Artistic licence

Like all those 1900-1980 period dramas where no-one smokes

The only purpose of the fuel gas when cutting is to get the metal cherry red. Once at temperature the cutting process does not need a fuel gas, as the reaction between hot iron and oxygen is exothermic. Once started the cutting process is self-sustaining. So oxy-propane is fine for cutting, and is widely used commercially as propane is cheaper and easier to handle than acetylene.

Andrew

Correct except the flame produced by a Thermic Lance is hotter than Oxy-Acetylene! The volume of heat produced by a lance is typically higher too unless the Oxy-Acetylene torch is massive.

Oxy-Acetylene 3000 to 3480°C, Thermic Lance 2730 to 4500°C

The lance consists of a steel tube, several feet long and packed with fine steel wire and some flux. Oxygen is fed in one end and the other ignited with a flame hotter than 1600°C : usually Oxy-Acetylene or Oxy-Propane.

The burning steel produces a puddle of molten Iron Oxides hotter than the melting point of steel, which serves to concentrate and promote heat flow into the target whilst directing hot Oxygen into it. Run flat out and Oxygen rich, the flame is well above the boiling point of steel, and the vapour also ignites adding even more energy to the burn.

Although Thermic Lances easily cut Concrete, Steel and pretty much everything else, they're not precision tools! Used to break into a safe or vault, there's a high-risk the contents will be destroyed by the huge amount of heat.

Anyone know what the hottest possible chemical flame temperature is?

I think Hydrogen and Fluorine burn hotter than 4500°C but high temperature facts are hard to come by. Another possibility is Fluorine Tetrachloride, which I remember fondly because Asbestos burns in it!

Dave

Edited By SillyOldDuffer on 29/10/2022 14:52:20

A misunderstanding. I digressed into hot burning substances out of interest rather than meaning to suggest they were practically useful for safe breaking! Far too dangerous and – like a Thermic Lance – all too likely to destroy whatever is in the safe.

The film industry is good at spectacle and tends to slide over mere details. For example, a Thermic Lance produces a lot of heat and smoke, so bad in a confined space like a tunnel something elaborate would have to be done to protect the crooks whilst not calling attention to the robbery.

Another method that doesn't work in practice is to bore a hole in the roof, fill the vault with water, and then freeze it. The force exerted when water expands as it freezes is sufficient to burst safes, but the process also soaks and crushes the contents. And before the master criminal can escape with the loot he has to melt a large quantity of ice – not easy to do quickly!

I enjoyed 'Sewers of Gold' though. Anyone know if Albert Spaggiari used a thermic lance in the real robbery? He definitely welded the vault doors shut from the inside to delay discovery.

Dave

Hi, as Andrew Johnston has said, oxy-propane is often in industry for cutting iron/steel, and more often in scrap yards, as propane is cheaper, and you don't need to get the metal up to melting point, but you do need a different cutting nozzle, which is a two part one, the inner part being made of brass, and an outer shield made of copper. A thermic lance doesn't need a fuel gas supply, it just needs the end heating up with any type of flame capable to get it up to a cherry red, even a blacksmith's forge will do, and then the oxygen is turned on once it's hot and the reaction will keep going, the lance being a consumable.

Regards Nick.

Edited By Nicholas Farr on 31/10/2022 07:56:23

At least they got the bike right that time!

Unlike Steve McQueen in "The Great Escape" in the famous jump over the fence scene. The supposedly stolen German military WW2 BMW was obviously a 1961 Triumph TR6. It would have been more spectacular on a 1944 BMW I am sure!

Robert de Niro used a variant of this idea in The Score; having filled the safe with water from the sprinkler system he lowered an explosive charge into it – his explanation "it's just physics".

I shall look out for Golden Sewers.