Upper and Lower Ignition Limits

Though Eq. (39.1) is obtained for a simplified reaction mechanism disregarding the processes proportional to the product of the concentrations of active centers (those processes involving H2O and H2O2, as well as heterogeneous OH and 0 decay (for details see [230]), it enables a quantitative interpretation of certain gross features of this reaction. Consider first the ignition limits. 

With 9 0 and high t values, [H] becomes constant, [HJg = W0/I9I representing the steady-state concentration of active centers. 

the transition from a stationary to a non-stationary reaction state involves a change of the 9 sign, i.e. the critical condition for the transition is 

Expressing the values Vg, Vg and V14 by the relevant rate constants and pressure p in the same manner as above, we obtain the expression for the lower (pj) and the upper (pg) ignition limits. 

---

In comparison to toxicity the fire takes effect in relatively small area. It is given by the fact, that for the gas ignition there are necessary concentrations between upper and lower ignition limit. Lower ignition limit is mostly higher than toxic gases dangerous concentrations. 

---