While evaluating impact of a toxic release, you may be interested in how the concentration of the toxicant increases in a room and its impact on indoor personnel. For example, if there is a H2S release in the plant and you want to estimate the increase in concentration in a nearby office building.

I want to share a simple model to estimate indoor concentrations following an outdoor toxic release.

Being a chemical engineer by background, the indoor dispersion represents an excellent opportunity to apply equation for well-mixed reactor.

In the above equation,

 – Indoor toxicant concentration at any time t

– Concentration of toxicant entering the indoor room (assumed constant in this model)

 – Air exchange rate (#exchanges per hour)

With the above model you can see how the concentration in an indoor room will increase with time. As time goes to infinity the indoor concentration will equal inlet concentration. If you want a spreadsheet cotaining the above equations, please email me with the subject line “indoor dispersion”.

Be careful while choosing the value for inlet toxicant concentrtion entering the room – remember your toxicant concentration should reflect any dilution that may have occured prior to entry.