jonsi wrote:I don't know much about the topic and I may be way off beam here but here goes...
...powdered aluminium (powdered anything really) can be explosive given the right conditions. To prevent fire you need to take away one element of the fire triangle. Nitrogen inerting systems replace the oxygen in that triangle but only if it is constantly present - like in some aircraft fuel systems. If it were constantly present then the lack of O2 in the atmosphere would be dangerous to humans (asphyxiation risk) because we aren't built to rapidly detect low oxygen atmospheres. If it's designed solely as responsive to fire then it wouldn't react quickly enough to prevent a powder explosion and may even get damaged as a result, rendering it either useless as a fire control or an additional hazard. There's also the safety issue of storage of the liquid nitrogen (temperature / accidental release / pressure vessels etc. etc.).
Not necessarily factors that affect reliability but maybe ones that affect selection?
bernicarey wrote:I think jonsi has about covered it.
Nitrogen inerting is used to prevent explosions by replacing the air (i.e. Oxygen) that is normally present.
It can never really react fact enough to prevent an explosion by use of a reactive system, i.e. like a CO2 or Halon fixed installation that reacts to a fire alarm.
In a powder environment, you have to get the substance in and out of the sealed environment where you have the nitrogen atmosphere.
Aircraft fuel tanks is easy, you just replace the volume of fuel liquid with the gas as the level drops, or purge the tank once empty of fuel, depending on the design requirements. Incidentally, such systems are not that common, even in military aircraft. Certain models of commercial airliners do have such systems, or there is the potential installation of such systems, depending on identified risks.
For many years, aircraft safety has relied on the absence of the ignition source, rather than the removal of the oxygen.
Why we need the sampling points and calibration ? what are the sensor types ?
bernicarey wrote:Why we need the sampling points and calibration ? what are the sensor types ?
Well you will need sampling points to ensure that the Nitrogen levels are at the correct level throughout the controlled atmosphere. There may be atmosphere leakage in or out and levels need to be maintained.
Any sampling would be by a sensor system, and any sensor needs to be calibrated.
I have no idea how such a sensor system would operate. The internet is your friend, here's an example I found...
http://enviro-analytical.com/processins ... h2_n2.html
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