Waste Water Screening Room - NFPA -820 - ventilation/pressurization
Waste Water Screening Room - NFPA -820 - ventilation/pressurization
(OP)
I am looking at a screening room for waste water. NFPA-820 calls for <12 air changes per hour. As a math nerd, that reads to me as less-than 12 ACH, but I think it is supposed to be greater-than. It is a Class 1 Division 1 area. So I am supposed to have at least 12 air changes per hour in the room.
The NFPA-20 also says that this room needs to be -0.1"WC relative to ambient. That is a substantial negative to maintain in addition to a 12 ACH ventilation rate. The room is roughly 18,000 cubic feet, so 12 ACH is roughly 3,600 CFM. But now how can a -0.1" WC be achieved on top of that? The exhaust will need to be substantially higher than the supply.
In a truly sealed environment this could probably be easily calculated. It could also be done with some idea of the envelop cracks. In the case of this room, however, there is a channel of water under the "floor", which is steel grating. the channel comes from a combination storm/sanitary sewer, and goes to an underground holding tank that is surely vented. How can any kind of negative be pulled in a building with the gaping openings of a channel running underneath it?
I don't see how both criteria of 12 ACH and -0.1"WC can be achieved. Anyone ever run into something like this?
The NFPA-20 also says that this room needs to be -0.1"WC relative to ambient. That is a substantial negative to maintain in addition to a 12 ACH ventilation rate. The room is roughly 18,000 cubic feet, so 12 ACH is roughly 3,600 CFM. But now how can a -0.1" WC be achieved on top of that? The exhaust will need to be substantially higher than the supply.
In a truly sealed environment this could probably be easily calculated. It could also be done with some idea of the envelop cracks. In the case of this room, however, there is a channel of water under the "floor", which is steel grating. the channel comes from a combination storm/sanitary sewer, and goes to an underground holding tank that is surely vented. How can any kind of negative be pulled in a building with the gaping openings of a channel running underneath it?
I don't see how both criteria of 12 ACH and -0.1"WC can be achieved. Anyone ever run into something like this?
RE: Waste Water Screening Room - NFPA -820 - ventilation/pressurization
Another aspect that you should be aware is that the room volume that will be require in the D.E. does not necessarily mean the entire room since the air flow could be stratified and consequently the room volume could be taken within the breathing zone so for safe keeping up to 10ft. high if there is no elevated work zone.
RE: Waste Water Screening Room - NFPA -820 - ventilation/pressurization
The latest edition of NPFA states "Continuously ventilated at 12 air changes per hour" for Class I, Div. 2 applications such as you are decribing. Class 1 Division 1 is no ventilation or ventilated at less than 12 air changes per hour.
The -0.1"WC is a measure of how tight (in terms of building air leakage) the building is. You can't meet this standard with building doors open.
http://c.ymcdn.com/sites/www.ncsafewater.org/resou...
Regarding: "How can any kind of negative be pulled in a building with the gaping openings of a channel running underneath it?"
Come on man, be a little creative. You can furnish a water seal where the water must flow under a baffle wall to seal.
Some applications supply sealing covers over the channels.
Regarding: "Another aspect that you should be aware is that the room volume that will be require in the D.E. does not necessarily mean the entire room since the air flow could be stratified and consequently the room volume could be taken within the breathing zone so for safe keeping up to 10ft. high if there is no elevated work zone."
This is an incorrect statement and not included in NFPA 820.
RE: Waste Water Screening Room - NFPA -820 - ventilation/pressurization
RE: Waste Water Screening Room - NFPA -820 - ventilation/pressurization
RE: Waste Water Screening Room - NFPA -820 - ventilation/pressurization
GG
"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)
RE: Waste Water Screening Room - NFPA -820 - ventilation/pressurization