If somebody has crashed really hard and is unconscious, don't try to remove the helmet. Check to see if they are breathing and what their pulse is. Make sure their airway is clear(tongue not bleeding, broken teeth not lodged in the throat. Keep their feet elevated to keep blood to the head. A spare tube can be used as a sling or a tourniquet(so long as you know where to apply it). Patches and patch glue can be used to stop/slow a bleeding cut.
If someone has hit their head but is conscious, have them stay lying on the ground and still for several minutes to make sure they don't go into shock.
Most states have good Samaritan laws that allow you to give help without fear of a lawsuit so long as you are doing what is within your training.
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