Neil McRae a wellknown and respected collector of pressure lamps did some research and comparisons.
Exploding the Petromax Myth
The ensuing discussion was most interesting and brought to light some facts I was not until then aware of. This question of an exploding lantern has been occupying my thoughts ever since and I now have a much better understanding of the design of a Petromax lantern and whilst I cannot be sure exactly why this lantern went bang I do know why gasoline and Petromax do not go together. What still amazes me is the fact that we do seem to have a lantern that was designed to blow up customers and it has been around for over 50 years.
The exploding lantern that sparked my interest was almost certainly a Hong Kong made lantern sold in the US as a Petromax brand lantern. I do not know which US company sold the lantern but in a reply to some of my questions the owner stated "The lamp was brand new, purchased in the United States on 11 October 2001. The lamp was used twice, with the accident occurring on the second occasion, on 27 October 2001, after burning for about four hours. The retailer indicated any fuel was appropriate, but white gas was used on this lamp. The pressure gauge was not read immediately prior to the accident. By "exploded" I mean there was a loud "Whooomp" sound and the entire tent (a large tent) was temporarily consumed in a large ball of fire" . If the retailer is the one I think it may be then the instructions do indeed state that the lanterns can be run with either kerosene or white gasoline.
One of the "facts" I learnt from this discussion was that in or around 1960 the German army had banned the use of gasoline in their Petromax lanterns. Rumour has it this ban was because significant numbers of these gasoline lanterns had suffered catastrophic failure in use. If true that was significant as the German army version was model number 829B and the B signifies the lantern is designed to use Benzin or Gasoline. I was told that prior to the ban several army lanterns had failed and the army were trying to make sure the more volatile fuel was not used. Now that introduces a whole new dimension. A failure of a Chinese lantern might be possibly due to poor construction but regular catastrophic failures of German made lanterns designed to use gasoline in the late 50s when Petromax were actually being made in a German factory has to be a design problem.
Right there is where I began to look at the design of gasoline lanterns and in particular to look at Petromax design.
The first problem I had to resolve was to set about acquiring one or more gasoline burning Petromax lanterns in order to compare the design with the more normal kerosene lanterns in my collection, of which I have many, including a lot of Far Eastern made Petromax copies. I now have a Swiss army Petromax 250cp gasoline lantern which has no model number but is essentially model 821B with a larger fount as fitted to 500 cp lanterns. I also have a Bundeswehr model 829B made in the Altena Petromax factory in May 1960. After dismantling both lanterns I found that apart from a different generator and gas tip the design of these gasoline lanterns is exactly the same as the more familiar kerosene lanterns. The only difference being the substitution of a generator built to use the more volatile fuel.
The instructions for the Swiss version states the fuel to be used is benzin (gasoline) and no mention is made of the possibility of using kerosene. The German lantern came with the correct army issue steel case and the instructions. Both the instruction decals on the case and the leaflet state the preferred fuel is Benzin (gasoline) but that Petroleum (kerosene) can also be used.
In each case the reference to the use of benzin has been crossed out and there is a decal on the fount stating "Nur Für Petroleum. Verwendung von Benzin verboten" This roughly translates as "Only for kerosene. The use of gasoline is forbidden" So this gasoline lantern has army instructions to use only kerosene and that reinforces the statement that the Bundeswehr banned the use of gasoline in these lanterns. I should perhaps at this juncture point out that here we have a hugely successful lantern that has been copied all over the world and has been sold in vast numbers in most countries. The Petromax kerosene lantern is perhaps the most successful piece of pressure kerosene lantern design by a considerable margin. However that design seems to fail when gasoline is used so what is wrong?
Let us then look at the design of a Petromax in some detail with particular reference to it's suitability for burning gasoline.
The founts are made of brass with a lead solder base seam and lead solder seals for the upper fittings such as the valve unit, filler cap, central fixing point, and pre heater blow torch if fitted. A lot of Far Eastern copies have steel founts but this is not significant. The valve and blow torch units are screwed into the fount and use a lead washer to make a seal. The filler cap is normally provided with a pressure gauge and a pressure release valve and is sealed to the fount with a synthetic rubber sealing washer.
The control valve unit performs two functions. It operates a tip cleaner rod which runs through the generator and has a needle at the top to clear any blockages in the gas tip. It also operates another rod, which passes through the fuel pick up tube, to open and close a valve mounted at the bottom of the fuel pick up pipe located near the bottom of the fount. This lower valve is a spring loaded rubber seal unit much like the check valve in a Tilley or Primus stove pump tube. The two rods are arranged on a cam so that when the tip cleaner is in the clean or raised position the valve will be closed by the action of the spring forcing the rubber seal against the orifice in the bottom of the fuel feed tube. When the control wheel is rotated a half turn the tip cleaner is lowered and the lower rod pushes the rubber seal back from the orifice so fuel can pass. The pump provided is a simple tube angled down towards the bottom of the fount and again has a spring loaded valve in the same style as a Tilley or Primus stove valve. This valve is therefore located in the fuel when the lantern is in use.
There are other design features that make a Petromax look the way it does but they don't concern us much here, except perhaps with air flow patterns, because they are only to do with mixture and the upper parts of the lantern where the fuel is already vaporised and burning. What I am looking for is reasons for fuel burning where it should not. Let us look at the design in detail then. First the use of lead solder and lead seals in the fount. Lead solder melts at around 550 to 800o C and as most of you will know that is a comparatively low melting temperature well below that of a candle flame never mind a pressure lantern burner flame.
Is this important? Well maybe it is. Like a lot of lanterns the mantle in a Petromax hangs down from the burner. Petromax mantles are sewn with a gather at the bottom and it is possible for there to be a small hole at the lowest point. Therefore it is possible to get a spike of flame vertically down from the mantle. This flame can reach the top of the bolt which holds the globe cage in place. The lower end of this bolt is screwed directly into the top of the fount so it is possible to heat the top of the fount with conducted heat through the bolt, maybe to the melting point of the solder and lead seals.
Incidentally I suspect this conducted heat through the bolt, or even down through the valve casting, is the major cause of all those exploding lanterns. I said earlier that the upper parts of the globe cage and hood are of little concern here but there is one design feature of these lanterns that affects heat transfer around the top of the fount. Most pressure lamps take air for combustion from within the globe cage, or below it through holes provided in the support collar. Such an air intake at low level provides a flow of cooling air across the top of the fount.
In a Petromax design the air intake is through the lower series of holes in the hood and the products of combustion are vented through the upper vents. The two parts of the hood are separated in use so the products of combustion do not affect the fresh air intake. Therefore any heat conducted through the metal parts down towards the fount are not cooled in any way which may be a contributing factor to the possible failing of the lead or solder seals.
It is also interesting to see that most modern Petromax lanterns are now fitted with an extra heat deflector plate which protects the holding bolt from possible over heating from a damaged mantle. This very late, possibly 60s design, plate is visible evidence that the manufacturers recognised a problem and were attempting to reduce the risk.
Now a look at the control and fuel supply. Spring loaded valves will fail in time. This is not a possibility it is a fact. Rubber seals will wear out and at some point require replacing. In the Swiss army lantern I found the valve did not close off the fuel supply so the operation of the control wheel only reduced the fuel feed through the gas tip but it was not sufficient to turn off the flame at the mantle. I therefore had a lantern that would not turn off and this is not good news. If there is a problem it means the lantern cannot be turned off and the only steps you can take are big quick ones. In a kerosene lantern this is no problem as you can just dump pressure by opening the pressure release or removing the filler cap. Not a great idea with gasoline in the fount so close to a burning mantle. This is possibly not so very dangerous because the release valve vent is a small hole and a flash back into the fount is unlikely. However this is not a theory I want to test.
Staying with spring loaded valves, the same sort of problem is found in the pump tube. The seal in the valve will fail at some point. It is in the nature of the beast that now and then you will get a discharge through the pump tube. A Petromax pump check valve discharges air directly into the fuel at the bottom of the fount. It is therefore inevitable that when the valve fails raw fuel will discharge back up the pump tube. I have twice now had a kerosene lamp vent a fount full of fuel through the pump tube. With a kerosene lamp this makes a mess but with gasoline would have been a serious and exciting incident.
Next is the filler cap and it's pressure release. The cap itself is fine but a pressure release in a gasoline lantern is a poor idea because you might be tempted to use it to turn the lantern off and I don't think it is a great idea to release gasoline vapour within six inches of a burning mantle. Finally I would like to compare Petromax design with just about any Coleman gasoline lantern. This comparison makes the design of the Petromax when used with gasoline look very poor if not dangerous.
Coleman founts are generally not sealed with lead solder. They are copper brazed and will not fail when heated. All the fount top fittings are screwed into the fount with a tapered brass thread with only a small amount of thread sealer which will not be affected by heat. Also Coleman lanterns nearly all take air for combustion from below the base plate and through the collar which provides a gale of cooling air across the top of the fount. Coleman and most other American gasoline lanterns have a positive needle valve fuel shut off. None of these lanterns rely on a spring loaded valve to do this job. That feature of a Petromax is strictly a European kerosene product idea.
Only a few Coleman Kerosene lanterns are fitted with a pressure release valve in the filler cap. None of their gasoline lanterns have this feature. Similarly with pumps, only a few kerosene models have a Petromax type of European pump check valve. All the gasoline products have a double check valve with a steel ball valve and then a screw down needle valve. Also typically from the bottom of the pump tube there is a tube leading up to the top of the fount so that even if the valves both fail there will be no fuel discharge. Such failure will only vent the fount of air and therefore a pump failure will just stop the lantern burning due to failing pressure.
My conclusion is that there is no Petromax or Petromax type of lamp or lantern that is safe to use with gasoline as fuel, even if the company designed the burner to use such fuels. They are good reasonably safe lanterns with kerosene but with gasoline or similar fuels are quite literally gas bombs just waiting to demonstrate what bombs do best. Incidentally these design features have persuaded me to the opinion that even with kerosene this type of lantern is not good engineering design.
© Neil A McRae
First published in Light International Vol 6, issue 3, Summer 2003.
Text with pictures as PDF downloaden.