By Vivien Lee
The danger of sunburn for construction workers is just as high in autumn and winter as in spring and summer, a researcher told the Australian Institute of Physics Congress in Melbourne.
Just as skiers need to be careful of UV rays reflected off snow, she said, construction workers run the risk of exposure from light reflected by metals on the building site. And in winter they’re less likely to be wearing sunscreen.
Joanna Turner, a PhD student at the University of Southern Queensland, attached radiation-detection devices to mannequins placed in front of vertical reflecting surfaces. She discovered that those near zinc aluminium, commonly used in construction, experienced between 20% and 50% more UV exposure than those out in the open.
But this level of exposure depends on the season. Surprisingly, solar reflection is less significant in the warmer months. In spring and summer, the angle of the sun to the ground causes more widely-scattered reflection, leading to little difference between open air exposure and that near vertical surfaces. In autumn and winter, however, the reflected UV rays are preferentially concentrated in one direction which boosts exposure levels.
“The message for construction workers is to take care to wear sunscreen all year round. Reflections in the construction environment may allow sunburn to sneak up on them when they least expect it,” Joanna said.
Further information:
Ultraviolet reflection and outdoor workers: Why warm seasons have less influence on reflected UV exposures than cool seasons
Joanna Turner1, Alfio V Parisi 1
1University of Southern Queensland, Toowoomba, Queensland, 4350.
Abstract summary:
UV reflection from vertical metal surfaces can potentially increase cooler seasonal UV exposures. Proportions of direct to diffuse UV radiation, surface type and wall structure are proposed to contribute to this observation.
Abstract:
I. INTRODUCTION
Australia is known to have high ambient ultraviolet (UV) radiation with the result that outdoor workers are constantly exposed to this radiation. Previous studies have shown that up to 90% of workers in an outdoor environment experience UV exposures in excess of that stipulated by the National Health and Medical Research Council (NHMRC) [1]. This research was carried out during the period of September to November, spanning the whole spring season.
Previous work has been carried out on exploring the issue of reflected UV radiation, particularly through that of the exposures obtained by a construction or outdoor worker. It has been shown that common building materials used in Australia such as sheet metal is a high UV reflector and can increase exposure to the face of a construction worker by up to fifty percent [2]. The ability of a vertical surface to influence the UV exposure to a worker depends on a variety of factors, including solar zenith angle (SZA), orientation and direction of the surface and the type of surface being used [3]. As a result of recent studies, the difference between the influence of reflective surfaces to personal UV exposure in different seasons indicates that reflective surface capabilities in cooler seasons are more likely to be of concern than compared to that in warmer seasons. The current hypothesis for this occurrence is attributed to proportions of direct and diffuse UV irradiance in a given season, and the ability of a particular surface to reflect one or both types of UV irradiance.
II. METHODOLOGY
The influence of UV reflective surfaces on personal UV exposure was determined with the use of polysulphone dosimetry and head form manikins, to simulate head form and shape. Dosimetry is an accepted technique in approximating erythemal UV exposure to the body. One head form was positioned in front of a north facing UV reflective wall, while the two remaining head forms were used as controls, one located in front of a non-UV-reflective wall and one not located near any type of wall. Each headform had thirteen dosimeters attached in standard face and body positions and were calibrated against a scanning spectroradiometer located on a nearby building (Bentham Instruments, Reading, UK).
At the same time, spectral irradiance measurements were carried out using a USB4000 Plug-and-Play spectrometer (Ocean Optics, Inc., USA), including UV irradiance reflected from the UV reflective wall, global UV irradiance, direct sun UV irradiance, UV irradiance from the level of the horizon, specifically the UV irradiance opposite to the wall, and the UV irradiance where no wall is present. Analyses of these spectral scans indicate the importance of direct and diffuse UV irradiance.
III. HYPOTHESIS The reflective behavior of surfaces has traditionally been measured using albedo which is essentially the ratio of upwelling irradiance to downwelling irradiance. Unfortunately, this measure fails to properly account for the physical reflection characteristics for vertical surfaces, and particularly those surfaces which appear to reflect diffusely, but may be reflecting specularly or a combination of the two. In addition, with both direct and diffuse irradiance present in the atmosphere, the actual mechanisms occurring in the reflective process are difficult to define but may explain why seasonal changes in UV reflective capabilities are observed in some surface types.
REFERENCES
[1] Gies, P & Wright, J (2003) Measured solar ultraviolet radiation exposures in outdoor workers in Queensland in the building and construction industry, Photochem. Photobiol., 78(4), 342-348. [2] Turner, J & Parisi, AV (2009) Measuring the influence of UV reflection from vertical metal surfaces on humans, Photochem. Photobiol. Sci., 8, 62-69. [3] Turner, J, Parisi, AV & Turnbull, DJ (2008) Reflected solar radiation from horizontal, vertical and inclined surfaces: Ultraviolet and visible spectral and broadband behaviour due to solar zenith angle, orientation and surface type, J. Photochem. Photobiol. B., 92, 29-37.Contact:
Joanna Turner, joanna.turner@usq.edu.au