Hazop of tank trucks

Hazop has been applied mainly to fixed plants, but application of the technique to tank trucks used for carrying anhydrous ammonia and liquid carbon dioxide disclosed a number of hazards [11]. 

The tank trucks were not fitted with relief valves—normal European practice for toxic liquids. The study showed that the plant was designed for a higher pressure than the tank trucks and that in certain circumstances they could be overpressured. Modifications were made. 

Some of the older tank trucks were made from grades of steel that are brittle at low temperatures, and they are never moved at temperatures below 0°C. It was discovered that some customers wanted liquid carbon dioxide delivered at less than the usual pressure, and arrangements had to be made for them to be supplied only by selected tank trucks. (All new tank trucks are capable of withstanding the lowest temperatures that can be reached.) 

Some customers complained that there was oxygen in the ammonia. It was found that the road transport maintenance department was preparing tanks for repair by w ashing them out with water and then returning them 

Learning from Accidents, 2nd edition, Butterworth-Heinemann, Oxford, UK, 1994, Chapter 2. 

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