German law sorts fireworks into four categories by the danger they pose. Category F1 poses a very low danger and is meant for use indoors. It may be sold to people aged 12 and older. Category F2 poses a low danger and is meant for limited outdoor areas. It may be handed only to adults, and shops may sell it to the public only from 29 to 31 December. Adults may set it off without a permit only on 31 December and 1 January. Only staff aged 18 or older who have been instructed may sell fireworks. Category F3 poses a medium danger. Category F4 poses a high danger and is meant only for people with expert knowledge. Both may be set off only by holders of a permit or a Befähigungsschein, a certificate of competence. For F4, the minimum age is 21.