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Tunnel restrictions for LPG
Page 82
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WWe refer to your article by Johnny Johnson entitled "Road tunnel LPG restriction will be expensive" (CM August 9).
We would like to congratulate you on a good article which certainly brings out the very real disadvantage of the proposed tunnel restriction being enforced. Nevertheless, we would bring to your attention several points in the article on the safety aspects of LPG.
Leakage of LPG in a tunnel would certainly not mean that "an explosion is inevitable. A considerable amount of gas would have to be released before any hazard is present, It is worth remembering that a mixture of 1.4 per cent of petrol vapour in air is inflammable whereas 2 per cent mixture in air of LPG is required before an inflammable state is reached.
You mention that storage tanks should be constructed to a specification; we would like to point out that these LPG storage tanks are constructed to the Home Office Gas Container and Cylinder Committee recommendations. The tanks are mounted midships in the vehicle thereby avoiding the large majority of accidents. They are designed to withstand an impact and in the unlikely event of the tank being severed from the connecting pipe a purpose-built excess flow valve, manufactured into the tank design, will prevent excessive loss of gas to the atmosphere.
Notwithstanding the above, if a large quantity of gas were present in a tunnel and found a source of ignition, then a flash would most likely be caused not an actual explosion (it should be noted that the ignition temperature of petrol is 500°F and LPG 1000°F). What could cause an explosion is the LPG tank, but all these are fitted with pressure relief valves that are designed such that any build-up of pressure generated by external means of heat would be released through the pressure relief valve, therefore not allowing the tank to explode.
Referring now to the connections and fittings on the vehicle: they are, of course, mainly either brass or steel and any leakage from the connections would certainly not be sufficient to cause a fire of any size. Naturally, the tank excess flow valves still come into operation if a large leak occurs on the installation connections or fittings.
The carburation equipment used on the engine varies slightly in design according to manufacturer, but all regulators/demand valves have to be designed such that they will only pass gas when the engine is in operation.
We trust this letter will bring to your readers notice the large amount of consideration that is given by the LPG industry to the safety aspects of LPG when used in the road transport industry. This is further borne out by our 100 per cent safety record in this field.
If we can be of any assistance to you in your efforts to combat these restrictions we would be delighted to help. P. J. GREGORY, Sales Executive, Ca/or Gas Ltd, Slough.
[Johnny Johnson comments: "That an explosion would be inevitable when LPG was leaked in a tunnel was stated eta meeting called by the GLC in 1971, and this view was supported by nearly everybody to whom I spoke when preparing the article. The tanks may be constructed, in the main, to Home Office committee recommendations but these are not mandatory. One large refrigerated fleet operator told me that many connections (though not in his fleet) were simple rubber hose." — Ed.]