Hi @ all,<br>does anybody know the formula to calculate the time remaining for one or more persons to breath (oxygen) in a closed room???<br><br>Thank's for reading and greetings to all,<br><br>J. Mueller (Hamburg, Germany)

It's not exact science. Each individual will remain conscious at different levels of hypoxia (lack of O2 in the blood) The range is narrow. The variables are these. Cubic volume of air (room size hieght X Length X width) air Oxygen concentration (21% is normal) O2 exchange rate for individuals involved - here is where it get difficult. activity level, size, muscle mass% stress level, general health all affect the rate at which an individual will convert O2 to CO2. In a normal healthy individual without breathing problems the 21% O2 concentration in becomes somewhere near 14% O2 concentration out. This 14% concentration is still sufficient to revive someone through Mouth to Mouth resucitation. I would expect that O2 concentrations below 8% might begin to be a serious problem. Don't know the exact level. As O2 concentrations become lower the other gasses become important. If there is any CO (carbon Monoxide) in the room the blood will bind it preferentially over O2 so you could suffocate in a rather high O2 concentration if there is also a high concentration of CO. There is also a reflex that kicks in for some during hypoxia and hypothermia called the dive responce. When this happens the individuals use of O2 is drastically reduced and they may survive for a much longer time. It has been reported that some Yogi's (practitioners of Yoga) can reduce their breathing rate to very low levels thus reducing thier usage of O2 drastically. Though the Yogi's may be exchanging O2 more efficiently and exhaling a lower concentration of O2 than a person breathing normally.<br><br>BeachDoc, is there any lower threshold of O2 concentration in otherwise normal air mix that would be considered deadly? (O2 replaced with CO2, no other change in the normal gas mix in air.)

Oxygen Concentration<br> Symptoms<br> <br>21 %<br> None (normal oxygen level)<br> <br>15 %<br> No immediate effects<br> <br>14 %<br> Fatigue, impaired judgement<br> <br>10 %<br> Dizziness, shortness of breath, deeper and more rapid breathing<br> <br>7 %<br> Stupor sets in<br> <br>5 %<br> Minimum amount that will support life<br> <br>2 % - 3 %<br> Death within 1 minute<br> <br><br>Search the web for CONFINED SPACE OXYGEN CONCENTRATION. There is a lot of information about how much O2 is needed to sustain life. The time it takes to die is dependent on a number of factors including the rate at which oxygen is depleted, if other gases are in the area that have negative effects, other hazards, etc. Basically you want to keep the O2 between 19% and 23%. Lower than that you start having problems. Higher than that and you get into highly explosive environments.

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