Question

There is a chemistry laboratory. You are called in as an emergency consultant. A container of 1 kilogram of liquid benzene broke and spilled its contents onto the floor. The room is 40 feet x 30 feet and 8 feet high. There was a graduate student in the laboratory breathing for an hour after the breakage occurred (without noticing it). Then the room was evacuated.After the evacuation, the liquid is totally removed, and the room ventilation continues to be maintained. How long would you recommend that the room be unoccupied until it can be regarded as “safe”. the air flow rate of room is 3m/s

Answer 1

The liquid benzene evaporates at a rate: 5g/min (say) then it spreads in the room of volume 40*30*8 ft^3 or 271.842 m^3.
Now, let's say the dimension of air blower is 0.5m*0.5m = 0.25m^2.

Also, the air wouldn't mix completely in room, So let's consider a mixing factor of 10.
Then the time taken to remove benzene vapors is : (volume of room) / (inlet air rate/10)
= ((271.842) / (0.25/10) (m3 / (m3*sec))
= 10873.68 sec = ~181.23 min = ~ 3.02 hrs

So to remove benzene vapours it will take approximately 3.02hrs for a 0.5*0.5 m^2 air ventilator.