We have all experienced at least once the bad effects of overcrowding in a cinema, bar or in a theater. This happens due to physical factors as there is no evaporation of heat from the surface of skin. The prevention of heat loss by radiation causes heat stagnation and people suffer from drowsiness, headache, lassitude, nausea, vomiting which may lead to unconsciousness or death. In the past, it was believed that these symptoms were caused entirely by the changes in the air by respiration. However, it is proved that the increase of carbon dioxide and organic poisons from the expired air as well as the decrease of oxygen are not sufficient by themselves or even in combination to produce these symptoms unless other conditions, such as the stagnation of air, increased humidity and rise of temperature which are present in the overcrowded room.
Natural sources of ventilation are not possible, where a large number of people are congregated for a considerable long period and where climatic conditions do not permit free use of open doors and windows. Therefore, artificial ventilation is largely resorted to in these places and the mechanical means are used to facilitate the renewal of air.
The use of mechanical ventilation system has many advantages:
1. The incoming air can be delivered at any level and at any rate.
2. It can be warmed in cold weather by passing through heated pipes.
3. It can be cooled and humidified by passing through cold sprays of water.
4. Air can be filtered and made free from dust by passing through the filtering screens of wool.
Immediate effects of overcrowding in a room are the follows:
– Chemical changes – In mixed gathering of all age groups, the output of carbon dioxide is very high
–Physical changes– These includes :
(1) Rise in temperature – indoor temperature rises, as a result of the elimination of body heat
(2) Increase of humidity – Expired air contains about 6% water vapor due to moisture evaporated from skin and lungs. There is, therefore, an increase in the relative humidity;
(3) Decrease in air movement – Natural movement of air is impeded in crowded places.
(4) Body odors, bad breath, perspiration, dirty clothes, bad oral hygiene and other sources – give rise to bad odors in air.
(5) Bacterial population – organisms are discharged in the air during conversation, coughing and sneezing.
Unless vitiated air is replaced by fresh air, the effects of overcrowding may adversely influence the comfort, health and efficiency of the occupants. There may be feeling of suffocation, headache, drowsiness and inability to concentrate. There may also be droplet infection and lower resistance to disease. Because of all these side effects of contaminated air, artificial ventilation system must be included in every construction plan.