Today seafarers are less exposed to heat on board ships than in the former time of coal heated steamers. The engine rooms today have ventilation systems and are kept reasonably cool. However, when sailing in the tropics, sport activities ashore and hard physical labour on board and in ports may cause maritime workers to be exposed to harmful heat.
Although the origins of human life were in the tropical regions, modern man is better able to cope with cold environments than with extreme heat thanks to clothes and other kinds of insulation. However, besides falling into water, long lasting unconsciousness and drug intoxication may still cause seafarers to be victims of hypothermia.
The conditions caused by heat may, as described in the section below, be serious and life-threatening. There are well-documented cases of fatal incidents on board merchant ships also in recent years. They have occurred in excessive hot engine rooms but also among seamen who were working on open deck under excessive temperatures and without access to shade. Young and previously healthy seamen may be hit by heat cramps, heat collapse and even fatal heat strokes. Chronic diseases and other pre-existing conditions may although worsen the prognosis.
If the ship sails from a warm to a hot climate, the crew will have good time for acclimatisation. The body needs approximately about five days to adapt to a different climate, but some individuals may need up to a couple of weeks. It is therefore a special risk factor if crew members are flown from a temperate climate into a very hot area and start to work right away.
The aim of the acclimatisation is to be able to sweat more than normally, to reduce the loss of salt when sweating and to be able to redistribute the body heat and in this manner reduce the body temperature. These measures will reduce the risk of excessive body temperatures.
The seaman going to a hot area should try to start the acclimatization several days before the arrival to the area. This may be achieved by actually being exposed to increasingly higher temperatures. The same effect can be achieved by physical training. One should also get used to a high fluid intake. An intake of 3 to 5 litres per 24 hours is needed when working under high temperatures. Thirst is in a hot climate not a reliable sign that a person needs fluids. Extra salt intake is recommended. This may be achieved from salty foodstuffs like chips and sausages and by directly adding salt to the food. Seamen at special risk should be especially careful. Seamen with cardiovascular disease, chronic lung disease, and overweight and on certain medications (diuretics, antihypertensive and certain medicines used for treatment of neurological and psychiatric diseases) should be extra careful.
When in the hot climate, it is of importance to drink water all day through, also in the early mornings and late afternoons and evenings. During the hottest period of the day, sweating may far exceed the stomachs capacity to absorb fluids and dehydration will take place if no precautions have been taken. Intake of fruits may be important as it is an important supplement of other salts not present in ordinary salt. Drinks with high sugar content, like some “sport drinks”, should be avoided.
When working in hot climates, light, loose-fitting clothing will allow perspiration to evaporate and cool the body. Wide-brimmed hats in light colors keep the sun from warming the head and neck. Detailed planning of the work on board is essential. Long periods of work in the engine room should be avoided. Those in charge of the planning of the work should ensure many breaks with access to fluids and cooler surroundings. If work on open deck is needed, for example during prolonged mooring operations, there should be arranged access to shade and fluids.
Alcohol is seldom available on ships today, but if available, it should be avoided when working in hot climates. Also caffeinated drinks and heavy meals should be avoided. All crew members should be instructed in looking after each others and be aware of the first signs of serious conditions due to heat exposure like heavy sweating, paleness, muscle cramps, tiredness, weakness, dizziness, headache and nausea or vomiting.
The heat in the human body comes from the metabolism of nutrients and physical activity. The body can receive heat from external sources (sun, stoves etc) and it can lose heat to the environment (cold weather, being in the water, sweating etc). A thermostat in the brain keeps the temperature of our inner body – the core temperature- nearly constant. The main regulatory mechanism is to increase the blood flow to the skin, and to reduce the speed of the blood flow. If this appears to be insufficient, the production of sweat will be increased. The sweat requires heat to evaporate and this heat is taken from the skin. The sweat contains water and salts that are then removed from the body and the body may become depleted. To prevent depletion it is necessary to increase the intake of water and salt. If the intake of salt and water is insufficient, the kidneys will reduce the excretion of salt and water. The excretion of water in the gut will also be reduced, something which may lead to constipation. If these regulatory mechanisms are insufficient, blood will be re-directed from the skin to the brain and to other vital organs. The sweating will then subside and the temperature will rise. This is the mechanism behind the heat collapse and the heat stroke (see below) .