Hi all,<br><br>thank's miniME and Resqman!<br><br>In according to your answers respectively infos I've developped the following formula(s):<br><br><br>t_max. [in minutes]:<br><br>cubic volume of room size [in litres] * 2<br>--------------------------------------<br>number of persons * 20<br><br><br>t_min. [in minutes]:<br><br>cubic volume of room size [in litres] * 2<br>--------------------------------------<br>number of persons * 120<br><br><br>'Cubic volume of room size * 2' because I've thought that every single litre of air could be breathed two times before reaching a critical level of oxygen concentration.<br><br>'Number of persons * 20' resp. '* 120' cause a person resting will have a consumption of 20 l air per minute, a person under working conditions will breath 120 l.<br><br>What do u think? Good attempt or scrap???<br><br>Sir Vivor