The original static system SiH4 pyrolysis product-time evolution data of Purnell and Walsh have been modeled with a mechanism involving 15 gas-phase elementary steps together with five alternative solid deposition processes. The gas-phase steps incorporate the most recent experimental and theoretical information concerning the kinetics and thermodynamics of the transient intermediates, SiH2, SiH3SiH, and H2Si=SiH2, and the isomers of Si2H2 and Si3H6. Although the observed kinetic behavior can be fitted with reactive transients H2SiSiH2, Si2H2, or Si3H6 as the species leading to solid deposition, it is only possible with unrealistically large wall termination (or polymerization) rate constants. Trisilane, Si3H8, offers a better alternative solid sink process with realistic rate constants but leads to a prediction of kinetic wall effects which are not observed. In the overall process the observed rate acceleration and transition between 3/2 order and first-order kinetics is accounted for by the reaction Si2H6 --> SiH3SiH + H-2 whose rate is enhanced by chemically activated Si2H6 produced via SiH2 insertion into SiH4. This finding is independent of mechanisms of solid deposition.