An interaction can best be defined as a violent reaction that interrupts normal conditions. Interactions become apparent when there is an intense outcome created by chemical, thermal, or physical responses to the combination of two or more variables.
If a flaming wick is inserted into a combustible gas stream, for example, there will be a flash as the gas ignites. This is an interaction. See Figure B-1.
Two or more conditions must be present to cause an interaction, as in the case of the piston-stuffing example discussed in Appendix A. Machining A was to specification but not at the nominal dimension. The ...