A method for retaining aerosols when accessing a sealed vial is disclosed. The method includes the steps of piercing the vial seal with a sharp cannula having a medicament lumen and a vent lumen, introducing a liquid through the medicament lumen into the vial, and conducting gas out of the vial through the vent lumen and a vent port to the atmosphere. The method also includes the steps of blocking the passage of non-dispersed liquid out the vent lumen at a first filter device comprising pores having a diameter in the range of 0.2-3.0 microns, absorbing liquid dispersed in gas at a second filter device, and inhibiting the passage of bacteria at a third filter device having a pore size smaller than 0.2 microns.
