For your needs Do NOT by a mask, you need to buy an "Escape hood". While many here will argue that a mask is cheaper if used repeatedly (it is) it takes more training, fitting(one size does NOT fit all), selecting of cartridges and practice donning ...to be effective...than people realize.
....To be effective......you do want it to be effective right?
An escape hood is meant to be used in the exact situation you have described.
>It needs no fitting, you pull it on right over your head, it can be used over beards, a two day stubble, eyeglasses, long hair, male or female and is less clautraphobic.
>You don't have to fumble attaching filter cartridges (cartridges begin to expire as soon as they are taken out of the package) that is if the filter cartridges haven't become separated and you can't find them.
Check "Lab Safety supply" for ideas and the following brands Draeger, North, Scott, MSA.
Draeger makes one I particularly like it is sealed in a can with a pull top lid. It is rated for most chemicals and is NBC rated
Check these manufacturer links;
http://www.msanorthamerica.com/safe_escape_landing_page.html
http://www.draeger.com/ST/internet/...tion/Escape/Filter/DefendAir/pd_defendair.jsp