will be adequate because the salt in our food should replace that lost in sweat (assuming you eat a regular, balanced diet).
If exercising and sweating profusely for more than an hour, 150-200 mls of fluid every 20 minutes is wise. The fluid should contain some salt to replace that lost as sweat (e.g. a sports drink), or the person could eat salty snacks (but this is not practical on the fire ground unless resting and in a hygienic environment). This will help prevent both dehydration and hyponatremia. Also, a sports drink contains carbohydrate, which provides energy and helps to absorb water salt.
You should not drink any more than 1 litre per hour - this is heading towards excessive fluid intake.
The signs and symptoms of heat exhaustion and heat stroke are similar to that of hyponatremia, and can be confused. The symptoms of heat exhaustion include dizziness, headaches, nausea, fatigue and muscle cramps. Heat stroke includes the above symptoms, but will be accompanied by mental status changes, such as who they are, where they are, and what day it is. Somebody suffering from heat stroke will also have an excessive body temperature. With hyponatremia, people also feel very ill and experience mental status changes, but do not have the same high body temperature as with heat stroke. They also vomit forcefully and repeatedly and, unlike those with heat exhaustion, do not feel better by resting or cooling off. It is therefore important to be prepared and be aware of the physiological situation of yourself and others.
If you notice any of the above symptoms in yourself, or someone you are training or working with, stop what you are doing immediately and get into the shade. A good idea is to fill a bucket with cold water and submerge the hands of the affected person up to just over the wrists in it. Then seek immediate medical attention.
