TO comment that "swimming is good for you" (Impressions, June 2) is less than satisfactory.

In the interests of future swimmers it is important to bring some important facts to the attention of those running the clubs and to those taking part:

1. It is not the presence of chlorine in the water that is the problem. It is depletion of chlorine that allows the build up of nitrogen tri-amines which goes into the air when the water is agitated with too many people in the pool along with excessive splashing, as seen in "fun pools".

2. Other than avoiding crowded pools, asthmatic children should follow the regime worked out in York for the prevention of what we thought was "exercise-induced-asthma" caused by the release of histamine from the large protective cells lining the breathing tubes.

In fact, there are probably other causes of cell damage in the lungs lower down due to the release of unwanted enzymes due to the effects of nitrogen tri-amines.

This is always damaging but can be prevented by correctly inhaling Intal before entering the pool (although those with asthma should not enter the toxic environment of an over-crowded pool).

3. A poolside warm-up session before swimming is always a good idea, but by a crowded pool.

Having taken these precautions it should, in my opinion, be safe for asthmatic children to enter the pool (always with two certificated live-savers around).

Sadly, Intal was taken over by Aventis who now have little interest in its production. There is too little percentage in it and asthmatic children do not figure highly on their list of priorities.

David Morris,

Priory Street, York.

Updated: 12:05 Friday, June 06, 2003