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taydin
09-22-2010, 05:39 AM
I have a planted aquarium and I am injecting CO2 to the tank using a 2Kg CO2 bottle. I bought the bottle from a fire extinguisher vendor.

There is a regulator at the output of the bottle. The input pressure is 70 bar and the output pressure is 2 bar. The regulator has a high precision valve which allows the gas flow to be adjusted to a very little amount. I am measuring the gas flow rate by counting the number of bubbles in the water. Currently it is like 2 bubbles per second.

Everything is normal so far. But my concern is, if for some reason the CO2 gas starts leaking into the house, would the 2Kg CO2 be fatal? I have an air inlet in the kitchen and there are outlets in both bathrooms. So there is a constant and slow air circulation throughout the year. So a slow leak probably wouldn't be an issue. But what if all the CO2 would be suddenly released? Any opinions appreciated :)

macona
09-22-2010, 05:58 AM
I also used CO2 in my tank, but for a calcium reactor for my salt water setup.

CO2 is 8.741 cuft in gas per pound liquid. Say 2kg is about 4 lbs so figure about 35cu ft in a tank. Thats not much really. It would have to be in a really small room to be a worry. Even a really small room may be 1000 cubic feet so dumping that all at once would only increase the CO2 by ~3.5%. CO2 becomes toxic at 5% (So google says). And thats if you dumped a freshly filled bottle.

Weston Bye
09-22-2010, 05:59 AM
The question is, how much of the oxygen in the house would be displaced by a sudden release of the CO2? Any gas, toxic or inert, that reduced the oxygen content below survivable levels could be fatal.

CO2 is not toxic in the same way that carbon monoxide (CO) is - you exhale CO2 with every breath. But too much of it, rather than oxygen isn't good.

The tank has 2kg by weight of the gas at 70 bar. How many liters or cubic centimeters does that translate to at 1 bar. You could measure the volume of the tank and multiply by 70 for a rough idea of the volume of gas that it would release into the house.

An oxygen level monitor could be helpful, but don't depend on it.

taydin
09-22-2010, 06:24 AM
Thanks for the responses! I feel much better now :)

The likelihood of the bottle developing such a sudden leak is very low, but it is good to know that even if the worst case happens, it won't be an issue.

The bottle is about 50cm tall and 15cm in diameter. Let's assume the bottle is cylindrical. Then volume will be 2300cm3. That is about 0.23m3. Multiply that by 70 gives 16m3.

The apartment is 110m2 and the ceilings are 2.6m high. So the total volume is 286m3.

This gives a ratio of 16 / 286 = 5.5%

However, because of the high pressure, the walls of this bottle are very tick. And also, it isn't cylindrical. So adjusting for that, I would think the volume is probably half of 0.23. In that case, the ratio would be 2.75, which is below the threshold that macona gave.

Arcane
09-22-2010, 06:48 AM
A quick Google search also gives this...

"Question - How much oxygen is needed to remain in the air
before a person goes unconscious?
---------------------------------------
This would vary greatly depending upon the condition of the person.

The following site offers an approximation:

http://ehs.ucdavis.edu/hs/ConfSpace/index.cfm

* 20.9-23.5 percent: Maximum permissible oxygen level. No effect.
* 20.9 percent: Percentage of oxygen found in normal air. No effect.
* 19.5 percent: Minimum permissible oxygen level. No effect.
* 15-19 percent: Decreased ability to work strenuously. May
impair coordination and may induce early symptoms with individuals
that have coronary, pulmonary, or circulatory problems.
* 12-15 percent: Respiration and pulse increase; impaired
coordination, perception, and judgment occurs.
* 10-12 percent: Respiration further increases in rate and depth;
poor judgment and bluish lips occur.
* 8-10 percent: Symptoms include mental failure, fainting,
unconsciousness, an ash-colored-face, blue lips, nausea, and vomiting.
* 6-8 percent: 8 minutes - 100 percent fatal; 6 minutes - 50
percent fatal; 4-5 minutes - recovery with treatment.
* 4-6 percent: Coma in 40 seconds, convulsions, respiration
ceases - death."

As macona says, CO2 becomes toxic at 5%, so the percentage of O2 isn't the only parameter you have to think about. The density of carbon dioxide is about 1.5 times that of air so if the leak occurred when there was least air movement (as it might be if you were sleeping and between furnace or AC cycles) the closer to the floor you got, the higher the CO2 concentration would be. You might not have anything to worry about at head height in a bed but I wouldn't want to bet the family pets that sleep on the floor would be ok.

Evan
09-22-2010, 06:49 AM
There is a very big difference between CO and CO2, especially in how the body responds to it. While both are odorless CO2 has a very pronounced and easily recognized effect if it is present in significant amounts. If there is too much CO2 in the air you will immediately feel short of breath and begin to breath much faster. This happens long before the amount reaches toxic proportions. And yes, CO2 is toxic in large amounts, it doesn't just displace oxygen. Too much CO2 will cause disregulation of the mechanism that tells the body to breath. Even if the body has enough oxygen too much CO2 will cause CO2 narcosis as well as systemic acidosis.

added: Note that acidosis can cause convulsions and heart failure.

camdigger
09-22-2010, 06:50 AM
FWIW, one of my handbooks quotes 543.7 sm3 gas per m3 liquid at -18C and 2070 kPa.

Evan
09-22-2010, 06:54 AM
"Question - How much oxygen is needed to remain in the air
before a person goes unconscious?


Note that the absolute amount of oxygen in the air is not what those numbers represent. They represent the partial pressure of oxygen compared to other gases. At 12000 feet the amount of oxygen in the air is half what it is at sea level but the proportion of oxgen in the air remains the same up to about 50,000 feet. We can live just fine on half the normal amount of oxygen as long as it remains in the same proportions with the other gases.

taydin
09-22-2010, 08:38 AM
Yes, according to the information I read, high CO2 concentration is easily noticable by humans. But, is it still noticeable while sleeping? For example, if the rate of breathing or the heart rate goes up, would you wake up?

Evan
09-22-2010, 09:24 AM
You will wake up rather than die sleeping. It is the same as what happens during sleep apnea. The symptom of too much CO2 in your blood is the same as holding your breath, which is effectively the same as sleep apnea. The cardinal feature of sleep apnea is waking even from deep sleep many times per night.

dp
09-22-2010, 09:54 AM
The cardinal feature of sleep apnea is waking even from deep sleep many times per night.

In my case I wake many times to adjust my face mask. And the other feature is bizarre dreams.