Those gases are not "harmless" by any metric. They must be promptly used or they are a much larger problem than the plastics. But the GPs point seems to be tha

Those gases are not "harmless" by any metric. They must be promptly used or they are a much larger problem than the plastics. But the GPs point seems to be that only those two specific kinds of plastic vaporize into those tractable gases. Most of them become all kinds of things, from wild poisons to chemical nightmares that will destroy your equipment.