Closing the door on contamination

Mark A. DeSorbo

WASHINGTON, D.C. — Opening and closing the door to an autoclave or freeze-dryer could alter the temperature and airflow in a pharmaceutical cleanroom, creating a contamination risk.

Cleanroom engineers, however, can expect air to be about 10 percent cleaner under automated operation and as much as 20 percent better during manual operation by installing HEPA-filter units above autoclave and freeze-dryer door openings.

This discovery is the basis of Cantinka Ullmann's master thesis work, which was presented at the 1999 PDA annual meeting in late November. “The solution is to supply more clean air around the openings,” says the cleanroom engineer for Pharmacia & Upjohn (Stockholm, Sweden).

The amount of airflow, she says, depends on the difference in temperature between the autoclave or freeze-dryer chamber as well as the room and the size of the door opening. “Airflow over a door can arise from a difference in density caused by the difference in temperature, a pressure difference and the movements of the door and people,” Ullmann adds.

Click here to enlarge image

To determine how great the airflow should be from the HEPA-filter assembly, she conducted 16 airflow measurements on an autoclave and five on a freeze-dryer. She also used vapor to see air movements and noted temperature and air velocity in her research.

Ullmann then came up with a formula that factored the airflow discharge and velocity, the openings' width and height, and the density mean and difference. She recommends that more clean air should flow from the HEPA filter when operations are conducted by cleanroom personnel, while less air is needed if autoclaves and freeze-dryers are outfitted with robots.


Easily post a comment below using your Linkedin, Twitter, Google or Facebook account. Comments won't automatically be posted to your social media accounts unless you select to share.