Need to make a hole in a big steel diesel tank. I would say it has 5000 liters capacity, and it should have at least 2/3 filled or more.

Metal Sheet: At least 3 mm thick.

Drill hole is 1" or 2", not sure. It's for an ultrasonic meter.

Problem is if I go drilling, all the swarf can get into the diesel. Second problem is to avoid blowing myself up.

How would you do this?

This is a true case, not an academic question.

About diesel flammability, this is not the first time I hear something like: it's diesel, you can light a cigar with a propane torch while drilling it

These are similar installation, most of them had detachable parts or had a NPT thread built in already.

Plastic Tank

In Tank

On Cap Red Tank

  • 2
    Is the hole going to be above the diesel (top of the tank) or below the fuel level? I'd be tempted to place something on the inside of the tank, opposite of where you are drilling, to catch the metal shavings and isolate the diesel from your drilling.
    – BMitch
    Commented Aug 7, 2014 at 1:30
  • Does the outlet have any type of filter on it?
    – Comintern
    Commented Aug 7, 2014 at 1:32
  • 1
    Also, the CO2 suggestion in the linked thread is a good one, CO2 is heavier than air and should remain in the tank to cut the O2 supply.
    – BMitch
    Commented Aug 7, 2014 at 1:32
  • 6
    Where is the "no oh god no please don't no don't even no no no" button?
    – Yakk
    Commented Aug 7, 2014 at 19:27
  • 1
    Diesel has one of the lowest LEL(lower explosive limits) .06% when compared to a long list of combustibles. Auto ignition is over 210degrees. The incredible explosions using diesel are when mixed with other materials with high LELs. Having attended several fire fighting schools they almost always show the demo of throwing a lighted match in to the diesel can with a fizz out. It is common where repairs can not be made to clean tanks to use a sweep gas, an unreactive gas such as nitrogen or argon to dilute the explosive gas. Ideal is to drain, use a sweep gas, drill, flush and fill. Commented Sep 18, 2016 at 19:17

8 Answers 8


You don't want to "drill" a 1" hole in 3mm sheet. Without support the edge would be ragged and other problems would occur, such as fragments dropping into the tank.

The best approach is probably to use an annular grinder. They are used for putting holes in tile and glass. Search for "diamond hole saw" on Amazon. Use a lot of water to cool it and the slowest setting on the drill. Take a lot of breaks to avoid heat build up. As long as you are using a stream of water to flush the cutting area, no significant amount of metal dust will get into the tank.

The main problem is the chance that the slug could fall into the tank after you cut through. If the surface of the tank is curved, you will not break through all at once, so you just grind until there is only a little bit of connecting metal left, then grasp the cutout with a pliers and work it loose. File to smooth.

If the surface of the tank is flat, then avoid breaking through by cutting 90% of the way through, then bevel the saw (tilt it a little). This will cause it to go through one side first. So you just gradually adjust the tilt, cutting through more and more until you can work the cutout loose with pliers.

Don't worry about small amounts of metal filings in the tank, thats what fuel filters are for. If you attach a neodymium magnet to a cable or rod (STRONGLY) and drag it around the bottom of the tank you will find it picks up all kinds of metallic fragments and junk.

  • 3
    @jacktrades I just mean if you put a magnet in the tank, you have to make sure it is very securely attached to the line or rod, otherwise it will come off and get stuck to the botton of the tank (does it sound like I have done this before?). One thing I have done is use a nitrile glove. You cut off a finger, put the magnet in the finger, attach the line, then wrap the thing with a lot of wire until there is no way the magnet is getting loose. The nice thing about this strategy is that once you peel off the nitrile, the magnet is clean, all the junk is stuck to the glove. Commented Aug 7, 2014 at 15:35

Seriously: You just don't.

  • You'll never be able to guarantee you didn't contaminate the fuel unless you clean it thorougly after the work, which you cannot with all the diesel in there. That bears great (financial) risks. If you sell that stuff you might even get sued. Special drills and precautions will surely reduce that risk, but it will still be there.
  • Any hole added after the tank has been varnished / coated damages that layer and the walls of the hole are naked as well. That is a starting point for corrosion. There is a reason coating is the last thing to do in such constructions.
  • Finally: Would you rely on statements such as "Diesel has a high flaming point" or "use argon on the empty part, to suppress fire"? With your Life? Really?! If someone told me to drill into so much as a tin can filled with diesel, I'd tell em to have fun trying themselves. In you case 3500L. Obviously Diesel is not an explosive so the effect is different but just for the giggles I did some math: The energy in that tank is equivalent to about 340000 kg of TNT, yep 340 metric tons.

Solution: Hire a professional to do the job.
They know what they're doing and they bear the risk and liability.
There's a reason they're called professionals.

  • 1
    Of all the things that could go wrong, the impact of the gas on the health is the least concern. Nitrogen, CO2, nor argon are toxic... unless you stick your head inside the oxygen deprived tank.
    – Davidmh
    Commented Aug 7, 2014 at 16:18
  • @Davidmh well that and cold burn. Plus dangers from storage and usage. User must be very careful in any case
    – Mark
    Commented Aug 7, 2014 at 16:51
  • Okay in my defense, the argon idea was like: if, in the interest of science, you had to drill a hole in a tank full of flammable liquid, how would you do it? And as far as the risk to life and diesel, Argon is used to top off opened wine bottles to keep it fresh so I think, relatively speaking, its an acceptable risk.
    – user23534
    Commented Aug 7, 2014 at 23:43
  • 1
    Over the years have read of many persons killed by entering inert gas or other oxygen-free zone. Please do not do this with the gases. Please do not take any of the advice about 'safe' or 'clean' or 'empty tank = explosive vapor" ways to do this. Hire a professional very well experienced in tanks and such additions, is the only safe way I can think of. The oil companies no doubt use such. Commented Aug 8, 2014 at 8:44
  • @narration_sd actually that is the best advice.
    – Mark
    Commented Aug 8, 2014 at 8:47

Okay I'm going to start this with a giant disclaimer in capital letters: DO NOT DRILL HOLES IN TANKS CONTAINING 3300 LITERS OF DIESEL FOR THE LOVE OF GOD.

Having said that (and hoping that your asking this question purely for academic reasons) i would say: start by filling the empty space above the fuel with argon, its the fumes that burn not the liquid, so if you drive out the oxygen and fumes with an inert gas it will mitigate the chances of an explosion. Then place large welders magnets all around the spot to be drilled to help catch the swarf, lastly use a fresh holesaw at slow speeds to help keep sparks to a minimum. You would want to test this method on a small scale model first. This MIGHT provide a safe way to cut that hole or it might result in a spectacular fire ball.

Just drain the tank.

Here's an exerpt from the Cat Website:

"Diesel fuel is commonly used in construction machinery, industrial machinery and generators. There are three primary concerns associated with diesel fuel:  Flammability: Diesel fuel is not nearly as flammable as gasoline or other common fuels (such as ethanol or propane) but it can catch fire and can be very difficult to extinguish. Do not smoke around diesel fuel. "

  • And be sure to have the plug/valve/bung ready to insert...
    – DJohnM
    Commented Aug 7, 2014 at 1:04
  • I was afraid you'd say that,,,just don't blow yourself up I'll feel really bad:(
    – user23534
    Commented Aug 7, 2014 at 1:06
  • 1
    Again its the vapor you have to worry about not the liquid. Anything atomized well enough is flammable, including diesel. If the concentration of vapors in the tank is high enough (say its a hot day, throw in some agitation if its a mobile tank?) it will be flammable. I've seen wood dust burn like gasoline under the right conditions. Personally I think its pretty irresponsible to advocate not exercising caution in a situation like this. See addendum to my posted answer.
    – user23534
    Commented Aug 7, 2014 at 2:42

User assumes all responsibility! Adding CO2 to displace the O2 sounds like a reasonable precaution.

Use a knockout punch from Greenlee. Quite pricey though, do not buy a cheap one. Good up to 2.5 mm (10 gauge), meaning it's not going to like 3+mm but it will probably work once. Advantage is you only have to drill a 1/4" or 1/2" hole. This does require access to inside the tank to screw on the punch.

enter image description here

Depending on the curvature of the tank you may dimple it. This is not applicable in all situations.


Drilling down from the top is going to make it difficult to keep all of the tailings out. Having never done this myself (couldn't pay me enough), I can't speak to the safety of drilling into a partially filled diesel tank. What I can say is that I know others have done this and that diesel has a significantly higher ignition temperature than gasoline, and it doesn't vaporize as easily. That said, I'd try to keep the heat down to a minimum and avoid sparks.

The way I'd go about keeping metal from dropping in and temperatures low would be to use a hole saw with a fairly small pilot bit. Slather the drill bit in grease and then drill through another big blob of grease and keep the saw ring lubricated. Go slow and wipe off and replace the grease as needed. This should pick up the vast majority of the tailings from the pilot. Run the hole saw down until you are just about through (the thinner the better), stop. Finish up by tearing it out like you would a knock-out.

  1. Diesel gases ARE flamable and explosive. An empty tank that has not been cleaned up internally from diesel residuals is a bomb. There was a serious accident in the news last year when two people went to examine a tank with a lamp (with a naked flame). When drilling steel, sparks might be created and ignite the air-gases mixture.

  2. You CAN'T use magnets (as others suggested) to pickup the remainings when drilling a hole on a steel tank. Both the magnet and the iron particles will stuck on the tank around the whole, as the area there will be magnetized.

  3. The only 100% safe way is to: [a] empty the tank, [b] clean it internally thoroughly to eliminate any diesel fumes. Make sure there are no more gases left inside, use some strong air blower (blow air inside) to make the gases leave the tank. [c] drill the hole [d] clean again to remove the particles. [d] refill with diesel.

P.S An (extreme) alternative way to drill the hole on a full tank without danger of explosion and without the iron parts getting into the tank, would be to do the drilling [1] totally inside petroleum environment -externally [2] while there will be high petroleum flow from the tank to another small container through that whole for the duration of the drilling process [3] with the hole at a low side point while the tank is full, [4] with a proper construction and equipment to make this process possible. The diesel on the second small container could be filtered out and refill the tank later. This requires a lot of inventiveness, expertise and safe design of the whole process, so I recommend my previous (easy & safe) suggestion.


I would use a hole saw with magnetic base. (you can rent them)

Set the Drill Depth Gage to be just under the material thickness of the Metal so that the drill will stop just before the inner metal surface. Drill Nice and slow and keep some Cutting liquid nearby to keep the hole nice and cool.

Also. the Magnetic base will help to hold the shavings onto the drum.

Drill the Pilot hole before-hand, Cleaning the drill castings often - that's the hole for the hole saw to centre.

Once you have completed the first pass hole saw drilling (ie, you have a concentric hole sawed into the metal, Plop a few neo-magnets (high strength magnets) on and around the cut area and begin to knock out the rest of the material within the cut face. (at this stage a small dremmel could also be helpful)

before you start your knocking, i would tie something into the pilot hole so that you can catch the metal ring that will fall into the tank.

enter image description here

  • These are nice and they do have a high vacuum attachment for pulling all shavings away. Commented Sep 18, 2016 at 19:20

Some random thoughts:

I wonder if it could help things to pour liquid nitrogen over the spot where you want the hole for a few hours before starting (and while you're making the hole) You'd be cutting into a slab of congealed diesel fuel that would hold back the diesel, and collect any shavings...

Of course, the low temp might change the steel strength and brittleness for the worse...

Are there water-jet cutters that can handle this thickness of steel?

  • 1
    Water jet cutters? Diesel and Water...
    – jacktrades
    Commented Aug 7, 2014 at 1:24
  • This is a really, really bad idea. There's an excellent chance that the tank will crack.
    – zwol
    Commented Aug 7, 2014 at 22:45

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