Dehydration

Dehydration can seriously affect an employee's ability to function safely when under thermal stress. Also you need to be aware that over a working week individuals who are particularly heat stressed may lose between 4-7% of their overall weight from the effects of dehydration. This level of water loss cannot be tolerated if a decent rehydration regime is not in place. Also you should be aware that thirst is not a good indicator of dehydration as if you are thirsty you are already starting to suffer from the effects of dehydration.

Strategies for minimising the effects of dehydration in heat stress situations are for example:

Encouraging employees to drink cool water (ideally at 15 ° C) rather than tea, coffee or carbonated drinks frequently in small volumes to compensate for losses due to sweating.

Using urine colour as a crude indicator of the level of dehydration ie the darker the urine the greater the dehydration and therefore the greater the need to rehydrate. Although you should take into account the effect of certain foods, for example beetroot can cause urine to appear much darker and suggest an individual is dehydrated when there is no cause for concern.

A typical hydration regime when working hard in heat stress conditions would be to drink around 250 ml (half a pint) every 15 minutes or 500 ml (a pint) every 30 minutes. This approach may not be practical if an individual has to wear PPE that restricts the ability to drink or where hygiene requirements prevent the consumption of food or drink. In these circumstances an alternative approach is drinking 500 ml of water per hour before work commences and encouraging the drinking of 500 ml of water during their rest periods.

This may meet their water demands during the work period but if water loss is significantly greater, then water intake should increase proportionately. Also even if workers replenish the lost sweat with equal amounts of water, they may still be susceptible to dehydration due to salt losses caused by excessive sweating. This means that before they start work they should ensure that they are adequately hydrated.