Also, this is not a measurement that yields symmetric action, since it’s harmful in only one direction. Your actions based on the same level of accuracy are likely to be different.

If a device can tell you something is maybe poisonous, a positive result is going to lead to very different behaviour than a negative one, even if they’re equally likely to be accurate. This is especially true when your priors (ie research with accurate devices and knowledge of combustion) lead you to expect (prior to measurement) that it will indeed be poisonous.