Vessels not freed from hazardous material

In these incidents the vessels were correctly isolated but were not freed from hazardous materials. 

If a part of the vessel cannot be inspected and be seen to be safe, then we should assume the vessel contains hazardous materials. 

Tf the previous eontents were flammable, we should assume there is some flammable material out of sight. 

Gas tests alone are not eonclusive. There may be some sludge present that gives off gas when heated or disturbed. 

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