a plunger is provided for a syringe that includes a pressure relief mechanism that exhausts any fluid trapped in the chamber between sealing flanges carried by the plunger when the plunger is advanced to dispense fluid from the syringe . the contact pressure between the barrel - contacting surface of the rearmost sealing flange nearest the access opening of the syringe barrel is weakened relative to the contact pressure provided by the barrel - contacting surface of the sealing flange that isolates the fluid within the barrel . the contact pressure of the rearmost sealing flange may be lessened by either reducing its radial diameter relative to the radial diameter of the other sealing flange , removing an underlying portion of the plunger , or configuring the rearmost sealing flange as deflectable sealing lip .