We just used to use standard hospital bacteriocidal spray on all surfaces to clean. I don't know why anyone would use formaldehyde to disinfect anything, but I particularly would NOT recommend it for an airtight chamber in which humans are periodically sealed for up to 3 - 4 hours at a time.
Sorry, I´m afraid my question is not well expresed. I`m not using pure formaldehyde, is a trialdehyde, recommended by Navy (US Navy too), but like you, I think is dangerous unless the use of the chamber is delayed for hours. But my question is what product do you use? and Is the same for helmets, tubes and masks? Thanks