Tilley FL6 explosion.

Tilley FL6 explosion 30th July 2011

I was contacted earlier this year by the lawyer acting for a lady who had been badly burnt in the fireball from a lamp that had exploded during a private social event in Peggy’s Cove Nova Scotia on Saturday July 30th 2011. I was provided with all the witness statements taken by an investigation agent for the lawyer.

The event was an annual pig roast which had been a regular event for some years and attended by about 50 or so relatives and friends of the host.

The lamp in question is a Tilley FL6 made sometime in the 1950s. It was mounted on a tripod which is not a Tilley extending type but made of grey painted wood and is possibly a Danish Civil Defence issue type. The lamp was about 6 feet above ground with the controls at about head height.

As it became dark the host of the event lit a Tilley FL6 mounted on a tripod to illuminate the area. After some time the lamp began leaking fuel which was burning as it flowed over the tank of the lamp and dripped onto the ground. One of the young ladies present attempted to extinguish the flames by throwing some water over the lamp and ground from a bottle of water she had been drinking from. When the bottle was empty she turned away and as she did so there was an explosion and a big ball of flame which engulfed her causing severe burns. She was rolled on the ground by some nearby people and the flames extinguished before she was taken to hospital. Although badly burnt she survived the incident. I don’t have details of the injuries sustained but in May 2016 the insurance company paid out compensation of $500,000 which may indicate the severity and long term effects.

The host of the party indicated that he went to try to shut the valve off before the explosion but was unable to do so as the flames appeared to be leaking out of the valve itself. There had been some fire extinguishers in the area earlier in the day but at the time they seem to have been removed because none of the witnesses recall them being anywhere near and they were not used in this incident. One of the witnesses also attempted to turn the lamp off but the burning fuel prevented this and the lamp’s owner went to either get an extinguisher or a glove to enable him to access the valve but in the event this action was too late to prevent the explosion.

This is an image of the lamp taken a few days after the event which clearly shows the base plate has been blasted open by a considerable internal pressure induced force.



Below is my report and conclusions which I submitted to the Lawyer on the 8th April 2016.

Dear Mr _________

Re Tilley incident 30th July 2011

I am Neil Arthur McRae aged 73 a retired civil engineer since 1999 and former Contract Manager for the local water supply company in Hertfordshire England. I am a director of the International Guild of Lamp Researchers Ltd. Directors of the Guild are selected only from the members who are most active and experienced and membership is restricted by invitation only to those people who are experts in their field and proven researchers. My speciality is historic liquid fuelled pressure lighting of the 20th century. I research both the lamps themselves and the companies and people who made them. I am not the only pressure specialist on the board of directors but I am the only English member and the most experienced with English made Tilley lamps. I am also a founder member of the web site http://www.classicpressurelamps.com/forum/index.php? Established in 2010 with user name Mackburner and frequently post answers to identification requests and technical questions there.

I have been collecting, using and researching Tilley lamps and other makes of pressure lighting since 1965. I currently own about 800 pressure lamps including three Tilley FL6 Floodlights. Since Tilley was and is the single biggest manufacturer of pressure lighting in the UK these lamps are perhaps the types I am most familiar with. There are perhaps half a dozen or so collectors within the UK who are as experienced as myself with Tilley lamps but none who are more so.

I have read the transcripts of the investigation reports and statements supplied to me by Guy Farrell and have studied the images of the damaged lamp. I have a good understanding of this incident and of the actions taken by the various people involved at the time.

The lamp.
The lamp in this incident was a Tilley FL6 made in Northern Ireland at some time in the mid 1960s. Tilley floodlight model FL6 was introduced to the product line in 1937 and was in production in the Hendon factory until about 1962 when production was moved to Dunmurry Northern Ireland where the model continued to be made to about 1969. There were during that time some minor changes to the outward appearance but the construction and method of use remained the same throughout the period. FL6 is a floodlight with a 14” parabolic reflector and a 250cp kerosene burner unit. The light is provided with a soft mantle which incandesces at high temperature. The lamp has a fuel container of one imperial gallon capacity approximately 8” diameter and 7” tall. In normal use this container holds 6 imperial pints of kerosene and the remaining volume of air above the fuel is pressurised with a built in pump to a working pressure of 30psi. As the product was designed to normal British engineering and insurance standards this implies the unit was designed to withstand a user test pressure of 60psi and a works pressure test of 120psi. The fuel tank is made of a spun brass body with a flat dish base plate welded to the inside of the rim of the main body with a soft lead solder which provides both a mechanical joint and a fuel/air seal. The normal thrust induced by the working pressure onto the base plate is about 1,500 lbs and the total thrust at works test is about 6,000 lbs. This thrust induces a shear force on the solder seal of the base plate which is designed to withstand the works test thrust and is therefore capable of withstanding a shear force of about 25lbs per inch run of the seam. In fact I would expect the seam to be capable of a much greater shear force of perhaps more than twice this.

In use the fuel is forced through a feed tube to a fitting at the top of the tank. A valve control unit is screwed into that fitting. The valve has a socket at the upper end into which is screwed a vaporiser which is a 7” long steel tube with a 0.007” hole or jet at the top which discharges into the burner unit. The control valve is a dual purpose device which contains a spring loaded shut off valve and also operates with a cam a pricker wire which runs the length of the vaporiser and is used to clear the jet hole if it gets blocked with carbon or other foreign bodies. The valve and pricker control is operated by a spindle which is sealed with a gland nut which is packed with a rubber type seal. There are of course two gaskets either side of the valve between tank to valve and valve to vaporiser.


Cause of the failure and explosion.

I am in no doubt that the failure of the Tank in this incident was the result of the failure of one of the seals at the control valve which caused a leak of liquid kerosene which ignited. It is possible but unlikely that one of the fixed gaskets between tank and valve or valve and vaporiser failed. These seals once installed correctly are not disturbed in use and if they were not leaking when the lamp was lit are not likely to have failed subsequently and I understand that the owner of the lamp had serviced the lamp with replacement seals as they were required so I would assume that these two gaskets were in fact sound and did not fail. The spindle seal within the gland nut however is subjected to intermittent movement when lighting the lamp and possibly also if it is necessary to operate the pricker when the lamp is working. This seal can therefore seem to be good on lighting but can start to pass fuel after operating and rotating the spindle. In fact it is common to have to tighten the gland nut when lighting the lamp or after operating the pricker. This gland seal is normally only just tight enough to seal the spindle. If it is too tight then it is difficult to operate the valve so it is nearly always only just tight enough and has to be inspected regularly because they routinely leak a little and have to be tightened. The gland nut is knurled and designed to be operated by hand without tools although most operators will tweak the gland nut with pliers. In an FL6 this gland nut can be difficult to access because it is within the casing of the lamp and not always presented facing forwards, it is also not always easy to see a leak here for the same reason that it is partially hidden by the lamp casing. Nevertheless an experienced and prudent operator should be aware of this potential leak point and will inspect it after each use of the control. The leaking and burning fuel then flooded over the tank and dripped burning to the ground. The burning fuel on the tank would have heated the air and fuel in the tank which greatly increased the internal pressure to the point where the base plate solder seal could no longer withstand the thrust imposed on it and the solder seal failed. In fact if the tank heated to a temperature where the kerosene began to boil then the pressure would have increased rapidly to an enormous degree. Such heating would also have softened the solder in the base plate seal and reduced its strength. This failure resulted in a sudden discharge of hot fuel and high pressure air. The combination of high pressure air and fuel atomised the kerosene into a fuel/air mixture which then exploded into a fire ball. Cold liquid kerosene will not burn freely but if it is atomised and warm then it forms an explosive mix.

In this case I have to conclude that the operator of the lamp failed to notice that the gland was leaking on one of the occasions he operated the valve. It was not mentioned in any of the text I have read but perhaps the pricker was operated after the lamp had been running for a while. Once the leak and fire was noticed I suspect he was well aware of the danger of the burning fuel but perhaps did not consider the fact that the tank is actually a pressure vessel and that the heat was increasing the pressure to a dangerous degree. However there was one action he could have taken which might have prevented the failure. As the control was not accessible due to the burning fuel it might have been possible to unscrew the pump housing which would have released the air within the tank and the resultant drop in pressure would have shut the lamp off and removed the danger of a pressure failure leaving just some free burning fuel which could have easily been contained and made safe. Was he negligent? Well yes because he was the operator and the lamp leaked fuel after being lit and there was no attempt to release the pressure. Not in my opinion gross negligence as it was not because of carelessness but perhaps he was not as experienced a user as he liked to think nor was he aware of the nature of the beast being a pressure vessel as well as a light and that a pressure tank has its own potential for disaster.

I have considered the suggestion that the small amount of water thrown at or near the lamp by Charleen might have been a contributing factor. This is not credible. These floodlights are Storm Lamps designed to operate in extreme weather conditions and they will happily function in the heaviest of rain storms. In fact it had been or was raining at the time and the lamp would have already been wet. It might have been useful to throw a few bucketfuls of water at the lamp because that might have cooled the tank and reduced the internal pressure but a pint or less would have had no effect at all.

Throwing water onto a hydrocarbon fuel fire is not a good idea as the burning fuel will only float on the water which just enables the fire to spread faster. However this incident was caused by a pressure failure due to the burning fuel from a leak and not by water in any way.

There was a suggestion that there might have been some effect of the water on the metal which helped to exacerbate the failure but I don’t believe this is possible either. As most of the lamps I deal with are made of brass I am familiar with how brass behaves under heating and cooling. Under heat brass can either soften or metals in the alloy. The brass in a Tilley tank will harden and can subsequently crack. Either way heating and then rapidly cooling anneals the metal so restoring its molecular integrity. So in this case adding water was in fact the right thing to do because it might have spread the fire a little but would have cooled the tank and prevented the pressure induced failure of the tank but it was too little to have any effect.

Yours truly

Neil A McRae

 

A very well reasoned and written explanation, Neil. I have a few questions, though:

Would the operating heat in that area of the lamp be enough to vaporize the leaking illumination paraffin as it ran down the fount?

Would it perhaps be reasonable to suspect that a more volatile fuel or mixture was being used?

 

"The fuel tank is made of a spun brass body" - don't you mean steel Neil? Did the FL6 ever come with a brass tank?

I've always suspected these FL6 tanks are a bit dodgy. They have a base plate with a large surface area resulting in considerable downward force, but unlike say a Coleman CQ table lamp, there is no bar running through the center of the tank to support the center of the base plate.

Then the rim of the tank is not rolled over the edge of the base plate like on a Petromax. This means there is only the solder joint holding the base plate in.

Another problem is the FL6 pump cup has a large diameter which helps to pressurize the tank quickly but also allows it to be over-pressurized, as the smaller surface area of the pump on say an X246 lantern limits the maximum pressure that can be achieved by hand pumping alone.

Are we sure they were using Kerosene and not Gasoline in the lamp?

If Kerosene was running down from the control cock washer or vapouriser washer then it should not have caught fire unless it soaked into a wick of some sort on the ground and was then ignited (by what?). Unless I suppose the paraffin was coming out of the vapouriser either from a crack in the vapouriser or because the vapouriser had cooled for some reason and started dumping liquid fuel out of the jet, causing a flare-up that was left uncontrolled.

 

So the only evidence of an exploding lamp is a Tilley.

From what I read was the fuel leak dripping. Not pouring hugh amounts. So overheating is difficult in my idea.

Neil, Do you have proof of the fuel used ?

I have had such an experience: fast increasing pressure with a gasoline filled donut. Luckilly it was not alight. I just re filled a hot lamp.

 

Neil is an intelligent and very experienced lantern user.
I am sure that he will have asked himself all the questions that are posed above.
Neil's statement is a summary of extensive reading of evidence and carefully considered judgement.
Personally I would not question his statements in this legal issue.

 

I have no experience of this lamp so am not qualified to comment, however, as Neil has posted it in the 'Pressure Lamp Discussion Forum', is it not logical to conclude that he is happy for the matter to be discussed?

Terry

 

From my experience the gland nut at the pricker gets hot enough to evaporate even leaking paraffin, and these fumes will ignite easily. I experienced that myself not only at one single lantern. The most annoying effect of this failure is a bad smell while the lantern is lit and the fumes did not ignite.
However, the leak must have been such serious that a considerable amount of burning fuel was sipping on the tank and heating it to cause the catastrophic failure. Assuming paraffin was used, a careful/experienced user would most likely have released the pressure from the tank early enough and that would reliably have eliminated the hazard (which probably would not have been a good idea when using petrol). But obviously that was not the case.
My only advice would be to be extra careful with any kind of fuel which may get hot and is put under pressure. Aerosol bombs are amongst the most destructive weapons.
100% agreement to Neil's explanations, no matter which kind of pressure lantern is used. Soft soldered joints (lead-tin) already get weak at temperatures above 150°C, and the melting point will be somewhat lower than 200°C.
BR, Martin

 

Yes of course we can discuss the matter.

We do know the fuel used was kerosene. I have to hand eight witness statements and some evidence from the injured lady and the owner of the lamp and my report was based on those statements. However I will not make those statements public and I will not name the people involved.

That report was produced fairly quickly as I was under pressure from the legal guy to come up with an assessment so he could make an end to the case. There are mistakes which I have let stand because that is how I reported at the time. The lamp in question was 1950s not '60s and the tank is steel not the brass I implied.

FL6 lamps are unusual in that the valve is contained inside the lamp casing and there is no cooling air flow at that point so it can get hot enough for a leak at the gland to ignite. The witnesses all agree that there was burning fuel flowing over the tank and dripping down to the ground and causing a fire under the lamp on the grass. I must emphasise that I don't know where the leak was. The lamp was never inspected afterwards by any competent person so I had to speculate on the cause of the leak. I believe I have it right but I can't prove it. What I do know is that under normal use a Tilley tank will not fail in this way. The state of the tank in the image shows it suffered a catastrophic and sudden failure which can only be the result of a massive increase in pressure. Heating the air over the fuel would probably not be enough to do this so I assume the kero had started to vaporise. Boil anything in a confined space and you get a high pressure vapour.

So it ain't perfect but there is no argument that there was a fuel leak and that the lamp base failed which caused a seriuous injury to a young lady who has to live with the consequence. ::Neil::

 

Were there any legal and financial consequences for the operator? I hope that the young lady has recovered from her injuries and that she is able to lead a normal life.

 

Very interesting. Was there any report from the person who lit the FL6 stating if they had stopped pumping it up when the pressure indicator reached the top of the collar or indeed if the indicator was working? I know they are not always reliable but am curious as to whether it may have been greatly over pumped up in the first place. Thus exasperating the effect on any seals if the control cock or vaporiser had not been screwed up tightly.

 

I remember reading here a long while back, that there was no need to use two O-ring washers in the behind the packing box of the control cock (as shown in Tilley instructions).

Anyway, as I have bought a fair few of these O-rings fro The Fettle Box, I routinely put two on each control cock.

From first principles it would seem that having two would reduce the risk of leakage (ie two points of compression) - but I'm happy to be contradicted.

As it is, I'll be doubly careful with my FL6s from now on.

Regards

Tony

 

A lesson for us all

From the information given it is possible that it may have been a minor weep of fuel which ignited with the resulting fire causing the seal to fail completely, therefore turning it off may not have stopped the fuel escaping. Cracking open the pump and releasing the pressure, in the same way you would during a flare-up when lighting, may have prevented the explosive failure, or liquid fuel being sprayed out, entering the world of What if, Possibly and Maybe?? How many people here have picked up a lamp or stove after use and found it looking a little damp or sitting in a puddle of fuel?

 

Neil,

Thanks for sharing this, very interesting. Let's hope the lady has recovered.

 

The one witness not interviewed by the investigator is the owner. I have some info from the investigators synopsis of the events but it seems other than determining that the owner was familiar with the lamps and had used them to light up the pig roast for several years there was no detail on how he had operated the lamps on this occasion.

The people concerned , both lamp owners family and the injured lady, were and remain friends. The lawyer was not acting for the injured party but for the insurance company although reading between the lines he was obviously sympathetic to her. Someone obviously made an injury claim to an insurance company but I don't know if it was the owner's or the injured lady's insurance that was invoked. ::Neil::

 

What insurance was it? Home insurance or some sort of commercial public liability?

 

Very interesting read . To unscrew the pump would have been the best thing to do I have done it myself in the past and after a short time lamp goes out.
Simple ,but only if you know how.
FL6 did come with a brass tank

 

I have no idea. I just know the lawyer was acting for an insurance company. ::Neil::

 

interesting read.thanks neil.

 

Although I have been a member for a couple of years this is my first post I would like to say thank you Neil for sharing your report on this incident.

 

Welcome, Jigsaw.

Cheers

Tony

 

Yes I thought it was important that folk should know what can happen when you heat a pressure tank full of fuel. We often forget that the potential for disaster does not only come from the fuel but also from the pressure vessel itself. Reinforces the importance of good maintenance and vigilance. ::Neil::

 

Welcome aboard Jigsaw!

 

Certainly not an easy one to call! I commend Mackburner on his very impressive and thorough report. However, as you have excepted this open to discussion, there are still niggling doubts in my mind just what happened and I'm wondering if you feel the same.
I feel that your conclusions are spot on but was wondering whether the 'shear' failure of the base plate could have been down to the lead solder reaching its melting point rather than shearing under increased pressure? we will never no for sure of course but the circumstances around the failure are not black and white. I hope you don't mind my comment.
Martin

 

Hi Martin,

I think that if the solder started to melt then you would have seen a "gentle" release of fuel and pressure. The dramatic state of the base plate, bent in that way, let me imagine a huge force acting against it and so only a great pressure could have done that sort of damage.

Anyway I guess that probably the solder started to reduce its strength because the extra heat and that for sure contributed to the later explosion.

Nicola

 

Well yes the solder may have been weakened by the heat but you can see in the image that this was not a gradual failure but sudden and catastrophic. So there can be little doubt it was a shear failure of the base plate seam. That can only have been from a very high pressure in the tank. Just heating the air above the fuel would probably not have achieved such a high pressure so I still believe the kerosene boiled and that would have induced a sudden rapid pressure increase. With no safety release an explosion or failure was inevitable. Boil any liquid in a confined space and when the liquid reaches vapourisation point the liquid flashes into gas. This is the power that moves steam trains weighing hundreds of tons and is not to be taken lightly. ::Neil::

 

All makes sense. But being pedantic, would the kerosene have boiled (materially) whilst it was in the confined space? It's like a pressure cooker - and the increased pressure from expansion and some vaporization would have raised the boiling point.

Once the same had split, the kerosene would have boiled rapidly, assuming it was above the necessary temperature for vapourisation at atmospheric pressure.

 

Maybe but the lesson to be learnt is if you heat a lamp tank enough it will go bang. Actually a pretty rare occurance. I only know of two Petromax clones erupting but they were running on gasoline and a small leak got seriously interesing very quickly and I did hear of a Tilley lantern attempting low earth orbit on a beach many years ago. So 4 in around 50 years is not a big problem. ::Neil::

 

...unless you happened to have been next to one of those four failures, clearly!

But it does go to show that nothing can be taken for granted and all lamps and lanterns need to be treated with respect. Keep them in tip-top condition by inspecting them before and after use, regular servicing and maintenance based on frequency of use, use the correct replacement parts when they're needed, follow the manufacturers instructions, don't cut any corners, keep an eye on them whilst in use and have a plan for when something goes amiss. Works for me (well, most of the time, anyway - I have been known to have the odd, er, 'emergency situation' from time to time...

 

BLEVE springs to mind

There are three characteristics of liquids which are relevant to the discussion of a BLEVE:[citation needed]

1. If a liquid in a sealed container is boiled, the pressure inside the container increases. As the liquid changes to a gas it expands - this expansion in a vented container would cause the gas and liquid to take up more space. In a sealed container the gas and liquid are not able to take up more space and so the pressure rises. Pressurized vessels containing liquids can reach an equilibrium where the liquid stops boiling and the pressure stops rising. This occurs when no more heat is being added to the system (either because it has reached ambient temperature or has had a heat source removed).
2. The boiling temperature of a liquid is dependent on pressure - high pressures will yield high boiling temperatures, and low pressures will yield low boiling temperatures. A common simple experiment is to place a cup of water in a vacuum chamber, and then reduce the pressure in the chamber until the water boils. By reducing the pressure the water will boil even at room temperature. This works both ways - if the pressure is increased beyond normal atmospheric pressures, the boiling of hot water could be suppressed far beyond normal temperatures. The cooling system of a modern internal combustion engine is a real-world example.
3. When a liquid boils it turns into a gas. The resulting gas takes up far more space than the liquid did.

Typically, a BLEVE starts with a container of liquid which is held above its normal, atmospheric-pressure boiling temperature. Many substances normally stored as liquids, such as CO2, propane, and other similar industrial gases have boiling temperatures, at atmospheric pressure, far below room temperature. In the case of water, a BLEVE could occur if a pressurized chamber of water is heated far beyond the standard 100 °C (212 °F). That container, because the boiling water pressurizes it, is capable of holding liquid water at very high temperatures.

If the pressurized vessel, containing liquid at high temperature (which may be room temperature, depending on the substance) ruptures, the pressure which prevents the liquid from boiling is lost. If the rupture is catastrophic, where the vessel is immediately incapable of holding any pressure at all, then there suddenly exists a large mass of liquid which is at very high temperature and very low pressure. This causes a portion of the liquid to "instantaneously" boil, which in turn causes an extremely rapid expansion. Depending on temperatures, pressures and the substance involved, that expansion may be so rapid that it can be classified as an explosion, fully capable of inflicting severe damage on its surroundings.

 

Remind me, please, what BLEVE stands for and how it's pronounced. I'm given to understand it's some sort of Americanism...