Victoria Britten (asker) Sep 9, 2013:

Context: sentence Natural gas, Pit gas, Liquefied gas such as propane,LNG, wellhead gas (petroleum gas); all gases in which the
concentration of every single pollutant gas component does not exceed 20% of the permissible limit value;

kashew Sep 9, 2013:

More context would be very helpful, V.

Renate Radziwill-Rall Sep 9, 2013:

Christine was soll das?

kashew Sep 9, 2013:

Grisou translated that way in:
Fresh air was not only needed by the miners underground, it was also necessary to reduce the levels of explosive ***pit gas**.
erih.net

Le travail souterrain demeurait extrêmement dangereux et très nocif pour la santé : en raison du risque permanent d'une explosion ou d'un coup de ***grisou***, en raison des effondrements et du travail harassant.
erih.net
Although usually grisou = firedamp.