The average length of the car parking spaces is an absolutely vital parameter the parking ventilation designer pays attention to. The space is naturally determined by the overall size of the construction, as well as traffic management schemes and the number of cars, standing at a certain time in a queue to enter or exit the parking lot. According to the United Kingdom statistics, such movement duration typically equals from 60 to 600 seconds. On average, however, it can be assumed that these values are in the range of 60 to 180 seconds. Thus the average duration of entering equals 40 seconds approximate, while it takes around 55 seconds for the vehicle to leave the carport. It should be borne in mind that the parameters of the engines of the cars in the garage and in normal traffic differ significantly.
The entering vehicles enter the lot with the motor warmed up, reducing their speed to 5-8 km/h Therefore, their ‘contribution’ to the pollution of the environment is limited. However, the leaving cars, on the contrary, emit more exhaust gases due to their cold engines in low gear. It should be noted that the level of emissions is significantly higher in winter than in summer, since the engines are colder the winter; these numbers can be almost five times higher. Thus, e.g. U.S. Board of Industrial Hygiene recommends the maximum permissible value of the concentration of CO at the level of 29 mg/m3 for a period of not more than 8 hours. In turn, the Environmental Protection Agency (EPA) states that for territories at sea level or close to it, the concentration of 40 mg/m3 of not more than an hour is not harmful to health. Conversely, more stringent standards are set for the altitudes of 1,000 meters and above. Thus, erecting a fully-compliant parking lot demands installing a car park ventilation system adjusted thoroughly to the parameters mentioned above.