Arsine poisoning.

Nature of the Accident Tin is manufactured on a very large scale in Bootle. It occurs naturally as pyrites, and arsenic is an invariable contaminant. The chemical composition of the ores varies considerably but arsenic is present in a concentration of up to 3 %. The tin is liberated from its ores by heating with carbon. The arsenical impurities float to the surface of the molten tin and form a dross which has a high arsenical content. The dross is skimmed off and heated in another furnace in order to oxidize all the arsenic and in this form it is free of hazard. The tin is further purified by adding to it aluminium in the form of an aluminium-tin alloy. This causes the formation of aluminium arsenide, which has a higher melting point than that of tin and therefore floats to the surface as dross. It is a well recognized hazard of the tin smelting industry that this aluminium arsenide, when it comes into contact with water, generates arsine or arseniuretted hydrogen, which is highly toxic. Material which may contain aluminium arsenide is not, therefore, left lying about the factory. On the day of the accident, a small amount of the dross from the aluminium-tin alloy melting was mixed with the roasted dross from the smelting furnace; the latter is known to be free from arsenide and the former is now known to contain it. This mixture was accidentally moistened. On this particular occasion, two men, J. E. and S. J., had been shovelling the dross mixture. A third man, A. B., was employed in bringing this dross by truck from another part of the factory. In error, he loaded also into the same truck some moist material which consisted of gutter cleanings put there by men who were repairing the roof. Thus, in the truck were mixed three substances: roasted arsenical dross from the smelting furnace, which is safe, dross from the alloy furnace, which had become contaminated with arsenic, and waste material containing moisture. This mixture generated arsine which caused the accident. When the men were taken ill the Works Manager immediately suspected arsine poisoning, because a similar accident had occurred at this factory 21 years previously. He immediately sent the severely affected men into hospital, and instructed other workmen to attend hospital if they felt ill. He then caused the affected area to be cleared, and had bleaching powder spread over all suspected material to oxidize arsenical compounds.