Radon emanation of building material - Impact of back diffusion and difference between one-dimensional and three-dimensional tests

Small-scale chamber experiments were conducted to investigate the radon emanation rates of commonly used building materials such as bare concrete, granite, red brick, and sand brick. It has been found that back diffusion caused by the accumulation of radon in the indoor environment has significant influence on the radon emanation rate. The radon emanation rate can be expressed as the summation of an initial emanation rate and the product of a specific back diffusion coefficient and the indoor radon level, In some occasions the radon emanation rate can be significantly lower than its initial value. A database was developed summarizing results from 26 samples. The influence of relative humidity on the radon emanation characteristics has also been discussed. Separate tests were done by coating the four sides of the building material with silicone gel to simulate a one-dimensional radon diffusion geometry. The results show that a factor has to be included when the three-dimensional test results are used to describe one-dimensional geometry, such as radon emanation from building wall surfaces

Influence of different indoor activities on the indoor particulate levels in residential buildings

This study reports 24-hour measurements of indoor particulate levels in 8 residential premises in Hong Kong. The 24-hour respirable suspended particulate (RSP) levels varied from 44.9 to 119.4 mu g.m(-3) and the corresponding total suspended particulate (TSP) levels varied from 45.8 to 122.2 mu g.m(-3). These levels are higher than those measured in other countries. This was found to be related to the poor quality of outdoor air found in Hong Kong and also to the different indoor activities practised by these families. During the measurements indoor activities were recorded and ventilation rates at some of the sites were also measured using the carbon dioxide decay technique. A significant rise of particulate level was detected during cooking, smoking and burning of incense. In the study, particulate levels over 5,000 mu g.m(-3) were observed during some cooking activities. Particulate levels when people were smoking were 2-3 times higher than the relative background level. Incense burning in some families produced a peak concentration of particulates around 2,000 mu g.m(-3) if the ventilation was poor. The effect of rain was to wash the outdoor particulates from the air and at the same time the indoor particulate level fell if the ventilation rate was high enough. It was observed that about 20\% of the indoor dust level could be reduced in less than 1 h when there was heavy rain. It was also found in the study that a very high indoor RSP to TSP ratio of 82-98\% existed indoors

Influence of ventilation on indoor radon level

Detailed radon measurements were conducted at different residential units in Hong Kong in winter time when air-conditioners were off and also in summer time when air-conditioners were on. Ventilation rates were measured concurrently to investigate the influence of ventilation on indoor radon level. The ratio of indoor radon level to outdoor radon level was plotted against ventilation rate, and it was found that a critical value existed after which the indoor radon level could be considered identical to the outdoor level. This result is important for use in ventilation design to reduce indoor radon pollution. (C) 1997 Published by Elsevier Science Ltd

Indoor perchloroethylene accumulation from dry cleaned clothing on residential premises

Perchloroethylene in the residential environment mainly comes from dry-cleaned clothing. The study aimed at determining the respective perchloroethylene levels and their decay characteristics in three bedrooms set-ups which represented typical Hong Kong domestic premises. Selection of the bedrooms and choices of dry-cleaned clothing arrangement were based on results from a territory wide telephone survey. Two of the bedrooms had window type air-conditioning units installed, and one relied on natural ventilation for the air movement. Four identical tests were conducted at each site including change of quantity of the dry-cleaned clothing, and the option of removing or not removing the plastic bags which came from the dry cleaning shop. The clothing was located inside the wardrobe and charcoal tubes were connected to a mini-vol pump in order to collect 24-h samples in the bedrooms for further GC/MS analysis. Each test lasted for seven days and characteristics of the window and door opening habits were recorded. Perchloroethylene level as high as 494 mu g m(-3) was found in the site where the occupants seldom opened the windows. In other sites where more frequent window opening were conducted, the indoor perchloroethylene levels varied from 0.93-29 mu g m(-3) depending on the quantity of the dry-cleaned clothing being used. A clear decay curve was observed in cases where the plastic bags were removed before the clothing were put into the wardrobes. For cases where the plastic bags were not removed, the perchloroethylene level went up first in the first few days and then decayed in the subsequent days. The findings provided preliminary information of the health risk that the population may be exposed to due to their different practices of dry cleaning activities. The study was different from traditional chamber tests which might aim at identifying perchloroethylene emission from dry-cleaned clothing, nor was this study the same as other field measurements which reveal information of perchloroethylene levels in uncontrolled conditions. The study combined features of both field measurements on real domestic premises and controlled experiments based on results from telephone survey analysis. (C) 1998 Elsevier Science Ltd. All rights reserved