A bar house with volume of 500 m^3, has 50 smokers in it. Each begins to smoke 2 cigarettes per hour at time t=0 hr. An individual cigarette emits about 1.4 mg of formaldehyde (HCHO). Formaldehyde converts to carbon dioxide with a reaction rate coefficient k=0.4 /hr. No fresh enters the bar and no air exits the bar. Assume oxygen content is always sufficient (for human breath and cigarette combustion). The bar is a complete mixing environment with 1 atm of pressure at 25degrees C. If the threshold for people to feel eye irritation is 0.05 mg/m^3 of HCHO, how long will it take for people to feel that?