VENTILATION REQUIREMENTS IN CIVIL DEFENCE SHELTERS

Abstract

The ventilation requirements for survival in a civil defence shelter was studied in this project. Test subjects, consisting of local people, were tested for their physiological and psychological responses in a crowded, warm and humid environment in a thermally environmental-controlled chamber. The test subjects consisted of healthy males between 18-21 years old. Such chamber tests were conducted to simulate warm and humid survival environments in a crowded space, which can be encountered in fully occupied Civil Defence (CD) shelters. It can be expected that when people start entering a ventilated shelter, the temperature and humidity in the shelter will initially rise and then eventually reach a steady state. Should there be a disruption of the ventilation, the temperature and humidity would rise sharply. To study the human response under these situations, tests were conducted in a chamber where the shelter environment could be simulated. Three types of tests were conducted - transient state test (TST), where the chamber temperature and humidity was allowed to increase with time; steady state test (SST), where the shelter temperature and humidity remained constant; and buttoned-up test (BUT), where no ventilation was provided. In the transient state tests (TSTs), the chamber was supplied with outdoor air, which had been treated to conditions typical of the local weather. Different flow rates of the outdoor air were supplied into the chamber. In the steady state tests (SSTs), the condition of air in the chamber was maintained by varying the condition of the supply air. The duration of these tests was 3 hours. The duration of the BUTs, which was without ventilation, depended on the endurance of the test subjects and their agreement to continue with the test. The longest BUT conducted was 51 minutes. In the TSTs, the thermal environment in the chamber depends on the flow rate and the condition of the supply air. The most severe environment at the end of the 3- hour test duration was encountered when each person was provided with a ventilation rate of 16m3/h and the supply air was at 32°C and 0.02 kg/kg humidity ratio. The air motion was 0.3 m/s. The final oral temperature reached was 37.0°C and the effective temperature (ET) was slightly above the 32°C limit. However, the increase in body temperature, heart beat rate and loss in body weight were well within the safe limits. Increasing the air motion to 0.75 m/s did not seem to improve the thermal environment. The psychological tests conducted also revealed that the subjects were not adversely affected psychologically. In the SSTs, the thermal environment in the chamber was set at around the final condition in the TSTs. The most severe environment in the test was set at 35°C, 80% relative humidity and 0.25 m/s air motion (ET at 32°C). The body temperature stabilised after 50 minutes and remained at 36.9°C for the rest of the 3-hour test and the physiological indicators did not show any adverse condition. Similarly, the subjects were not adversely affected psychologically also. The test results in the chamber show that the ventilation rate of 16m3/h per person was sufficient for healthy young person to stay in a shelter. Increasing the air motion in the shelter did not have an observable effect on the test subjects. The concentration of carbon dioxide in the shelter was not a problem. In the BUTs, the air in the test chamber became laden with water vapour quickly and its temperature was approaching the mean skin temperature. The thermal environment was stressful at the end of the test that lasted 51 minutes, because the body could hardly reject the metabolic heat anymore. The air in the test chamber became almost saturated with water vapour, but the carbon dioxide level and the physiological stress indicators were still below their respective safe limits. In the BUTs, no adverse psychological effects were observed in the subjects. Based on the results of the chamber tests, similar tests were then conducted in both underground and above-ground civil defence shelters with full occupancy. Two types of tests were conducted in each shelter - the ventilated test and the buttoned-up test. In the ventilated tests, outdoor air was supplied at an average ventilation rate of 16.5 m3/h per person. In the buttoned-up tests, all the doors were shut and no ventilation was provided. The duration of the tests was 4 hours and approximately 90 minutes respectively. The results were analysed and evaluated as in the chamber tests. For the ventilated shelter tests in the underground shelter, the average shelter air temperature was 31.5°C and the humidity ratio was 0.024 kg/kg. The ET level reached 29°C and the body temperature stabilised at 37°C. The highest CO2 level reached was 0.12%, much lower than the acceptable limit for human survival. For the above-ground shelter tests, the average shelter air temperature was 32.5°C and the humidity ratio was 0.024 kg/kg. The ET level reached 29.4°C and the body temperature 36.9°C. All the physiological indicators were below the safe limits and psychological tests revealed no adverse effects. Hence the ventilation provided in the actual shelter is sufficient for a healthy young person. For the buttoned-up tests in the shelters, the highest condition reached was in the above-ground shelter, where the shelter air temperature reached 34.6°C and relative humidity of 98.1 %. However, the final CO2 level was 1.08%, below the safe limit of 3%. The ET level (34.4°C) exceeded the limit (where a normally clothed person can tolerate the physiological stress associated with this ET range of which 32°C is the upper limit) by 2.4°C for about 30 minutes in the test. However, the physiological indictors did not exceed the safe limits although the thermal conditions were stressful. No adverse psychological effects were observed.