Patent ID: 8167848

Claim:
A safety syringe of the type for use with a hypodermic needle in which, following use of the syringe to inject medicament from its barrel, the needle is detached from the distal end of the syringe and retracted within the barrel of the syringe, thereby preventing accidental stabbing after use, comprising a. a plunger axially movable within the barrel and having therewithin a retraction lumen open at its distal end to receive the needle after use of the syringe; b. a gas release cell located within the assembled syringe distally of the plunger, intact and inoperative prior to substantial completion of injection of medicament by downstream motion of the plunger; c. gas release trigger means located within the assembled syringe distally of the plunger, and operable in response to downstream motion of the plunger as it approaches its downstream limit of travel to cause the gas release cell to release gas into the interior of the syringe; and d. a needle carrier for engaging the needle in the vicinity of its proximal end and carrying the needle into the lumen during retraction of the needle, the needle carrier having a distal bearing surface against which gas under pressure may bear, and movable into the plunger lumen under gas pressure so as to retract the needle into the lumen; wherein e. the lumen is dimensioned to receive sufficient of the combined length of the needle and the needle carrier that, after retraction, the needle is entirely within the syringe, and the needle thereafter remains in retracted position.