Gas R125, also known as pentafluoroethane, is a fluorocarbon with the chemical formula CF3CHF2. It is a colorless, volatile liquid with a mildly sweet taste. It is not flammable, but overexposure can cause dizziness and difficulty concentrating.
Pentafluoroethane is used as a refrigerant and fire extinguishing agent. It has zero ozone depletion potential but a high global warming potential, 3,450 times that of carbon dioxide. It works by absorbing heat as it changes from liquid to vapor during the discharge process, and disrupts the combustion reaction.
The near-azeotropic mixture of pentafluoroethane and difluoromethane, known as R-410A, is a common replacement for various chlorofluorocarbons (commonly known as Freon) in newer refrigerant systems.
Fire extinguishing system
HFC-125 (ECARO-25 / FE-25 / NAF S 125) is a gaseous fire extinguishing agent for use in clean agent fire extinguishing systems. Additionally, HFC-125 leaves no residue on valuable equipment and materials when emitted. It is typically used in situations where water from fire sprinklers would damage expensive equipment, or where water-based firefighting is not feasible, such as in museums, banks, clean rooms and hospitals. HFC-125 cleaners are stored in pressurized containers and introduced into hazardous areas as a gas. The reagent is odorless, colorless, non-conductive, non-corrosive and leaves no residue. It is used in occupied enclosed areas containing high value assets.
HFC-125 suppresses fires by absorbing thermal energy at the molecular level faster than heat can be produced so the fire cannot sustain itself. It also forms free radicals that chemically interfere with the chain reaction of the combustion process. This makes it a highly effective fire extinguishing agent that is safe for personnel and causes no damage to equipment.
HFC-125 is considered a clean agent and is therefore included in the National Fire Protection Association's 2001 - Clean Agent Fire Suppression Systems Standard.
Environmental impact
HFC-125 is measured by the Advanced Global Atmospheric Gas Experiment (AGAGE) at lower atmosphere (tropospheric) stations around the world. Abundances are given as contaminant-free monthly average mole fractions in parts per trillion.
Concentrations of pentafluoroethane in the atmosphere at various latitudes since 2007.
HFC-125 is a non-ozone-depleting alternative to chlorine- or bromine-containing chemicals such as Halon 1301. It is included on the Montreal Protocol's list of controlled substances due to its global warming potential (GWP) of 3,500 times that of CO2 and its atmospheric lifetime of 29 years.
When HFC-125 was introduced to the market, it was not considered safe for use in occupied spaces. EPA's Significant New Alternative Policies (SNAP) list reflects this. With the introduction and acceptance of the PBPK model of the 2004 edition of NFPA Standard 2001 for Clean Agent Fire Suppression Systems, restrictions were relaxed and HFC-125 can now be used in occupied hazardous areas. In general, Class B (flammable liquid) hazards require concentrations that exceed the agent's No Observed Adverse Effect Level (NOAEL), so additional precautions must be taken to avoid prolonged exposure to the agent.
At high temperatures, pentafluoroethane decomposes and produces hydrogen fluoride. The presence of a sharp, pungent odor can be observed, the concentration of which is well below hazardous levels. Other decomposition products include carbonyl fluoride, carbon monoxide and carbon dioxide. The atmosphere should be tested before re-entering a room where the HFC-125 system has been activated to extinguish a fire. Acid-scavenging additives added to pentafluoroethane reduce the amount of hydrogen fluoride.
