Is the carbon dioxide in compressed gas systems dangerous ?
500 g of carbon dioxide are equivalent to 11.36 mol (1 mol of carbon dioxide weighs 44.01 g).
1 mol of an ideal gas occupies 22.4 l volume under normal conditions (normal air pressure and temperature), which means the following for 500 g of carbon dioxide:
11.36 x 22.4 l = 254.48 l.
A room of 20 m2 (4 m x 5 m) and a ceiling height of 2.5 m contains 50 m³ of air, which is 50,000 l.
Carbon dioxide is heavier than air and collects at the bottom under calm conditions. The gas would be 1.27 cm above the ground with 500 g of carbon dioxide.
Then, correspondingly, 4 times higher with 2 kg.
When the CO₂ is mixed with the air in the room, 254.48 l of carbon dioxide correspond to a concentration of 0.5 % of carbon dioxide with 50,000 l room volume of a room with a size of 20 m2 and a standard ceiling height, which is in the range of the maximum work place concentration for an 8-hour working day.
Accordingly, no excessive danger is associated with carbon dioxide compressed gas systems for aquariums.
Nevertheless, a few points should be observed when dealing with a compressed gas system:
1) Please be aware that the compressed gas cylinders must undergo a TÜV test regularly every 10 years.
2) Rusty cylinders, especially with rust near or on the bottom, should no longer be used, even if they have a valid TÜV mark.
3) Do not store the compressed gas cylinders in the sun, as this causes the internal pressure to rise. Normally, nothing will happen if you do, as the cylinders are constructed to withstand pressures up to 200 bar, but the bursting disk may burst, thereby causing all the gas to escape. In this case, do not touch the cylinder without hand protection, as the cylinder becomes very cold due to the drop in pressure.