Posted By Mitch Forced ventillation will always take the path of least resistance, therefore if a door is opened in the room/chamber this would normally offer less resistance than a ducting system, especially an acoustically treated system.

Posted By Frank Newman May, I'm really not sure what you mean by "high risk" High risk to employees is one thing, high risk to end-users is something else. However, assuming that you are more likely to be talking about a clean environment which ensures that cleaned clothes do not contaminate their in-use environment then your engineer is a total pillock. Clean rooms, operating theatres, lab hoods need an assured unidirectional air-flow. The air will be designed to flow in, across contaminated areas and out (though filters if necessary) in a direction that takes it away from employees and nominally clean/sterile materials. Opening doors and windows may make employees feel more comfortable but will do nothing to ensure the non contamination of the materials you are responsible for. Get the air conditioning fixed, your engineer fired or replaced and check the air flows. I have found that speed (metres/second or feet per minute) is, in similar circumstances, more important than volume or changes-per-hour. Changes per hour is OK for employee well being. Air speed is more important where contaminants are concerned. Make-up air is also necessary. This could come from an open door, so long as it flows directly to the extraction point. But normally it should be designed into the system : example : for a laboratory hood make-up air comes from the front edge of the hood, flows across the material being handled and is removed by extraction horizontally across from the handler. Not by an overhead "chimney" Merv

Posted By May Warley Thanks alot everybody. I am currently in a difficult position as my boss wants me to ensure that all doors are shut but I hv worked in that environment before I got this job and it wasn't pleasant at all. May

Posted By steve e ashton John: Your advice about negative pressure is correct when you want to keep something in. But is wrong when you want to keep something out. So for high risk work on bacteria etc, negative pressure, with filter on the extract. For kitchens, operating theatres etc - positive pressure, filter on the inlet. Steve

Posted By Frank Newman I think, from looking at the original question posed by May, that the risk is for the quality/sterility of the product. The A/C broke down a few months ago. Employees are concerned about their working conditions. Site pillock is insisting that rules be respected even though situation has changed (A/C which requires doors to be kept closed to respect airflow requirements even though A/C is no longer working) The site pillock is a pillock and should spend more time on getting the A/C fixed than on insisting that employees work in unsuitable conditions. That way he/she/it could better protect the company from loss of business or a possible law suit. Has he/she/it got a quote for fixing the A/C ? Merv