If you are using an air purifying respirator with filter cartridges for ammonia, make sure you use the ammonia cartriedges. Ammonia cartridges are exclusively for ammonia (and Methylamine) only. Do not use ammonia cartridges for other types of gases or vapors. Worldwide (international) color code for ammonia cartridges is green. If your worker cannot read the label, make sure they choose the green cartridge. If you see white cartridges fitted on their respirator (for ammonia), you kown immediately that it is wrong.
Want to know more about the color code for different types of cartridges? American standard uses black is for oganic vapors, white is for acid gases including chlorine, yellow is for organic vapors + acid gases, grey for multigas. European (EN) uses different color codes. Both use green for ammonia.