FOUR major changes occur when a large number of people occupy a confined unventilated space. Two of these are obvious by its collective breathing, the crowd reduces the oxygen content of the air, and increases the proportion of carbon dioxide it contains. In addition, body heat from the assembled humans increases the temperature of the surroundings, and the moisture of their exhalations brings about a rise in the humidity. The combination, taken to extremes, may well be lethal, as can be gleaned from two notorious examples in the history books.
The most infamous is that of the Black Hole of Calcutta, a phrase which recalls an event which took place in British India in June, 1756. As a contemporary account described it: "On one of the hottest of the hot nights of that year, Sarij Uddaula, a youthful, merciless ruler of Bengal, caused to be confined within a small cell at Fort William 146 Englishmen whom he had that day captured in a siege of the city of Calcutta. The room was large enough to house comfortably but two persons. Its heavy door was bolted; its walls were pierced by two windows barred with iron through which little air could enter.
As the steaming mass of human bodies vied for the insufficient air, breathing became difficult, and there were vain onslaughts on the windows and attempts to force the door. The night passed slowly, and with the advent of morning death had come to all but a score of the luckless company. This tragedy will forever remain as the most drastic demonstration in human history of the bondage of man to the air by which he is surrounded."
The post famine years in Ireland, however, provided an example equally tragic and of similar proportions. In late November, 1848, the paddle steamer Londonderry left Sligo, bound for Liverpool, with a large number of emigrating passengers accommodated in the hold. As it passed along the coast of Donegal a violent storm blew up, and grills on the deck of the steamer, which effectively acted as ventilators for the hold, were blown off by the gale. To prevent water entering the holds, the crew covered the openings with tarpaulin.
On December 1st, 1848, the Londonderry took shelter in the port from which it took its name. When the covers were removed, it was found that 72 men, women and children had perished, victims of the same fate that befell the captured soldiers in Calcutta nearly a century before. They were buried together in a mass grave near Derry's workhouse in the Waterside area of the city.