As the tanker said, not only do you need to open up the tank/armored vehicle for various reasons, but if you are in a chemical battlefield and need to exit the vehicle when it is hit, exiting in to a chemically contaminated environment with your suit on will kill you. If you are suited up and just need to put on the mask you should be OK.
The WP chem suits were much more "rubberized" than the US/NATO gear and as a result were a real heat stress problem for Soviet troops.
I think that the use of chemicals is being taken far too lightly here. With the WP's huge inventory, its too much an advantage for them to use them without NATO being forced to go nuclear. And IIRC, using persistent chemicals is going to reduce Germany to something akin to an unlivable desert. It's one thing for chemicals to break down over time and be decontaminated and washed away by rain to use for military purposes. Its another to make even farmland fit for safe every day civilian habitation.
One of those 1980s era WWIII novels had the East German government telling Moscow that if they even remotely contemplated the use of chemicals the DDR would address the issue "with the utmost concern." IOW, they'd blow the whistle on the WP's plans for a surprise attack, reveal the false premise for the attack (a supposed West German terrorist attack in Pskov), AND reveal the true reason for the invasion: A muslim terrorist attack in Baku that crippled Soviet oil production.
Within the bowels of East Berlin, the realization was that a successful WP conquest of West Germany would mean German Unification under the DDR. But that:
"...a United Germany, even a United Socialist Germany, would be seen as a strategic threat to THE RUSSIANS!"
So...no chemicals. Unless the USSR's control over the DDR was so absolute that they (and Czechoslovakia and Poland and Hungary and Rumania and Bulgaria) would slavishly allow their ecosystems to be destroyed. After all, persistent nerve gas isn't WWI mustard or chlorine gas.