This is only a guess based on what I know from my own experience. Detonators for demolition purposes could be transported in their inner containers within their brown outer containers such as the H84, in a large red-coloured outermost container. The outermost container was known as a "coffin" because of its size (large) and robust construction (thick steel with the lid firmly secured in place by bolts). This is clearly not a "coffin" but just a normal large ammunition container painted red. I wonder if, in the absence of a "coffin," it was used as a "coffin," but used that way it would be against transport regulations. The letter "B" may be an indication of the compatability group of the collective contents, which would be correct for detonators. "Various" might simply mean different models of detonator, e.g. L1, and L2, stored within the red outer container in their respective packaging. If the box was indeed used for transporting detonators then it would most likely be only for a local and temporary purpose.