If you miss the chance mentioned in busterfrosty's guide, you can get it out in the open world. If you wear your gasmask in combat, it'll begin to take damage. Eventually, you will see a hole in the glass in the bottom left corner. DO NOT take it to a workbench to fix, instead, wear it in an area that is toxic and requires the mask. You'll be given a prompt to fix the mask. Artyom will place a square of tape over the hole. Once the animation is complete the achievement will unlock.