That's like linking smoking to cancer. Hard to do, but you know that the rates of cancer go down for non-smokers so it seems to be deducible. The effect of dirt on electronics is not quite as simple as mechanical wear and tear (cycling and so forth, but that also occurs), but rather an increase in the accumulation of straws on the proverbial camel's back. When a circuit board fails because its resister burned out, was it because of a manufacturing defect in the resistor or all the dust and gunk on that board insulating the conformal coating; or was it the effect of the defect exacerbated by the aforementioned gunk? If that gunk was not there or substantially reduced, would the part have failed at all?
In reality, the overall effect is very small, but even small effects on multiple million-dollar gear are somewhat relevant. I guess for morale and other reasons, the decision was made to favor allowing smoking inside subs. That is apparently under review. Just as women in subs is now becoming a reality. Hope they enjoy the newfound drama; I know I did!
