)

[Davey]

From the Driving License website:

"Other categories Category Vehicle you can drive f Agricultural tractor G Road roller H Tracked vehicles k Mowing machine or pedestrian-controlled vehicle

et alia.

[NY]

When I got my first driving licence, I was surprised what *other* vehicles I was allowed to drive (even if only provisionally), apart from a car.

I'm always surprised that an ordinary car licence allows you to drive an articulated vehicle such as a car towing a trailer/caravan without any proof of additional tuition (let alone a test of competence), given the fact that being able to reverse an articulated vehicle is a whole new level of skill (and one which still completely and utterly defeats me). I think nowadays there is a weight limit on the caravan for a normal licence, but that still allows you to drive a trailer or light caravan without additional test, so it still assumes that you will "magically" be able to reverse competently. Actually I imagine that a caravan is easier than a small trailer because a) you can't see a low trailer when it is directly behind you, only when its rear end turns to one side or the other; b) the trailer has its axle much closer to the hitch than a caravan does, so the "gear ratio" for the steering is much higher: a small movement of the rear end of the car causes the trailer to swing much more than a longer caravan would.