I've been thinking to post on the impact of oxygen depletion and calculation of the oxygen depletion since a while but got delayed due to my hectic schedules.
Have seen some cases of nitrogen bleeding in cleanroom area's and it had led to some catastrophic damages to humans. In my initial stages of career have witnessed a case where a fitter was provided with a job order to fit a filter bag inside ANFD and that guy has applied nitrogen instead of breathing air to his air suit before wearing it, fortunately i had some knowledge on the utility lines, so i've guided him on the lines. Even now in many organizations there wont be color coding's available and some of the operators don't have the awareness on these things.
Anyhow, i've gathered some literature on this and posting them here with some cases.
The cases that i would like to discuss today are,
i. Estimation of oxygen concentration after nitrogen gas leak
ii. Time for depletion of oxygen when ventilation has failed
iii. Time for depletion of oxygen when ventilation is working
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Before going into the calculations deep, lets try to go through the basics.
The major composition of air is Nitrogen and it is almost 78 - 79% and Oxygen constitutes 20 - 21%. Atmosphere containing Oxygen less than 18% is potentially hazardous.
Below is the classification of hazards due to depletion of Oxygen
Let's start our calculation part i.e.,
Case - 1
Estimation of Oxygen concentration after nitrogen gas leak and with failure of ventilation.
Lets use the basic formula here with some minor customizations:
Oxygen concentration = 100 x 20.95% x (Room vol. - Gas leak vol.) / Room vol.
Units are,
Room vol. - m3
Gas leak vol. - m3
If the nitrogen leak is in liquid form i.e., liquid nitrogen, then multiply with 644.
644 is the ratio of liquid nitrogen density to nitrogen gas density = 804/1.25
Now, lets try to take a case study for having better understanding.
The case be, there is a gas leak of 50 m3 in a cleanroom of capacity 800 m3 and the ventilation has failed.
Oxygen concentration = 100 x 0.2095 x (800 - 50)/800 = 19.64%.
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Case - 2
Lets check the second case i.e., Calculation of depletion time after ventilation has failed
Time required = (Room vol./gas leak rate) x (1 - Oxygen concentration/100 x 0.2095)
Time - hours
Room vol. - m3
Nitrogen leakage rate - m3/hr
Oxygen concentration in %
Lets calculate using a case where room vol. is 800 m3, Nitrogen gas leak of 15 m3/hour and Final oxygen concentration of 19%.
Time required = (800/15) x (1 - 19/(100 x 0.2095)) = 53.33 x (1 - 0.90692) = 4.96 hours.
Case - 3
Lets see the last case, where we need to estimate time of oxygen depletion when ventilation is working
Time = (Room vol. x Recirculation %/Gas leak rate) x (0.2095 x 100/Oxygen concentration - 1)
Room vol. - m3
AHU Recirculation in %,
Gas leak rate - m3/hour
Oxygen concentration - %
Now lets check the scenario, where the final oxygen concentration is 19%, room vol. of 800 m3, Gas leak rate of 15 m3/hr and recirculation % (number of air changes) of 50.
Time required = (800 x 0.9 / 15) x ((0.2095 x 100/19) - 1) = 26.666 x 0.1026 = 2.735 hours.
That's it guys......!!!
Hope you have understood the above content, if any queries feel free to write me at pharmacalc823@gmail.com
Comments are most appreciated ....!!!
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Hi! I am Ajay Kumar Kalva, Currently serving as the CEO of this site, a tech geek by passion, and a chemical process engineer by profession, i'm interested in writing articles regarding technology, hacking and pharma technology.
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