I've researched this some months ago, but it isn't a one time cost. I arrived at this model: https://www.draeger.com/en_aunz/Applications/Products/Mobile-Gas-D

I've researched this some months ago, but it isn't a one time cost. I arrived at this model: https://www.draeger.com/en_aunz/Applications/Products/Mobile-Gas-Detection/Single-Gas-Detection-Devices/Pac-5500 https://www.draeger.com/en_aunz/Applications/Products/Mobile... But if you want to do it right, you also need a calibration station and calibration gas bottles. It is quite an effort. [No product placement, also look for Honeywell and others.]