Understanding Shadecloth Protection
A Breakdown of Shadecloth Protection
The true value of shadecloth is measured by the amount of Ultraviolet Radiation Protection (UVR) it provides. To measure this, a special scale has been developed called the Ultraviolet Protection Factor or UPF[1]. UPF is used to rate materials and is directly comparable to SPF which is used to rate sunscreens[2].
A cloth rated UPF15 will provide 15 times the skins natural protection to Ultraviolet Radiation. In practical terms this means a person who on a hot summers day receives their daily recommended dose of UVR[3] in 10 minutes[4] could, by being directly under a shadecloth sail rated at UPF15 have 15 x 10 minutes or 150 minutes protection.
Selecting the right type of shadecloth
Today, the minimum UV shadecloth rating we recommended is 90%. Typically a 90% shadecloth gives a UVR of 10 which the Australian Radiation Laboratory classes as only "Moderate" protection. In the publication Under cover, Guidelines for shade planning & design [5] the recommended minimum rating for shadecloth has been stated at 94% protection to direct UVR.
|
Shadecloth UV Rating |
Shadecloth UPF |
Protection Category[6] |
|
85% |
6.7 |
- |
|
90% |
10 |
Moderate |
|
95% |
20 |
High |
|
95.9% |
25 |
High |
|
96.7 |
30 |
Very High |
Calculating the UPF when only the UVR is known
100 - UV rating = (a)
100 / (a) = UPF
Eg. Calculations for a 94% UV rated cloth.
100 - 94 = 6
100 / 6 = 16.6
Therefore, as a general guide, a 94% UV rated cloth would give a person 16.6 times their normal protection to Ultraviolet Radiation.
[1] Developed by The Australian Radiation Laboratory (ARL).
[2] ARL states that their rating system was developed for personal clothing however it is reasonable to apply the UPF rating to fabric so long as it is clear that the rating only applies to the material used in the construction of the item and not to the item as a whole.
[3] Called a MED or Minimal Erythemal Dose which is the amount of exposure to UVR required to produce the first detectable reddening of the skin.
[4] In Sydney on a hot summers day between the hours of 10am and 3pm it can take just 11.7 minutes to exceed safe exposure to the sun. In winter during the same hours it can take 120 minutes. These figures are based on IRPA figures measured in 1989.
[5] Greenwood JS, Soulos GP, Thomas ND, Undercover: Guidelines for shade planning and design. NSW Cancer Council & NSW Health Department Sydney, 1998.
[6] As described by The Australian Radiation Laboratory.
