N = Q/V x 60 min/hr

Where:

Q= volumetric flow rate in cfm,

V = volume in cubic feet

N = air changes per hour (ACH) Note: in your lab this was referred to as RACH.

V = Qt

Where:

Q = volumetric flow rate in cfm

t = time in minutes

V = volume

Q = KG/C x 10⁶

Where:

K = mixing factor, unit-less (also referred to a safety factor)

G = Generation rate of contaminant in cfm

C = Concentration at standard (PEL,TLV or REL) in ppm

Q = Required volumetric flow rate in cfm

You will also need molar conversions.

How long does it take to change the air in a room twice? Given a room 39 ft x 28 x 9 ft and a ventilation rate of 2,457 CFM?