CONTRASTACIÓN DE LA HIPÓTESIS ESPECÍFICA N°2:

Around the turn o f the century there was a considerable amount o f experimental activity to discover the nature or otherwise of the anthropotoxin matter. Flugge (1905) shut individuals in a 3 m^ cabinet for up to four hours where the carbon dioxide levels rose to between 10,000 and 15,000 ppm. No discomfort was experienced and the ability to carry out mental work was not impaired as long as the temperature and humidity were kept at an acceptable level.

The results o f a series o f important experiments were published in 1913 (Hill et al). A 3m^ airtight chamber was used and 7 or 8 students were shut in until the carbon dioxide levels reached 3 to 4% (30,000-40,000 ppm) and the oxygen level fell to 16% from 17%, the wet bulb temperature rose to 82°F (27.8°C) or 85°F (29.4°C) and dry bulb temperature a degree or two higher;

students went on chatting and laughing, but by and by, as the temp rose, they ceased to talk, and their faces became flushed and moist. Some tried to light a cigarette (to relieve the monotony of the experiment) and were puzzled by their matches going out. They had not sensed the dim inution in the oxygen level which fell below 17%. T heir breathing was slightly deepened by the high percentage of carbon dioxide, but no headaches occurred in

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any of them from the short exposure to from 3 to 4 percent carbon dioxide. There discomfort was relieved to an astonishing extent by putting on the electric fans placed on the roof. W hilst the air was kept stirred the students were not affected by the oppressive atmosphere. They begged for the fans to be put on when they were cut off. The same old stale air containing 3 to 4 per cent carbon dioxide and 16 to 17 per cent oxygen was whirled, but the movement of the air gave complete relief The air o f th e cham ber breathed by other students outside caused no discomfort, yvhereas a student inside

breathing the outside air f e l t no r e lie f

The New York commission on ventilation (Winslow et a! 1923) carried out investigations both in the field (classrooms) and in the laboratory in an attempt to discover appropriate ventilation strategies. The studies took eight years to complete and examined effects o f the indoor environment on several aspects o f health and comfort. The team employed objective measures where possible such as the time taken for lifting exercises (rate o f work). They also used subjective scales for impressions o f odour, discomfort and warmth. The commission concluded that the thermal properties of the air are much more influential in comfort ratings than the chemical composition (carbon dioxide). The investigators designed two rooms; one referred to as the observation room had cooling and heating facilities and a ventilation system that could supply any quality o f air or even recirculate the vitiated air o f the room itself. The apparatus room contained the equipment for supplying heat and cooling to the observation room it also contained a window to view the occupants o f the observation room. Usually four subjects were present in the observation room. The results revealed that the chemical vitiation o f the air o f an occupied room is o f relatively slight importance. The organic substances present, manifest as body odours, may exert a depressing effect upon inclination to work and upon appetite; therefore, occupied rooms should be free from body odours which are obvious to anyone entering from without. The ventilation rate needed for this was found to be only 6 cfm per person or 3 1/s per person.

The field study part o f the commission’s report attempted to discover the relationship between odour and the prevailing carbon dioxide levels in classrooms by comparing different ventilation methods. The effectiveness o f window (natural

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ventilation) versus the effectiveness o f mechanical ventilation was thought to be an issue at this time and the commission carried out an intensive study to consider various ventilation strategies. In particular, four methods were identified for study; method 1 - window supply only; method 2 - window supply with gravity exhaust which tended to be an exhaust duct sited opposite the window and taken out through the building to roof level; method 8 - plenum fan supply with a gravity exhaust duct; method 9 - plenum supply with no exhaust. In practice, levels o f carbon dioxide did not reach the 5000 ppm limit that the commission considered likely to diminish occupant well-being. Observers were used to subjectively measure the levels o f odour and other environmental conditions. The observers spent one or two weeks continuously in the same classroom and remained in that classroom throughout the day noting their sensations o f the ambient air to odour, temperature, moisture content, and air movement. The observer was required to vote on an odour scale:

Odor

1. Especially fresh* 2. Odor absent* 3. Slight odor 4. M arked odor

These two scale points were used in summaries to indicate the absence of odour.

The study suffered from the use o f different observers for each evaluation. Figure 3.1 shows the number o f occasions (indicated as sessions) an observer judged classrooms to be free o f odours (vertical scale) with the ambient carbon dioxide levels shown on the horizontal axis for the four methods o f ventilation. Figure 3.1 also reveals that the majority o f sessions were regarded non-odorous or especially fresh. The commission could not relate the observers’ ‘especially fresh’ ratings to the levels o f carbon dioxide alone but suggested that a relatively low carbon dioxide level, low temperatures, varying air movement and with observers reporting that the space was ‘too cool’ were characteristic o f rooms considered ‘especially fresh’. Teachers were also asked to respond to the ambient air. The odour scale adopted for teachers was:

-a &3 UQ n> L.J o £ Z 400

9 Especially fresh or odour absent - method

B Especially fresh or odour absent - method 13 Especially fresh or odour absent - method B Especially fresh or odour absent - method □ Slight or marked odour - method 1 □ Slight or marked odour - method 2 Slight or marked odour - method 8 Slight or marked odour - method 9

500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700

Carbon Dioxide levels (ppm)

Figure 3.1: Number of sessions in which an observer judged the odour level in various classrooms. The methods refer to ventilation strategies: 1 Window supply, no exhaust, 2. Window supply, gravity exhaust, 8. Plenum fan supply, gravity exhaust, 9. Plenum supply, no exhaust.

Source: Winslow et al 1923 c c/2 n c > O

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General Air Condition