Carbon dioxide has been used in fire fighting for over 50 years. It is generally specified in locations where people will not be working since it is hazardous to humans in the concentrations deployed by fire suppression systems. Since there are no chemical residues left after use, CO2 systems are suitable for food industries and other situations where contamination is to be avoided. A further advantage is the low cost of refilling the storage cylinders.
At atmospheric pressures carbon dioxide is a colourless, odourless and non-conductive gas capable of quickly and efficiently penetrating the area to be protected. Its density is approximately 50% greater than the density of air so it quickly forms a smothering blanket on the fire. CO2 is stored in high-pressure cylinders as liquefied gas.
CO2 has been used effectively for many years, not only in fire protection but also in other commercial applications. Although the use of CO2 as an extinguishing agent declined with the introduction of halons, the Montreal Protocol (which requires the reduction in use of ozone-depleting substances) has ensured it continues to be a popular solution for fire protection.
CO2 physically extinguishes fires in two ways. Firstly it decreases the oxygen level in the enclosure from 21% to below 15%, meaning that most fires are unable to continue combusting. Secondly the gas absorbs heat and cools the fire down.
When dealing with the protection of occupied areas consideration should be given to the fact that if CO2 is inhaled, even at low concentrations, it may lead to asphyxia. Under required safety precautions, CO2 has been effectively applied for over 50 years to protect areas such as transformer rooms, archives, electrical hazards, record stores and computer rooms.