First and second limits lower pressures

The two types of behaviour discussed earlier with respect to surface destruction efficiency are well illustrated at the first limit by the results under the conditions of Hinshelwood and Moelwyn-Hughes [13] (high e) on the one hand, and of Semenova [16] (low e) on the other. The contrasting effects of inert gases in the two types of vessel are shown in Tables 3 and 4. At the first limit the surface destruction refers to removal of H, OH and O. 

Observed and calculated first limits with 51 mm diameter KCl coated vessei at 500 °C [54] 

calculated assuming only moderate efficiency for destruction of H atoms, with B of eqn. (13) = 7.8, 

Taking reactions (i)—(v), together with the surface destruction of H and O atoms, the stationary state treatment gives the complete first and second limit explosion boundary as 

If the diffusion coefficients of H and O atoms in the gas mixtures can be estimated satisfactorily, then the results of the above treatment can be used also to derive values of the rate coefficients fe2 and k. Using estimated hard sphere values (Dq = Xqc/3 where Xq is the mean free path at unit pressure and c is the mean molecular velocity), Baldwin obtained, at 520 °C 

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