Development and management of a radon assessment strategy suitable for underground railway tunnelling projects.

The construction of underground tunnels through radon-bearing rock poses a radiation health risk to tunnelling workers from exposure to radon gas and its radioactive decay products. This paper presents the development and practical application of a radon assessment strategy suitable for the measurement of radon in tunnelling work environments in Hong Kong. The assessment strategy was successfully evaluated on a number of underground railway tunnelling projects over a 3 y period. Radon measurements were undertaken using a combination of portable radon measurement equipment and track etch detectors (TEDs) deployed throughout the tunnels. The radon gas monitoring results were used to confirm that ventilation rates were adequate or identified, at an early stage, when further action to reduce radon levels was required. Exposure dose estimates based on the TED results showed that the exposure of tunnel workers to radon did not exceed 3 mSv per annum for the duration of each project.

Dust from cotton manufacture: changing from static to personal sampling.

Several designs of personal samplers were tested for use to collect cotton dust. The IOM personal inhalable-dust sampler was selected because: (1) collection of the whole inhalable fraction was preferred, since all inhaled sizes are under suspicion as contributing to respiratory symptoms in cotton exposure; (2) this sampler is well characterized; and (3) it was found to be practicable in the environments examined. Gauze shields to exclude 'fly' from the personal sampler were tried, but were rejected mainly because measurement of the whole inhalable fraction by a validated sampler was felt to be more appropriate. A range of processes at a representative selection of mills was assessed by a hygiene team, and classified as 'clean' or 'dirty' in terms of present standards of control. This classification agreed well with subsequent measurements using the present method, which uses a large static sampler. A personal sampling survey then showed that in about two-thirds of 'clean' processes personal exposure of at least 80% of those employed was less than about 2-2.5 mg m-3. Only one-tenth of 'dirty' processes met this standard. Personal exposure correlates poorly with the present static method, as expected, but comparison of the results suggested that a mean background level of 0.5 mg m-3 would correspond to a median personal exposure of about 2.2 mg m-3. Side-by-side measurements by the background method differed by less than 0.15 mg m-3 on about 95% of occasions. Niven et al. (to be published) have compared the IOM head used in this study with the Manchester University sampler previously used by Cinkotai et al. [Ann. occup. Hyg. 32, 103-113 (1988)] to derive a relationship between personal exposure and prevalence of byssinotic symptoms in spinners. According to Cinkotai et al.'s results the concentrations of 2-2.5 mg m-3 discussed would correspond to a prevalence of 3-5%. However, this prevalence probably reflects higher exposures in the past.

Airborne fibre levels associated with the use of MMMF brazing mats during welding operations.

In 1985 the Health and Safety Executive set a gravimetric Control Limit for airborne Man-Made Mineral Fibre and in 1987 a respirable fibre number Recommended Limit for Superfine MMMF. A limited investigation was carried out of the use of glass and ceramic fibre products used as protection against welding 'batter' and oxyacetylene welding flame. Airborne fibre levels are compared with the Occupational Exposure Limits.

The time course of mandelic and phenylglyoxylic acid excretion in workers exposed to styrene under model conditions.

Urinary excretion of mandelic and phenylglyoxylic acids by two technicians building glass-reinforced plastic boats has been measured over a 7-day period. Peak excretion of both metabolites occurred several hours after the end of exposure. There was little relationship between urinary mandelic acid concentrations measured at the end of shift and the maximum excretion observed in samples collected after this time. It is suggested that sampling strategies devised to monitor workers exposed to styrene should reflect maximum excretion rates of urinary mandelic acid.