The first way gives a combination of a time-weighted-average concentration over 8hrs (TWA) and a short-term-exposure-limit during 15 min (STEL), from which the values can vary from country to country. The TWA in the Netherlands for example is 0.12 ppm when in France its 1 ppm. The STEL has more or less the same variation. The second way is the MEL, the maximum exposure limit. This is the strictest legislation which states that nobody can be exposed to more than 0.3 ppm formaldehyde at all times. Belgium, Canada and Denmark for example have implemented this legislation. It’s fair to say that the exposure limits to formaldehyde and according legislations have become stricter every year, regardless which method of monitoring (TWA, STEL or MEL) is opposed.