| Summary: | The mercury flame failure device (F.F.D.) has now been in existence for approximately 30 years and in the United States, Canada and Britain there is now estimated to be a field population of 42,000,000 of these controls, with a current production rate of 2,350,000 units per year. Recently several problems have been identified which threaten the future of the mercury F.F.D., notably the toxicity of the mercury fill, and the relatively short life of the devices under some operating conditions. This work examines the background to the mercury F.F.D. and the problems associated with it. A new type of F.F.D. was developed, for which patents have been applied. This device was filled with an inert gas, and was found to have all of the advantages of the mercury F.F.D., without the problems associated with the mercury. Prototypes were constructed which had sufficient performance and reliability to substitute for the mercury F.F.D. Computer programs were developed to enable performance predictions to be made for gas filled devices and design data is given to enable the optimum design parameters to be selected for a particular application. The reliability problems associated with the new device were investigated and suggestions are made to enable maximum reliability to be achieved. Finally the marketing of the new F.F.D. was studied. The existing market for the mercury F.F.D. was examined and the chances of the new F.F.D. succeeding in this market were considered. It was found that, given competent development, production and enthusiastic marketing, there were no reasons why the new F.F.D. should not succeed in the market place.
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