According to the MSDS Berryman's injector cleaner using H.E.S.T. is acetone. It is in some of their fuel system cleaners. Seafoam fuel injector cleaner uses Benzene. I presume both are safe otherwise a lot of customers would have put them out of business. Gas engines of any kind should be run occasionally to promote the consumption of fuel before it goes stale and also to keep the engine lubricated.