Pavel314 wrote:
The building I work at was evacuated on Tuesday and shut down on
Wendnesday after about 20 people in one area got sick; they were
dizzy and nauseated enough to be taken to hospitals.

The hazmat team from the fire department checked everything and came
to the conclusion that it was nitrates and nitrites contaminating one
of several hot water heaters in the building. Apparently the people
in the area supplied by that heater used the hot water from the tap
for cooking or making tea and cocoa drinks.

My first thought was that a gasket or seal gave out, allowing the
water to contact the contaminants, but I can't see why a water heater
would have large amounts of nitrates and nitrites involved. Maybe
someone on the group with experience in large-scale water heaters for
an office building would know.

Someone in our department thought it might be a water softener system
problem; maybe someone grabbed a bag of fertilizer instead of rock
salt for the flush and wash cycle, but we're on city water and water
softeners are generally used with hard well water in my experience.
Plus, would they have a softener servicing only the water heater and
not the whole line, hot and cold?

My wife, who watches a lot of Miss Marple type mysteries, thought it
might be somebody trying to kill his girlfriend who works there, but
contaminating a hot water heater seems a far fetched plot. He'd have
to know which heater served her break room area and get by the
security desk in the lobby. Plus, from what I know of water heaters,
getting the contaminants into the heater would not be easy.

Any thoughts? If we hear how it happened, I'll post an update.

The hot water supply, because it isn't hot enough, is a frequent source of
all manner of nastiness. The nastiness, however, is usually of the bacterial
variety.

In your case, because folks suffered a chemical contamination, the hot water
system is merely one possibility, not the prime one.