ULTRAVIOLET PROTECTIVE CAPABILITIES OF HATS UNDER TWO DIFFERENT ATMOSPHERIC CONDITIONS
M.G. Kimlin 1, * and A.V. Parisi1
1Centre for Astronomy and Atmospheric Research, Faculty of Sciences, University of Southern Queensland, Toowoomba, 4350, Australia. Phone 61 7 46 312727, FAX 61 7 312721. E-mail: firstname.lastname@example.org
* To whom correspondence should be addressed.
Ultraviolet protective measures for humans, such as hats, sunscreens and shade areas are all promoted by health promotion authorities as essential measures to reduce human UV exposure. Previous investigations have determined the effectiveness of various types of hats. Diffey and Chesseman (1992) found that the style and shape of the hat determines the protective capability of the various types of hats and the shape of the hat determines which facial sites receive the best ultraviolet protection. Wong et al., (1996) found that the protection factor for various hats in the southern hemisphere (as opposed to Diffey and Cheesemans northern hemisphere) was between 6 and 2 for various areas of the face. However, there is a lack of scientific quantitative data on the protective capability of hats under cloudy conditions compared to clear sky conditions. This paper presents the results on the effectiveness of hats to prevent UV exposure to facial areas during cloudy conditions compared to clear conditions.
2. MATERIALS AND METHODS
2.1 Polysulphone Dosimeters
The polysulphone was calibrated against a calibrated spectroradiometer (Wong et al 1995) with the erythemal UV exposure, UVery calculated using:
where A(l ) is the erythemal action spectrum (CIE, 1987), S(l ) is the spectral irradiance and T is the exposure period.
2.2 Erythemal Exposures
A rotating base with four upright human headforms was used to model random movements of a human in an upright position. Each head form, as shown in Figure 1, was located approximately 1 meter from other neighbouring headforms and this distance was selected to minimise the effect of reflections from the other headforms. Airey et al (1995) and Holman et al (1983) have compared human UV exposures to that of head forms and body forms and found that UV exposures to manikins can be related to human UV exposure. The headforms were rotated on a portable rotating base at a speed of approximately 1 revolution per minute in an open unshaded area, 50m from the nearest trees and buildings. The area was covered in grass with an albedo of approximately 3% at 60 cm from ground level as measured with a hand held erythemal UV meter. The albedo was calculated as the ratio of the upward and downward erythemal UV irradiance levels as measured with an erythemal UV meter (Model 3D V2.0, Solar Light Co., Philadelphia, PA).
In this paper, only the upright position of the headform is employed and no other head tilt positions are considered. Polysulphone dosimeters were placed at 16 sites on the headform, namely: vertex of the head, forehead, nose, chin, left cheek, left ear, right cheek, right ear, upper front neck, lower front neck, left neck, right neck, left shoulder, right shoulder, rear upper neck and rear lower neck. Sixteen dosimeters were selected so as to obtain a more accurate assessment of the UV distribution over the human face as the human face has a complicated topography and the high number of dosimeters used provides a better picture of the UV distribution of the human facial UV exposure.
These experiments were conducted at a sub-tropical southern hemisphere latitude in Toowoomba (27.5 oS, 151.9 oE), Queensland, Australia. The erythemal exposures were measured in autumn between 22nd April, 1999 to 28th May 1999 from 09:00 Australian Eastern Standard Time (EST) to 12:00 EST and in one hour intervals from 09:00 EST to 12:00 EST. To assess the effect of cloud cover, experiment periods were divided into two distinct cloud groups: firstly, no cloud or total clear sky conditions and secondly total cloud cover as determined visually by an observer with the solar disk obscured. The experiments with total cloud cover had the solar disk completely covered with cloud of the strato-cumulus cloud type. The average solar zenith angle for the measurement period was 46.6° and 21.5° for 09:00 EST and 12:00 EST respectively.
The three types of hats used in this study were a peaked cap, a broad brimmed woven hat and a broad brimmed "soft" hat. These will be referred to as hats 1, 2 and 3 respectively (Figure 1). These hats were selected for this study as they are worn by local schoolchildren. Figure 1 shows the shape and style of each of the hats. Hat 1 has a brim size of 7 cm, hat 2 has a brim size of 8 cm while hat 3 has a brim size of 7.5 cm and all are mounted at an angle between 12° and 18° to the forehead. The differing brim angles are due to the construction of the hats, where the brims are fixed to the crown of the hat at an angle. The rotating platform as shown in Figure 1 was designed so that 3 headforms with hats and 1 headform without a hat to act as a control could be exposed to solar UV simultaneously.
2.3 Ultraviolet Protection Factor
The ultraviolet protection factor (UPF) was calculated for each facial site as follows (Gies et al., 1992):
UPF = (UV Exposure without a hat)/(UV exposure with a hat) (2)
Figure 1 Rotating platform with the hats used in this study
3.1 Erythemal Exposures
Table 1 Relative UV exposure to selected anatomical locations without a hat
The erythemal UV exposure for various facial anatomical locations for clear and cloudy conditions from 09:00 to 12:00 EST is shown in Table 2 with 1 MED defined as 20 mJ.cm-2 (Diffey, 1992) and is the amount of biologically effective UV required to produce barely perceptible erythema after an interval of 8 to 24h following UV exposure. Table 2 also shows the effectiveness of hats 1, 2 and 3 under cloudy and clear sky conditions. The ambient UV level (as recorded on the vertex of the head with no hat) on the cloudy day was reduced by the cloud. The wearing of a hat does reduce the UV exposure to the face, but it is dependent on the type of hat used. Also the distribution of the UV under cloudy conditions changes when compared to clear sky conditions.
Table 2 Erythemal UV exposures using hats 1, 2 and 3 to various facial anatomical locations for clear and cloudy conditions
The removal of the direct UV component from the sun by cloud cover increases the percentage of the diffuse component of the UV (Blumthaler et al., 1994). UV protective devices, such as hats, rely on the interception of the direct component of UV to reduce the UV exposure. If the ratio of the diffuse to direct component increases, the ultraviolet protection factor (UPF) of the hat decreases.
The average UV exposure to the facial sites (forehead, nose, chin, left and right cheek, left and right ear) show that the exposures received, even in cloudy conditions and while wearing a hat can be high. For example, hat 2 had an average facial exposure of 2.5 MED while using the hat in sunny conditions between 09:00 EST to 12:00 EST, but in cloudy conditions with the same hat and time interval, the face received an average exposure of 1.7 MED. This suggests that although hats are effective UV protective devices, other UV protective strategies must be used in conjunction with the hat to ensure minimal UV exposure.
Table 3 shows the UPF for each of the hats used in this study in clear and cloudy conditions. The data in Table 3, shows the UPFs averaged over all anatomical sites for each of the three hats. The average UPF for each hat decreases with cloud cover. Hat 1 (the peaked cap) has the lowest average UPF of all hats (UPF = 2.5 for cloudy and a UPF of 3.2 for sunny) in this study. This result is to be expected, as the cap offers little or no protection to the ears, side of neck and rear neck when compared to hats 2 and 3.
Table 3 - The UPF of each hat in clear and cloudy conditions.
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