Guidance for Expeditions

The primary source of medical guidance to expeditions in the UK is the Royal Geographical Society [RGS] . Their URL may be found on the useful links page.

In addition to the information included in the rest of this site there are some special circumstances which those organising, or on expeditions must bare in mind.

Key factors expeditions need to consider :

1. Acclimatisation Period

For safety the maximum acclimatisation period of 14 days should be adopted to allow for the wide range of people's individual acclimatisation times.

2. Work rate during acclimatisation

Athletes are given acclimatisation guidance based on :

However on expedition remember work generates much more heat .

Because the muscles used, and the ways they are used, are far less efficient than running and walking work is very different from these activities.

Work typically is 10% efficient compared to the athletic norm of 20% .

Chopping, dragging, carrying etc generate twice as much internal heat as running and walking for the same amount of external work.

Limiting work on expedition is difficult during acclimatisation

It is not practically possible out in the wild to count or judge, in the same way that athletes can, how much work, and hence internal heat, a person is generating.

Expedition organisers must be very careful of the activities undertaken during the acclimatisation period.

3. Pre exepdition health checks

Immediately before leaving on expedition, members should be asked to check off and declare formally any heat illness risk factors, or any other conditions which may affect their health. This allows leaders can keep an extra eye on those individuals. Those with colds and/or fevers should be prohibited from any significant activity until they are at least 5 days clear of the condition.

4. Training and awareness

The difficulty in controlling work rates means that heat illness is very likely when expeditions go to hot environments. This tends to be supported by RGS statistics where 14% of medical incidents in hot environments are heat related, even on well run expeditions.

All expedition members should be aware of the heat risks and how they arise so they can modify their behaviour to minimise risks.

If those with medical responsibility on an expedition do not have suitable wilderness medical training, then the expedition faces significant extra risk. Experience and background in civilised medicine is not sufficient. Inadequate knowledge and understanding of the special circumstances of the wilderness can be lethal in the field.

5. Humidity in the jungle

The University of Queensland Australia has shown that the relative humidity in the rain forest varies with the height of the forest. For example in tall dense jungle

Location Temperature Relative Humidity Amount of sunlight

Top of canopy

28 oC 60% 100%

Mid canopy

27 oC 80% 10%

Forest Floor

26 oC 90% 1%

If the tree cover and tree height is not enough to reduce sunlight by 99% then a full 30% difference in relative humidity will not be experienced. Using the table above the amount of sunlight falling on the forest floor can be used as a rough guide to the extra relative humidity likely to be experienced.

6. Frequency of medical incidents

The following table shows the frequency for various types of incident on expedition as derived from the paper "Expedition health and safety: a risk assessment" by Anderson and Johnson from the Journal of the Royal Society of Medicine.

Minor medical incident rate 6.4 per 1000 man days
1 per 156 man days
Serious incident rate

0.3 per 1000 man days
1 per 3250 man days
Sun/heat [minor and serious] 0.93 per 1000 man days
1 per 1075 man days

The rate at which serious medical incidents occur is 1 in 20 of the minor incidents, or 5%. The majority of these serious incidents result in evacuation.

The following table gives expedition sizes from 5 to 30 people, and shows the chances of there being an incident during the whole length of the expedition. Two durations are considered: 8 weeks which is about average, and 12 weeks.

Table: Chances of an incident by expedition size and duration

number of people

on expedition







Chances of a

serious incident

8 weeks







12 weeks








[minor and serious]

8 weeks







12 weeks







Chances of 2 evacuations within 24 hours of each other

Evacuations usually deplete an expedition's medical supplies and equipment as some have to accompany the patient who is evacuated. Because of this serious medical incidents can be much more demanding and riskier when they occur before the expedition's supplies are replenished. The following table gives an indication of the chances of both serious and minor medical incidents happening within 24 hours of an evacuation. The risk increases in proportion to the time that goes by before the expedition's medical kit is restored to normal provisioning levels.

Table: Risks of an incident within 24 hours of an evacuation

no people on expedition

5 10 15 20 25 30
Risk of serious incident within 24 hrs 0.2% 0.3% 0.5% 0.6% 0.8% 0.9%
Risk of minor incident within 24 hrs 3% 6% 10% 13% 16% 19%

6. Expedition planning

Planning should include medical supplies, evacuation plans and resources to cope with an evacuation within one day of another where the expeditions size indicates this would be a significant risk.

When planning evacuations allowance must be made for night time incidents when transport is often not possible. This is particularly true for night time evacuation from the jungle which is particularly hazardous. No helicopter pick up is possible due to the risk of the helicopter itself crashing if tangled in unseen vegetation.