Gasmasks?

It's been a long time since I saw this movie and if I remember correctly, there is a scene where Lee Majors, a woman and some others break into somewhere to steal the diamonds. They are all wearing black leather jackets and gasmasks. Why are they wearing the gasmasks. I dont remember any gas in the movie at all. Was it so that they wouldnt be recognised. Can anybody explain please?

Sneaking around in gasmasks is near impossible so why would they do it in this movie. A year ago myself, my wife and two other married couples all went and played paintball skirmish against four people that we didnt know. All six of us wore Russian gasmasks (bought from a disposal store after 9/11) complete with corrugated breathing hoses and filters. We never won a battle all day as the enemy could always hear us breathing and yelling muffled orders to each other. We had no peripheral vision and were constantly ambused or 'out shot' in a gunfight as we could hardly see at times. We were slaughtered in our suits and gasmasks.

So why did they wear gasmasks in the film, any explanation?