Re: how bad for the lungs can the chlorine of swimming pools be?

In answering your question on just how bad chlorine can be from swimming 
pools, I first need for you to be aware that there are many different forms 
of "chlorine" and some of these forms and compounds can be dangerous, not 
to mention all the other microscopic organisms in the water the chlorine 
kills.  Most chlorine forms and compounds that are in pools are considered 
safe for humans.  However, there are some chlorine forms that can be quite 
hazardous to the person handling them when using them.  One of these forms 
is chlorine gas.  Quite a number of large use pools (public and club 
swimming pools) use a system of sanitizing the pool water with chlorine 
gas.  Chlorine gas is a great sanitizer but also has several disadvantages. 
It's a gas that must be delivered in bulky metal cylinders, and when not 
stored properly can produce their own unique hazards.  The chlorine gas 
then has to be applied to the water through sophisticated metering systems 
operated by trained personnel. And it's highly corrosive, toxic, and very 
acidic - due to the H+ and CI - (muriatic acid), the byproduct of its 
reaction with water.  Most regulated pools are required to install separate 
feeding equipment to add approximately 1.25 pounds of soda ash to 
neutralize the acidity of one pound of chlorine gas.  

Even with tablet forms of chlorine, which can be added to private pools, 
one must use caution and always read the directions.  Always use care when 
opening a container of chlorine.  Have as much ventilation as possible when 
opening containers.  Breathing in chlorine gas can knock you right out, and 
could be fatal.  The chlorine gas can create muriatic acid within your 
lungs and produce measurable damage; but more importantly, chlorine gas can  
displace the air in your lungs and you can suffocate.  Always wear 
protective handling gear such as eye protection and rubber gloves.  If 
chlorine touches your skin, you should wash it off to prevent irritation.  
If chlorine splashes in the eye, irrigate with water and contact a 
physician straight away.  The label on the chlorine container will also 
tell you never, never, never mix chlorine with any other chemical.  You 
could produce a combustible or even explosive compound. This includes 
mixing two different types of chlorine, or chlorine and bromine.  Dirt, 
debris or any foreign substance (algaecides, alkalis and acids, etc.) can 
cause spontaneous combustion when mixed with chlorine.

Allergic reactions to chlorine are rare; however some individuals have 
experience skin irritation.  Extremely high levels of chlorine in the water 
could possibly release enough gas off of the surface in certain conditions 
to render breathing difficulties, but this situation is quite often rare 
and typically occurs with enclosed pools.

It is a common misconception that red eyes and a strong chlorine smell to 
the water is the result of too much chlorine. Actually, the cause is not 
enough chlorine! Free chlorine molecules, that is.  The combined chlorine 
compound, called a chloramine, is produced when a free chlorine molecule 
combines with a nitrogen or ammonia molecule.  Common nitrogen compounds 
come from human waste, such as perspiration, urine and skin proteins.  
These compounds smell bad, irritate the eyes and skin (far more readily 
than chlorine gas evolving from the pool water), and get in the way of free 
chlorine trying to do its job.

Shocking or super chlorinating the pool water is then necessary to oxidize, 
or break apart these compounds. So then, when the eyes burn, and the pool 
smells over chlorinated, the pool doctor's prescription is to raise the 
chlorine level ten times the normal amount to achieve "breakpoint 
chlorination" thresholds which will break apart the chloramine bonds. 

So in a way, chlorine can be harmful for your lungs; especially if you are 
handling the chlorine to treat pool water.  It's just not necessarily or 
directly from swimming.  Granted, there have been documented cases of 
individuals with allergic reactions to chlorine and some cases of damage, 
but only quite rarely.  More individuals die from bee stings than allergic 
reactions to chlorine.

The greatest factor in the creation of chloramines is the number of people 
swimming in a pool.  The greater number of people swimming in a pool, the 
more contaminants are introduced to use up the free chlorine molecules and 
create the irritating, bad smelling chloramines.  I'm sure temperature is a 
factor as more people are inclined to go swimming when the weather is 
hotter.

Finally, as with all things, there will always be a risk.  In swimming, 
there are always risks: the risk of drowning, hitting your head, etc.  The 
question is to put into perspective the amount of risk with everything 
else.  There is more harm from swimming in water that has not been 
sanitized properly, which contain all sorts of unhealthy micro-organisms 
(E. Coli bacteria for example), than the risks from injury in swimming in 
chlorinated pool water.

Technically I'm not one of the best indivduals to answer this question, but 
being a swimmer myself, I am all too aware of having burning eyes and at 
times becoming overwhemled by the smell of chlorine.  Hope this has helped 
answer a few of your questions.