Halons ozone depletion potentials

While the tropospheric concentrations of CFCs and halons are not increasing as rapidly in the past due to controls outlined in the Montreal Protocol and subsequent amendments, those of the CFC replacements are increasing. However, due to their different structures and reactivities, the ozone depletion potentials associated with these compounds are significantly less that those of the compounds they replace. This truly represents a success story in terms of application of atmospheric chemistry to the development of effective control strategies. 

TABLE 2. Atmospheric lifetime, ozone depletion potential (ODP) and global warming potential (GWP) of CFCs, HCFCs, HFCs and halons... 

Stratospheric ozone Emission of ozone-depleting compounds (CFCs, Halons) Chemical reaction release of C1 and Br in stratosphere Catalytic destruction of ozone in stratosphere Skin and crop damage, damage to materials Ozone Depletion Potential (ODP)... 

One example of this type of product innovation is the 3M Novec 1230 Fire Protection Fluid that was developed using a balanced lifecycle approach. Until the early 1990s, halon was used for critical fire protection applications (e.g., communications and electronic equipment). With the production of halons banned because of high ozone depletion potential and most of the halon replacement... 

CFCs reference is made to the ozone-depleting potential of CFCs and halons, and Neste s planned replacement of these compounds. During 1998 the quantity of these compounds in use increased from 25 tons to 27 tons ... 

Until now the main application of trifluoromethyl bromide was its use as Halon 1301 in aeronautic ( ref. 13).Unfortunatly, Halons are implicated in the depletion of stratospheric ozone. The participants of the 1992 Montreal Protocol Meeting in Copenhagen agreed to phase out Halon production by the year 1994, except for some essential fire-fighting uses. Research on alternative agents have been initiated in order to find new products with low or zero Ozone Depletion Potential. However, the numerous candidates examined so far present... 

Figure 3. World consumption of CFCs and Halons by major application in 1986 as weighted value of ozone depletion potential (ESCAP, 1995).

The presence of bromine atoms and longer atmospheric lifetime of halons make them highly potent stratospheric ozone depleting agents. For instance, the ozone depletion potential (ODP) of halon 1301 is estimated to be 10 with respect to that of CCl F (CFC-11) taken as 1. The ODP values for halon 2402 and halon 1211 are 6 and 3, respectively. The global warming potentials (GWP over 100 year time horizon, relative to CO =1) of halon 1211, halon 1301 and halon 2402 are estimated as 1890, 7140 and 1640, respectively. 

HCFCs are allowed as stop-gap replacement for halons and CFCs. Ultimately, they will also be phased out of production due to their GWP and small OOP. Halocarbon gas systems are formd to be more convenient in suppressing fires in place of halons. A number of fire extinguishing halocarbon gases with zero ozone depletion potential (ODP) have been developed. These include both HFCs such as pentafluoroethane, 2H-heptafluoropropane and... 

In this sequence the Cl also acts as a catalyst and two molecules are destroyed. It is estimated that before the Cl is finally removed from the atmosphere in 1—2 yr by precipitation, each Cl atom will have destroyed approximately 100,000 molecules (60). The estimated O -depletion potential of some common CFCs, hydrofluorocarbons, HFCs, and hydrochlorofluorocarbons, HCFCs, are presented in Table 10. The O -depletion potential is defined as the ratio of the emission rate of a compound required to produce a steady-state depletion of 1% to the amount of CFC-11 required to produce the 1% depletion. The halons, bromochlorofluorocarbons or bromofluorocarbons that are widely used in fire extinguishers, are also ozone-depleting compounds. Although halon emissions, and thus the atmospheric concentrations, are much lower than the most common CFCs, halons are of concern because they are from three to ten times more destmctive to O, than the CFCs. 

Oxidizer Chemical substance that causes oxygen to combine with another chemical substance examples include oxygen and hydrogen peroxide Ozone depletion Destruction of the stratospheric ozone layer that protects the Earth from harmful effects of ultraviolet radiation. Depletion of ozone layer is due to the breakdown of certain chlorine- and/or bromine-containing compounds (chlorofluorocarbons or halons), which break down when they reach the stratosphere and then catalytically destroy ozone molecules Ozone layer Protective layer in the atmosphere, about 15 miles above the ground. The ozone layer absorbs some of the sun s ultraviolet rays, thereby reducing the amount of potentially harmful radiation that reaches the Earth s surface PAHs Polycyclic aromatic hydrocarbons... 

Under the agreements of the Montreal Protocol on Substances that Deplete the Ozone Layer, the production of chlorofluorocarbons (CFCs), halons and several other halocarbons has been prohibited [1,2]. Consequently, there is an interest in replacing these compounds [3]. As part of the development of such replacing compounds, it is necessary to consider and evaluate the potential environmental effects of their use, especially on stratospheric ozone [2],... 

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