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The amount of material present and its concentration must be considered along with physical and chemical properties to determine the magnitude of the hazard. Hydrogen peroxide, for example, is used as an antiseptic and a hair bleach in low concentrations (approximately 8 percent in water solution). Over 8 percent, hydrogen peroxide is classed as an oxidizer and is toxic. Above 90 percent, it is a Class 4 oxidizer "that can undergo an explosive reaction when catalyzed or exposed to heat, shock or friction," a definition which incidentally also places hydrogen peroxide over 90-percent concentration in the unstable (reactive) category. Small amounts at high concentrations may present a greater hazard than large amounts at low concentrations.
E103.1.3.1 Mixtures
Gases—toxic and highly toxic gases include those gases which have an LC50 of 2,000 parts per million (ppm) or less when rats are exposed for a period of 1 hour or less. To maintain consistency with the definitions for these materials, exposure data for periods other than 1 hour must be normalized to 1 hour. To classify mixtures of compressed gases that contain one or more toxic or highly toxic components, the LC50 of the mixture must be determined. Mixtures that contain only two components are binary mixtures. Those that contain more than two components are multi-component mixtures. When two or more hazardous substances (components) having an LC50 below 2,000 ppm are present in a mixture, their combined effect, rather than that of the individual substances (components), must be considered. In the absence of information to the contrary, the effects of the hazards present must be considered as additive. Exceptions to the above rule may be made when there is a good reason to believe that the principal effects of the different harmful substances (components) are not additive.

For binary mixtures where the hazardous component is diluted with a nontoxic gas such as an inert gas, the LC50 of the mixture is estimated by use of the following formula:



(Equation E-1)

For multi-component mixtures where more than one component has a listed LC50, the LC50 of the mixture is estimated by use of the following formula:



(Equation E-2)

where:

LC50m   = LC50 of the mixture in parts per million (ppm).
 
Ci = concentration of component (i) in decimal percent. The concentration of the individual components in a mixture of gases is to be expressed in terms of percent by volume.
 
LC50i = LC50 of component (i). The LC50 of the component is based on a 1-hour exposure. LC50 data which are for other than 1-hour exposures shall be normalized to 1-hour by multiplying the LC50 for the time determined by the factor indicated in Table E103.1.3.1. The preferred mammalian species for LC50 data is the rat, as specified in the definitions of toxic and highly toxic in Chapter 2 of the Fire Code of New York State. If data for rats are unavailable, and in the absence of information to the contrary, data for other species may be utilized. The data shall be taken in the following order of preference: rat, mouse, rabbit, guinea pig, cat, dog, monkey.
 
in = component 1, component 2 and so on to the nth component.

Examples:
  1. What is the LC50 of a mixture of 15-percent chlorine, 85-percent nitrogen?

    The 1-hour (rat) LC50 of pure chlorine is 293 ppm.

    LC
    50m = 1 / (0.15 / 293) or 1,953 ppm. Therefore, the mixture is toxic.
  2. What is the LC50 of a mixture of 15-percent chlorine, 15-percent fluorine and 70-percent nitrogen? The 1-hour (rat) LC50 of chlorine is 293 ppm. The 1-hour (rat) LC50 of fluorine is 185 ppm.

    LC
    50m = 1 / (0.15 / 293) + (0.15 / 185) or 755 ppm. Therefore the mixture is toxic.
  3. Is the mixture of 1 percent phosphine in argon toxic or highly toxic? The 1-hour (rat) LC50 is 11 ppm.

    LC
    50m = 1 / [0.01 / (11 2)] or 2,200 ppm. Therefore the mixture is neither toxic nor highly toxic. Note that the 4-hour LC50 of 11 ppm was normalized to 1-hour by use of Section E103.1.3.1.
TABLE E103.1.3.1
NORMALIZATION FACTOR
TIME (hours) MULTIPLY BY
0.5 0.7
1.0 1.0
1.5 1.2
2.0 1.4
3.0 1.7
4.0 2.0
5.0 2.2
6.0 2.4
7.0 2.6
8.0 2.8

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