Ok, you are the first responder to an accident, car wreck and there is a SPURTING ARTERY from an arm or leg or something....
What do you do first?
First, check your own pulse.... that is the joke in medical school. But really: safety first. If something is about to blow up or burn, move yourself and the victim. Call 911 or yell at someone else to... send someone to flag other cars to slow down so you don't have more cars piling into the mess....
Airway: if the person does not have an airway, you can apply tourniquets to all four limbs and you will still lose the victim. Check and clear it.
Breathing: Are they breathing?
Circulation: Well, if there is a spurting artery, this is covered. There is definitely a heartbeat.
NOW stop the bleeding....
Have an emergency blanket, a towel, an ace wrap, a cheap CPR mask and gloves in your car. You can use a towel and ace wrap to splint or put pressure on bleeding. Try to keep the victim from going into shock: elevate their legs if you can. If you can't or they are tangled up in a vehicle or you aren't sure about their neck, just try to keep them a little warmer. Use that emergency blanket.
RedOmega adds that if someone has been knifed, don't pull it out. Let the hospital to it.