Inergen
Inergen is the brand name for a patented mixture of nitrogen , argon and carbon dioxide that is used as an extinguishing agent for fire fighting . The name is an artificial word that is made up of the English terms “ inert gas” (argon) and “nitro gen ” (nitrogen).
If the oxygen content in the room air is reduced by extinguishing it with Inergen , the oxygen uptake through human breathing is largely retained.
Inergen consists of 52 percent by volume (vol .-%) of nitrogen, 40 vol .-% of argon and 8 vol .-% of carbon dioxide. All of these gases are odorless, tasteless and non-flammable. Carbon dioxide splits at only about 2000 ° C in oxygen and carbon monoxide on.
The composition results in a density at which Inergen only slowly escapes from relatively tightly sealed rooms. In this way, the extinguishing gas concentration can be maintained over a long period of time. According to the extinguishing principle, it is only used in stationary systems, not in hand-held fire extinguishers or the like.
Inergen is stored in bottles with 200 or 300 bar . The partial pressure of CO 2 is at most (0.08 ⋅ 300 bar =) 24 bar, so that no liquefaction (57 bar vapor pressure) takes place at room temperature. In the absence of a phase transition, relaxation does not cool down as much as with liquid CO 2, and this means that visibility is not as severe as the result of condensation of water mist. For Inergen, 1.65 to 2.2 liters of (bottle) storage volume must be provided for each cubic meter of room volume.
Human compatibility
The physiological effect of carbon dioxide (CO 2 ) is important for the human tolerance of Inergen . When there is a lack of oxygen, it accelerates breathing so that people in the room can continue to breathe.
The human body is constantly producing CO 2 . The body tries to keep the pressure in the blood constant (around 40 Torr ) so that it does not become overly acidic ( acidosis ) or too little acidity ( alkalosis ). The brain notices any change in CO 2 concentration and stimulates the lungs to either exhale more CO 2 or to hold back. If there is less oxygen in the circulating air than normal, breathing would have to be increased in order to keep the body functional. But the opposite is the case, as more CO 2 would have to be released through increased breathing than can be taken up again. However , if there is now a CO 2 concentration in the air that can compensate for this, breathing is increased. The acidity is kept constant and the blood flow to the brain does not decrease. The CO 2 concentration in a room must not exceed 5% by volume.
If only Inergen is used instead of inert gases , the oxygen concentration can be reduced to 14 to even 10% by volume, without this leading to death.
If Inergen (which itself contains 8% CO 2 ) is added to air in a ratio of 50:50 , this mixture still contains a good 10% oxygen and 4% CO 2 , which significantly dampens combustion processes and (forced) breathing is barely life-sustaining for people lets be. Halving the oxygen content in the same way with argon would not accelerate breathing; halving it with CO 2 alone causes people to suffocate from an excessively high CO 2 content of 50%.