crazy people!

[ballisticboy]

No offence committed because no law has been broken.

"By virtue of section 48 of the 1997 Act, firearms using compressed carbon dioxide as the
power source are treated as air weapons and, if not regarded as ‘specially dangerous’
(over 6 foot lbs in the case of a pistol or 12 foot lbs in the case of other air guns and air
rifles) are thus exempt from the firearm certificate procedure. Firearms using other gases
are not so exempt."

The last sentence in the exert from the official Guide on Firearms Licensing above would appear to suggest otherwise. The general opinion is that a FAC is required if you use anything other than air or CO2 which is given special dispensation.

[Terry D]

Nitrogen is inert and makes up about 78% of the air we breathe, nothing wrong in using it at all.....

I couldn't disagree more strongly. The use of nitrogen in PCPs, regardless of its particular properties, would represent a departure from the safe, easy-to-understand rule of 'diver's quality air only', and that is a potentially disasterous departure. When we step away from the safest system through experimentation with gasses other than air, the potential for life-changing injury or death outweighs any percieved gains. I say this after personally witnessing the aftermath of PCPs filled with oxygen and oxy-acetylene, and the injuries this caused. Make no mistake, if we ever sanction the use of gasses other than air, sooner or later someone will be seriously injured or killed.

[sevorg]

Nitrogen at higher percentages will suffocate you. This is what happens to people at altitude where the air is described as thin due to the lower percentage of oxygen and higher percentage of nitrogen. Nitrogen is used in tyres due to it being more temperature stable. It has a much lower expansion rate than air as it is heated.

Is the ratio of nitrogen to oxygen different at altitude? I thought the problem at high altitude was simply less oxygen (and less nitrogen) due to less air in a given volume (lower density)

[Rob Edge]

"By virtue of section 48 of the 1997 Act, firearms using compressed carbon dioxide as the
power source are treated as air weapons and, if not regarded as ‘specially dangerous’
(over 6 foot lbs in the case of a pistol or 12 foot lbs in the case of other air guns and air
rifles) are thus exempt from the firearm certificate procedure. Firearms using other gases
are not so exempt."

The last sentence in the exert from the official Guide on Firearms Licensing above would appear to suggest otherwise. The general opinion is that a FAC is required if you use anything other than air or CO2 which is given special dispensation.

Wrong. CO2 used to be on certificate so that bit of law simply moved them into the category of air guns without FAC requirement unless suitably dangerous, ie over 12ftlb/6ftlb

[Rob Edge]

Is the ratio of nitrogen to oxygen different at altitude? I thought the problem at high altitude was simply less oxygen (and less nitrogen) due to less air in a given volume (lower density)

Try here https://www.higherpeak.com/altitudechart.html

[Shed tuner]

Try here https://www.higherpeak.com/altitudechart.html

Rob, your link says that Sevorg is correct:
"Use the tables below to see how the effective amount of oxygen in the air varies at different altitudes. Although air contains 20.9% oxygen at all altitudes, lower air pressure at high altitude makes it feel like there is a lower percentage of oxygen. "

The key word being "effective" oxygen levels, not actual percentages

[Scubashot]

Is the ratio of nitrogen to oxygen different at altitude? I thought the problem at high altitude was simply less oxygen (and less nitrogen) due to less air in a given volume (lower density)

The ratio remains the same but the problem arises due to the physics of partial pressures.
At 1 atmosphere there is roughly a partial pressure of 0.21 of oxygen and 0.79 of nitrogen.
At 2 atmospheres (eg 10 metres under water on scuba. 1 ATM of water pressure and the original 1 of air pressure) there is a partial pressure of oxygen of 0.42 and a partial pressure of nitrogen of 1.58.
Conversely at 0.5 atmospheres at altitude the partial pressure drops to 0.105 of oxygen and 0.395 of nitrogen.

The important thing is how the human body reacts to the partial pressures of these gasses. From memory a partial pressure of less than 0.16 of oxygen will result in a loss of consciousness and less than 0.12 may be fatal.
In diving we have to consider that both oxygen toxicity and nitrogen narcosis will occur as the levels rise,. This will result in convulsions and potential drowning from oxygen and irrational behaviour and potential drowning from nitrogen.
To combat these effects we accurately blend gasses to provide the correct partial pressures for the required depth of dive and will switch between different mixes on the descent and ascent.
It may be further complicated by wishing to increase the oxygen content of our decompression gasses to accelerate the process!

Stick to air in your guns, it's far less complicated! :-)

[ballisticboy]

Wrong. CO2 used to be on certificate so that bit of law simply moved them into the category of air guns without FAC requirement unless suitably dangerous, ie over 12ftlb/6ftlb

I think that is what it says, CO2 is changed to being considered in the same category as an airgun but no other gasses are given the same dispensation. I do not understand why you are saying it is wrong since it is quite clear.

[Turnup]

Nitrogen at higher percentages will suffocate you. This is what happens to people at altitude where the air is described as thin due to the lower percentage of oxygen and higher percentage of nitrogen. Nitrogen is used in tyres due to it being more temperature stable. It has a much lower expansion rate than air as it is heated.

Not so. The coefficient of expansion of all gasses is the same provided that the gas is not at a pressure or temperature close to a phase change (condense, evaporate, or solidify). This is easily verified using google.

There is some controversy over the use of Nitrogen in tyres and I have not been able to find any satisfactory explanation other than for tyres used in extreme conditions. Aircraft tyres run at typically 200 psi and at that pressure oxygen becomes much more reactive - this might also be the case for truck tyres. For car tyres = snake oil.

Racing car tyres run at very low pressures and I have been unable to understand why they use N - even the thermal conductivity of N and air are very nearly the same. It may be that they have always done it this way.

[krisko]

If you have a 15L 300bar cylinder it will have 300x15=4500Liters of air in it (or Nitrogen be it)

a very small room of for example 3mx2mx2ms will have 12000 liters of Air in it. You see the difference in numbers? It gives you the idea.


Even if you dump a full cylinder of Nitrogen into it, will still not kill you. Nitrogen will displace the oxygen yes, if you travel in lift with liquid nitrogen container that is not safe really
But normal room size is OK. You get it.

i can recommend Nitrogen, very dry. lolIt still escapes me why people mess around with compressors these days.

[Scubashot]

If you have a 15L 300bar cylinder it will have 300x15=4500Liters of air in it (or Nitrogen be it)

a very small room of for example 3mx2mx2ms will have 12000 liters of Air in it. You see the difference in numbers? It gives you the idea.


Even if you dump a full cylinder of Nitrogen into it, will still not kill you. Nitrogen will displace the oxygen yes, if you travel in lift with liquid nitrogen container that is not safe really
But normal room size is OK. You get it.

i can recommend Nitrogen, very dry. lolIt still escapes me why people mess around with compressors these days.

As far as I am aware the largest available 300 bar scuba cylinder is only 12 litres, which does still contain more gas than a 232 bar, 15 litre cylinder.

I am not sure how compressed nitrogen gas is produced commercially but I would imagine that compressors are involved at some point.
We certainly use molecular filters with some dive compressors to reduce the nitrogen content of our breathing gas. It is an alternative method of producing enriched air (nitrox), rather than putting a specified pressure of pure oxygen into a tank before topping off to the required pressure with air.

As long as appropriate water filters are incorporated into the compressor then air is certainly dry enough for use in any air gun. It is also widely and cheaply available from many different outlets.

[DedIdick]

As far as I am aware the largest available 300 bar scuba cylinder is only 12 litres, which does still contain more gas than a 232 bar, 15 litre cylinder.

I am not sure how compressed nitrogen gas is produced commercially but I would imagine that compressors are involved at some point.
We certainly use molecular filters with some dive compressors to reduce the nitrogen content of our breathing gas. It is an alternative method of producing enriched air (nitrox), rather than putting a specified pressure of pure oxygen into a tank before topping off to the required pressure with air.

As long as appropriate water filters are incorporated into the compressor then air is certainly dry enough for use in any air gun. It is also widely and cheaply available from many different outlets.

Air through a Molecular sieve and recip compressors to get whatever pressure you're wanting.

http://www.nitrogen-generators.com/n...-how-it-works/

[Scubashot]

Air through a Molecular sieve and recip compressors to get whatever pressure you're wanting.

Yes, I suspected as much, so it looks like people will continue to "mess around with compressors" whether to compress air or extract the nitrogen and compress that!

[robinghewitt]

If I ever want to off myself then it's nitrogen for me. The thing that makes the nitrogen leak so dangerous is that you don't realise you are dying. It is like turning off the oxygen on a rebreather, you just fade away. This was demonstrated on TV by Jonathan Miller, in the days before political correctness, so we would all know how to off ourselves painlessly. Be sure to leave a note on the door.

I use it for the plasma cutter because it is dry, something that plasma cutters really seem to appreciate for some reason known only to plasma cutters and plasma cutter geeks. Perhaps air guns would also prefer dry? It is also very cheap

[Scubashot]

If I ever want to off myself then it's nitrogen for me. The thing that makes the nitrogen leak so dangerous is that you don't realise you are dying. It is like turning off the oxygen on a rebreather, you just fade away. This was demonstrated on TV by Jonathan Miller, in the days before political correctness, so we would all know how to off ourselves painlessly. Be sure to leave a note on the door.

I use it for the plasma cutter because it is dry, something that plasma cutters really seem to appreciate for some reason known only to plasma cutters and plasma cutter geeks. Perhaps air guns would also prefer dry? It is also very cheap

I guess the "dryness" is a feature of the molecular sieve removing the H2O molecules as well as the O2 etc. Certainly dry air is preferable for anything mechanical and metal working at fine tolerances, like scuba regulators and PCP airguns.
Even well maintained diving compressors leave the air dry enough to cause students to complain of dry mouths and dehydration induced cramps as they inhale dry air and exhale moist.
Funnily enough, that is another of the advantages of rebreathers: you get to inhale warm moist air as a by-product of the chemical reaction of the CO2 scrubber unit.