Aeroplane Hangar Ventilation

[mechanicaldup]

Hi

wehere can I find guidelines on the design of ventilation system on aeroplane hangars, (how to maintane the hangar under positive pressure etc...)?

 

[tombmech]

The NFPA Codes dictate hangar systems. In my experience, if there's any likelihood of fueled aircraft in the hangar, you would never want positive pressure. There are other restrictions as well - deluge systems/AFFF fire protection, and electrical equipment above 18" A.F.F.

 

[mechanicaldup]

Thks

The positive pressure is to prevent the ingress of dust..

 

[stanlsimon]

Take a look at NEC article 513. From the way you spell airplane maybe you are in the mother country, maybe this code wouldn't be binding, but it will help keep you from blowing up.

 

[mechanicaldup]

is the positive pressure creating a fire hazrd or what? I don't understand your reasoning

 

[tombmech]

Positive pressure prevents the displacement of stray vapors. Vapor concentration will continue to accumulate until an explosive atmosphere develops - with disastrous results.

Negative pressure ventilation (reads E-X-H-A-U-S-T) is fundamental for contaminant dilution. That is true regardless of whether you are designing an aircraft hangar, an automobile garage, a chemical/biological laboratory, or a food kitchen.

It is true that positive pressure is best for preventing the introduction of external contaminants. However, in the case of potentially fueled aircraft (even recently de-fueled ones) your HVAC'd item is the contaminant source.

Failure to address this properly can be lethal.

 

[walkes]

mechanicaldup,

You require the space to be negative but you can control the make-up air through a filtered make-up unit to reduce the possibility of dust contamination.

 

[mechanicaldup]

how many air changes is required to prevent dust ingress?

 

[tombmech]

In my experience, about the best you can hope for in an aircraft hangar is something the USAF defines as a "Controlled Area", or a "Class 300,000 Clean Room". Those standards include the following:

* 300,000 0.5 Micron particle count,
* 80 deg. F., 50% RH max,
* 2-stage filtration: 50-60% rough filter followed by 80-85% final filter, and
* minimum 10 air changes per hour.

They also include positive pressure in that list, but as noted, that should be an exception. This comes from USAF "T.O. 00-25-203, Contamination Control of Aerospace Facilities, U.S. Air Force", which was revised 3/85. My copy is most certainly out of date, but I doubt that the particular items we're discussing have changed that much.

Obviously, "Clean Room" as we normally think of it (such as in laboratories and semi-conductor production) involves drastically more complicated measures.