Chemicals are stored in a laboratory with volume V (m³) As a consequence of poor laboratory practices a hazardous species, A. enters the room air (from inside the room) at a constant rate m_A (g A/h). The room is ventilated with clean air flowing at a constant rate V _air (m³/h). The average concentration of A in the room air builds up until it reaches a steady-state value C^A.r (g Aim³).

(a) List at least four situations that could lead to A getting into the room air.

(b) Assume that the A is perfectly mixed with the room air and derive the formula mA = V _air C_A

(c) The assumption of perfect mixing is never justified when the enclosed space is a room (as opposed to, say, a stirred reactor). In practice, the concentration of A varies from one point in the room to another: it is relatively high near the point where A enters the room air and relatively low in regions far from that point, including the ventilator outlet duct. If we say that C _{A. duct} = kC_A, where k A = Kv _air C_A. Use this equation and the ideal gas equation of state to derive the following expression for the average mole fraction of A in the room air: where MA is the molecular weight of A.

(d) The permissible exposure level (PEL) for styrene (M = 104.14) defined by the U.S. Occupational Safety and Health Administration is 50 ppm (molar basis). An open storage tank in a polymerization laboratory contains styrene. The evaporation rate from this tank is estimated to be 9.0 g/h. Room temperature is 20?C. Assuming that the laboratory air is reasonably well mixed (so that k = 0.5), calculate the minimum ventilation rate (m3fh) required to keep the average styrene concentration at or below the PEL. Then give several reasons why working in the laboratory might still be hazardous if the calculated minimum ventilation rate is used.

(e) Would the hazard level in the situation described in part (d) increase or decrease if the temperature in the room were to increase (Increase, decrease no way to tell.) Explain your answer, citing at least two temperature effects in your explanation.

YA MA RT kVair MAP