Lab Exhaust Fan Shutdown

[WoodrowJWeen]

Is there any code that requires that laboratory exhaust systems be shut down by the building fire alarm system in the event of fire. These would include lab hood exhaust, biosafety cabinet exhaust and general lab exhaust. Seems to me that you would want these fans to be on during a fire to ensure that the bad "stuff" being exhausted doesn't get involved in the fire and make the smoke situation worse.

 

[imok2]

The requirements for this would probably be found in NFPA 45

 

[lilliput1]

They fall under Hazardous Exhaust System, Section 510 in the 2003 International Mechanical Code. They do not need fire damper however they are required to be contained in dedicated fire rated shafts. Risers are not allowed to combine exhaust from different floor levels. Instead separate risers from each floor are required. They may be combined in a dedicated shaft. Other air systems are not allowed to share shafts for hazardous exhaust. Provide spare space in shaft for future addition of addition fume hood exhaust.

 

[WoodrowJWeen]

Thanks imok2, per NFPA 45 fans shall NOT shut down.

 

[gatoruf]

This just came up on a job of ours. We were aware of the NFPA requirement, but had over 20 - 6 foot hoods. You couldn't open the doors to exit the building with the make-up air AHU's off and the lab fans on. Our were on VFD's so we revised the sequence to slow down the fans in the fire alarm mode until we could meet the 15 lb maximum door opening requirement. Also if you're trying to comply with ANSI Z9.5 the fans need to be on emergency power.

 

[lilliput1]

Gatoruf,

Slowing down the fans would not be enough. You would also need to reset the air valves accordingly to reduce the exhaust at each point. In addition to emergency power, there should be multiple exhaust fans (& supply fans) for reliability.
With dual fans, operation at one fan would reduce volume to approximately 60 to 70%. Thus at one fan operation w/ normal dual fans, the air valves should be reset to a setback position that would approximately maintain the design pressurization & without exceeding the 15 lb limit to open doors, and the capacity of the single fan.

If the air valves are not reset, control would not be maintained at the remote portions of the ductwork.

 

[gatoruf]

Lilliput,

Yes, air valve volumes were reset (or the remote valves would draw little air with the closer valves wide open), and there are multiple fans (3 at one location, four at the second - one in each group is redundant).

Originally we suggested partial fan shutdown, but the AHJ's intreprtation was the code requires all of the operating fans to remain on, so we just slowed them down. All the drives have a gateway to our EMS, and we were able to fine tune the speed to get just below the 15lb force.

Different ways to skin the cat!