Optima indeed has a web site at
http://www.optimabatteries.com/main.htm

It has some good FAQs, but unfortunately none answers the
question at hand.

Speaking of fumes, I assume that is of more interest to us
with our batteries essentially in the interior with us.
This got really interesting for me once when my Bosch
battery literally exploded!  Turned the key and boom!  My
'81 is a vinyl seats/rubber floor version and the interior
acoustics are superb as regards explosions.  When I
recovered I realized I wasn't on fire and the smell was only
(?) battery acid.  This happened in the parking lot of my VW
parts store (Foreign Aide) so I went back in and bought a
new battery from them, installed it with a wrench they
loaned me, and was on my way in no time at all.