This is a question from the past looking for an opinion based on your knowledge and experience.
In the 1600's and 1700's more than one British warship was blown up under unknown circumstances. I have come upon an article which, paraphrased, says that " a seaman was sent below decks where he was overcome by something he described as a terrible smell. He was brought to the open deck where he regained conciousness under the ministrations of the ship's doctor"
We know that a part of the life of every ship was when it was placed IN ORDINARY, or, when the crew is removed, the ship anchored and looked after by a few Warrent Officers (5 or 6) It is well known that during inclement weather the personnel on board did not expose themselves to the elements in order to relieve themselves (the normal method was "at the cathead" in the foremost part of the ship which was exposed to the sea and the elements. Ships remained in ordinary for months and sometimes years. The bilges (the underdeck portion at the very bottom of the ship's internal structure) which was not ventilated purposefully and was covered by a complete deck. Gases could escape but restricted by the lack of free air flow. We can presume that bacteria was everpresent in the bilges along with fresh water filtering down from above, waste water generated by the use of caustic soaps and cleaning substances as well as leakage of salt water from the outside.
Is it remotely possible that enough methane could collect under these circumstances and be ignited by the ever present lanterns below deck.
From what I have told you, am I working in the right direction to seek a possible cause for these explosions? DR