If you (or any other witness) know first aid, you might consider applying it to any casualties before the emergency services arrive. Remember the ABC rule - Airways, Breathing and Circulation. Limit bleeding by applying force to the wound and raising up the injured part as much as is possible. If you suspect there are broken bones, don't even consider to move the casualty. Cover them in a blanket until the emergency services arrive. They need to keep warm, particularly as they're likely to be shocked. With burns, pour cold water over it for twenty minutes or until the pain subsides.
