Do long sleeve shirts increase the risk of heat stress for outdoor workers?

 

short to long1

 

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
Air Temperature 39°C 39°C
Black Globe Temperature 40°C 40°C
Relative Humidity 65% 45%
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.

Bottom Line

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

http://www.cancer.org.au/about-cancer/what-is-cancer/facts-and-figures.html

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.

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8 Comments

  • Ken Bermingham says:

    Hi Ross,

    Thank You, this information is very helpful. One of the other requests that I often have involves the use of shorts V’s long pants, I think that if we applied the same principles to this ( shorts V’s long pants) scenario that the outcomes would be reasonably similar.

    Regards,

    Ken

    • Ross Di Corleto says:

      Hello Ken,
      There is a similar effect when you consider long trousers and shorts. The main difference is that there is a larger surface area associated with the legs so possibly more area to evaporate sweat and cool but also more area to be at risk of UV, cuts, abrasions & burns etc.

  • Ian Firth says:

    A very interesting article Ross. This is certainly a well aired concern by workers when asked to move to wearing so-called long-longs. I think that cancer risk wins – I would opt for the long-longs. Some of your previous discussions should also be considered though – colour of clothing (dark versus light), whether it is loose fitting or not, etc.

  • Scott says:

    I didn’t realize that companies were encouraging their employees to wear long sleeve shirts because they didn’t want them to get skin cancer. I can see why this would be an important safety tip. I’ll have to remember this if I’m ever outside for a long period of time.

  • Adam says:

    I think there are other factors to concider here.
    Think about what you would normally wear when your out on the weekend in 30+c heat, it probably won’t be pants and a long sleeve shirt.
    I come from a place that has drastic changes in temperature throughout the year aswell as on a given day.
    In winter it gets down to -12c at night and in Summer can be 40+c during the day so getting a custom to the heat can be tough.
    Another way to think about it is most sports people wear short length clothing while working. Why are construction workers forced to wear longs, Tiipcal nanna state crap.

    • Ross Di Corleto says:

      As indicated the data does indicate that there is a negative impact on ability to cool no one is denying that. Agreed as in most heat stress issues there are numerous things to consider. The blog merely points out that it may not be as large an impact as some believe. It comes down to a risk assessment that individuals and companies must make between the two key consequences and many consider melanoma a higher priority than the loss of cooling effect.

  • stevo says:

    I am a ceramic tiler and have been asked to wear long sleeves &long pants on site . scenario ; large unit complex working in bathrooms with no windows ,job site is in cairns far north queensland today ,6.30 in the morning inside temp 28.7c raining outside humidty would be around 85-90 percent could understand if working outdoors where sun protection is paramount .I will be employing a crew of around 12 men heat stress is a major concern. where does this leave employers? don’t want to be responsible for health related illness stress issues. I am all for safety of workers and ohs in some areas is all good but common sense must kik in .all comments greatly received

    • Ross Di Corleto says:

      I think this comes down to assessing which risk is likely to be the highest. As mentioned in another earlier comment, the long-longs policy in many industries relates to the risk of UV exposure but in some cases it can be for other reasons, i.e. protection from weld splatter, protection from cuts/abrasion injuries, as insulation from exposure to high radiant heat such as in foundries & smelter or protection from contact with hazardous substances etc. I would be assessing the key hazards/risks in the tasks being undertaken, prioritizing them, identifying potential controls and putting them in place. Depending on the scenario, the risk from thermal stress and its impact on the individual may justify short sleeves. There is quite a bit to this argument from both sides but ultimately the call needs to be made based on the risk to the health & safety of the individual. Is this a case of improving comfort at the expense of safety or is it a justified assessed thermal risk that needs to be controlled and going to shorts is the way to control it? That is the decision that needs to be made.

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