From the Industrial Ventilation Handbooks,  there are formulas for dilution ventilation for fire and explosion. I do not have air samples to determine concentrations,so I was trying to determine an evaporation rate for cyclopentane

hugofelix

If this thread is in regard to a spill of cyclopentane forming a pool of some dimensions and the amount of air exchanges needed to prevent a flammable or explosive atmosphere, some information on the evaporation rate can be found but real rates at particular conditions have to be estimated by modeling of mass transfer.
Evaporation rate are often expressed as ratio's relative to the evaporation of butyl acetate.  Actual rates (mass/area/time) are available on a limited basis.  The rate for a particular chemical spill depends upon the liquid temperature, the air temperature, atmospheric pressure, humidity and air flow.
Cyclopentane has a flash point of 19 F.  It's evaporation rate is 10 relative to butyl acetate.  A literature value for a pure cyclopentane spill at an air temperature of 300 K, an atmospheric pressure of 101.3 KPa, and an air velocity of 0.17 m/s is 0.68 mmol/square meter/second.  There is a literature article that looks at this subject.
http://annhyg.oxfordjournals.org/cgi/reprint/45/6/437
This info may not be what you are looking for.
Bill Choate