Because it indicates a corrosive atmosphere that could be hazardous to the health of anyone entering it? The facility has a process containment problem, if this is the case.

See #2↑. This reader's facility is leaking too much chlorine, and no-one would want to breathe that in!

This sort of thing highlights the need for sufficient process containment to reduce or eliminate health hazards from operational activity.

There are some buildings with only centralized air stack and no way for the trapped gases to escape and some people accidentally release large amount of toxic gases like Ammonia and Chlorine and some time SF6 and Organic Gases. Some processes can generate high levels of NOx, N2H2, SO2, O3, H2S etc. There were deaths due to such releases of toxic gases many times in industries and also in research organizations. Worst case was Bhopal Tragedy - Union Carbide Plant.

Many companies do not install monitoring and safety devices very deliberately and if asked then they say they have no such problem. Some time ago I visited Codak film plat at Malanpur near Gwalior, MP, India and it was out right smelly and they say they have no problems. I just could not hold on even for minute there. Horrible.

I think less than 10% people really install sensors and control systems. Most of them think it is a wrong investment.

Then the facility has a serious PROCESS MATERIALS CONTAINMENT PROBLEM! Go and sort it out, before someone gets sick/hurt/killed!