Anne:
Just a quick clarification or two:
1. Halon 1211 or 1301 and dry chemical extinguishers are TWO COMPLETELY DIFFERENT extinguishing methods. Dry chemical (Ansul 101 or 102, etc) is a powdery substance, pretty messy when it is released, and could potentially impair visibility, etc.
Halon is a gaseous supression agent and, although, when released, could theoretically cause a small percentage of obscuration, it is definately not enough to seriously impair your vision.
2. It is highly unlikely than anyone, including the pilots, would be exposed to Halon in concentrations great enough to cause dizziness, etc. It takes prolonged exposure at very elevated concentrations to do this. Even total flooding halon systems, which were used in the past as the main means of fire protection in vital computer operations, etc. were only designed to hold 5-6 % for 10 minutes. Trust me, sealing a room tight enough to hold that concentration is a job in itself! The 5-6% concentration is considered a "safe" concentration, and during the good ol' days when Halon was readily used, I have seen many a Tech actually stay in the room during discharge testing. It takes 11-13% for a prolonged period to have any physical side effects.
There isnt enough Halon in those extinguishers to get the concentration up that high in the cockpit. And, if by some chance there where many multiple extingishers set off in the cockpit at the same time, tell the pilots to just open the door! I guarentee that will dilute the concentration to "safe" levels.
The biggest danger a pilot has from a Halon fire extinguisher is being hit over the head with it

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3. I am not sure where the individual airplanes are with it, but since the days of the Montreal Protocol, Halon have been on the "endangered species", and now on the "extinct" list. It is no longer manufactured. Many Halon systems and fire extinguishers are slowly being replaced by FM200, Intergen, or other types of gaseous supression systems. So, there is a good chance that the extinguisher may not even be a Halon one anymore.
You may want to go back and check the article. The manufacturer may be talking about a total flooding extingishing system, not just a halon extingusher. Or, he may be selling Intergen

.
If you give me a link I would be glad to check it out and give you a "professional" opinion.
Regards,
Trudy