Maintaining the proper differential pressure in laboratory spaces is one of the most challenging tasks facing the laboratory environmental control engineer. Some of the items which need to be addressed when designin a space pressurization control system are:

•  Hazard Assessment
• Constant volume vs VAV systems
• Differential pressure vs differential volume systems
• Negative vs positive pressure requirements
• Controls signal to noise ratio
• Control stability and sped responses
• Failure mode analysis
• Building construction impact on space pressure control
• Duct leakage impact on space pressure control

Laboratories and clean room s may require that a differential pressure be maintained between them and the adjoining spaces. this requirement may come from code considerations or  from the operation requirement of the space. for example, NFPA-45 states that "laboratory work units and laboratory work areas in whuich hazardous chelmicals are beings used shall be maintained at an air pressure that uiis negative relative to the corridors or adhacent non-lbaortary areas. This is to prevent the migration of fire, smoke and chemical releases from laboratory space. Labs containing radiation hazaqrds or biohazards may also be required by diuifferent agencies to maintain a negative pressure to contain these hazards. Clean rooms, on the other hand, are nomrally operated at a positive static pressure to prevent infiltration of particulates. Even if yours buildings codes and regulatory agencies do not require pressurixation you may wish to include this feature in your facility anyway for the reasons decribed above.