Carbon dioxide, toxic effects

Carbon dioxide fire extinguishers are widely used in laboratory fire fighting because the C02 does not damage apparatus or cause electrical shorts. Furthermore, carbon dioxide is effective against a wide variety of fires and is not toxic. The National Fire Protection Association adopts the following classification of fires ... 

Butylenes are not toxic. The effect of long-term exposure is not known, hence, they should be handled with care. Reference 96 Hsts air and water pollution factors and biological effects. They are volatile and asphyxiants. Care should be taken to avoid spills because they are extremely flammable. Physical handling requires adequate ventilation to prevent high concentrations of butylenes in the air. Explosive limits in air are 1.6 to 9.7% of butylenes. Their flash points range from —80 to —73° C. Their autoignition is around 324 to 465°C (Table 2). Water and carbon dioxide extinguishers can be used in case of fire. 

In the process of burning, toxic compds are formed, which may produce delayed effects on personnel exposed to the smoke (Ref 7, p 101) Triethylaluminum (TEA). A number of organo-metallic compds are spontaneously inflammable in air. Others, like organosodium and organo-potassium compds, are not only spontaneously inflammable in air but react violently with w and carbon dioxide (Ref 4, p 24)... 

It has been shown that carbon dioxide also increases the toxicity of the other gases currently included in the model. For example, the 30 minute plus 24 hour LC50 value of HCN decreases to 75 ppm and that of 02 increases to 6.6% in the presence of 5% C02. However, we empirically found that the effect of the C02 can only be added into this equation once. At this time, we have data on the effect of various concentrations of C02 on CO and only have information on the effect of 5% C02 on the other gases. Since CO is the toxicant most likely to be present in all real fires, we have included the C02 effect into the CO factor. As more information becomes available, the N-Gas equation will be changed to indicate the effect of C02 on the other gases as well. 

A number of studies have been made of combinations of individual toxic gases. Most of these studies show that the effects of these combinations of toxic gases are simply additive. This has been found empirically for CO and HC1 [52] and for CO and HCN [44], although the mechanisms of action are different. These results can be interpreted as each toxicant taking its toll and acting on a weakened system. The CO-carbon dioxide combination has been claimed to be synergistic [53]. 

Ibrahim et al. 1963). Aiken and Braitman (1989) determined that cyanide has a direct effect on neurons not mediated by its inhibition of metabolism. Consistent with the view that cyanide toxicity is due to the inability of tissue to utilize oxygen is a report that in cyanide-intoxicated rats, arterial p02 levels rose, while carbon dioxide levels fell (Brierley et al. 1976). The authors suggested that the low levels of carbon dioxide may have led to vasoconstriction and reduction in brain blood flow therefore, brain damage may have been due to both histotoxic and anoxic effects. Partial remyelination after cessation of exposure has been reported, but it is apparent that this process, unlike that in the peripheral nervous system, is slow and incomplete (Hirano et al. 1968). The topographic selectivity of cyanide-induced encephalopathy may be related to the depth of acute intoxication and distribution of blood flow, which may result in selected regions of vascular insufficiency (Levine 1969). 

An enzyme is a protein that speeds up a biochemical reaction without itself experiencing any overall change. In chemical language, such a compound is called a catalyst and is said to catalyze a reaction. Chemists employ a variety of compounds as laboratory catalysts, and many industrial chemical processes would be impracticably slow without catalysis. An automobile s catalytic converter makes use of a metal catalyst to accelerate conversion of toxic carbon monoxide in the exhaust to carbon dioxide. Similarly, our bodies biochemical machinery effects thousands of different reactions that would not proceed without enzymatic catalysis. Some enzymes are exquisitely specific, catalyzing only one particular reaction of a single compound. Many others have much less exacting requirements and consequently exhibit broader effects. Specific or nonspecific, enzymes can make reactions go many millions of times faster than they would without catalysis. 

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