The
basic room purge equation is used in
industrial hygiene. It determines the time required to reduce a known vapor concentration existing in a closed space to a lower vapor concentration. The equation can only be applied when the purged volume of vapor or gas is replaced with "clean" air or gas. For example, the equation can be used to calculate the time required at a certain ventilation rate to reduce a high
carbon monoxide concentration in a room. D_t=\left [ \frac{V}{Q} \right ] \cdot \ln \left [ \frac{C_\text{initial}}{C_\text{ending}}\right ] Sometimes the equation is also written as: \ln \left [ \frac{C_\text{ending}}{C_\text{initial}}\right ] \quad = {-}\frac{Q}{V} \cdot (t_\text{ending} - t_\text{initial}) where t_\text{initial} = 0 •
Dt = time required; the unit of time used is the same as is used for
Q •
V = air or gas volume of the closed space or room in cubic feet, cubic metres or
litres •
Q = ventilation rate into or out of the room in
cubic feet per minute, cubic metres per hour or
litres per second •
Cinitial = initial concentration of a vapor inside the room measured in
ppm •
Cfinal = final reduced concentration of the vapor inside the room in ppm ==Dilution ventilation equation==