Many companies are now insisting that their employees wear long trousers and long sleeved shirts when outdoors. Sometimes the justification relates to safety reasons such as protecting workers from cuts, scratches or contact burns from hot surfaces. Most often though it is because of the risk associated with exposure to ultra violet light and the potential resulting consequence of skin cancer.
A common outcry from the employees is the fear that it will intensify the heat load and hence result in an increased risk of heat stress. So is this concern warranted? Is it valid or one of those industry myths we often hear about?
If one was so inclined it is possible to look at this from a highly technical aspect, track down the relative insulation factors, effective insulation factors, water vapour permeability, water vapour resistance and garment shape and size. There are many technical reports that will provide this detail (ISO 9920 is a good start). There is however a simpler way to get a pretty good estimate without going to quite that length of analysis.
First of all we need to get hold of the thermal insulation of the clothing in question; this is measured in “clo”.
For underpants, shirt with short sleeves, light long trousers, light socks and shoes we have a combined result of 0.5 clo
For underpants, shirt with long sleeves, light long trousers, light socks and shoes we have a combined result of 0.6 clo (both measures from ISO 9920)
Next we utilise a heat stress index which can take into account the temperature, humidity and work being done and duration. In this case we will use Predicted heat strain (ISO 7933) as it fits the bill as it allows us to approximately predict the impact on the body’s core temperature (plus I have a program that will do the calculation for me). We will use two environmental scenarios and the two clothing combinations above and a core temperature limit of 38°C.
|Scenario 1||Scenario 2|
|Black Globe Temperature||40°C||40°C|
|Air Velocity||0.5 m/s||0.5 m/s|
|Metabolic Rate||175 W/m2||175 W/m2|
|Short Sleeve||Exceeded at 31 minutes||Not exceeded|
|Long Sleeve||Exceeded at 29 minutes||Exceeded at 174 minutes|
In Scenario 1, with a higher relative humidity the difference is minimal, approximately 2 minutes for the estimated core temperature to reach our limit value of 38°C. There is little additional stress from the long sleeves. Both scenarios show elevated heat stress and need to be addressed.
Scenario 2 is a lower humidity environment and for the short sleeves, the benefit of having more skin open to the air for evaporation of sweat is apparent. Bear in mind here that the long sleeve scenario still allows almost three hours of continuous work before some action needs to be taken.
So what is this information telling us?
- The short sleeves provide some additional benefit in lower humidity scenarios
- This is not as significantly in higher humidity climates.
- The environment plays a bigger role in the heat stress than the clothing.
There is some benefit from using short sleeves in the right climate but this needs to be balanced off against the other risks associated with cuts, abrasions, burns and cancer. This is a growing risk with workers that are employed for periods outdoors. In 2010 there were 11,405 new cases of melanoma diagnosed in Australia and 1544 deaths in 2011 (Cancer Council Australia). It is estimated that 73,870 new cases of invasive melanoma will be diagnosed in the US in 2015 and 9,940 will die from melanoma in the same year (American Cancer Society).
This is a trial with limited scenarios and for greater confidence a detailed assessment would require more scenarios with variable air velocities and a wider range of varying temperatures and relative humidity. However, it does provide some indication of the impact of short/long shirts.
Increasing the length of clothing can have a negative impact, increasing heat stress but to a limited amount and very dependent on the environment. This needs to be weighed up against other risks associated with cuts, abrasions, burns and cancer.
Want to know more?
American Cancer Society. Cancer Facts & Figures 2015. http://www.cancer.org/acs/groups/content/@editorial/documents/document/acspc-044552.pdf. Accessed July 6, 2015.
Cancer Council of Australia
Accessed July 6, 2015.
Sinclair, W. H., Brownsberger, J. C., (2012). Wearing long pants while working outdoors in the tropics does not yield higher body temperatures. Aus & NZ. J. Public Health, 37:1 pp 70 – 75.
ISO 7933 (2004). Ergonomics of the thermal environment – Analytical determination and interpretation of heat stress using calculation of the predicted heat strain. International Organization for Standardization, Geneva.
ISO 9920 (2007). Ergonomics of the thermal environment – Estimation of thermal insulation and water vapour resistance of a clothing ensemble. International Organization for Standardization, Geneva.