Most modern vehicles have airbags and seat belt pre-tensioners which may need to be repaired or replaced over time. Many such devices incorporate a small explosive charge/pyrotechnic ignition device and should be treated with the appropriate level of care. If you store or work on such devices, you need to be aware of the risks involved and the precautions to take.
There is specific legislation covering the manufacture, sale/supply and storage of explosives (The Explosives Regulations 2014 and The Pyrotechnic Articles (Safety) Regulations 2010) which will apply in addition to other general health and safety legislation.
The amount of explosive that can be stored and where it must be kept depends on the type of explosive and the quantity. The Net Explosive Content (NEC) is an important detail you need to consider, since it will tell you the actual amount of explosive, ignoring the weight of other components and packaging which make up the article.