I don’t know who actually started the fire, but we wouldn’t have heard about this if Henry had kept his lips sealed, which he obviously did not since we know about it.
We didn’t start the fire!
Was Henry in the kitchen when the fire started?
In the lantern room?
He was on duty and when he examined the lantern room, found it to be on fire.
Part of the lighthouse that was made molten by the fire?
Glass?
Metal?
A melted giraffe?
I’m thinking the light apparatus/area melted and fell/dripped on him.
yeppers
Did he step/fall into a puddle of molten metal?
Nope.
Did the molten metal exude some sort of gas or other pollutant that he breathed in, and subsequently died 12 days later from his lungs being damaged? Like from pneumonia or similar?
Nope.
Did he eat this metal thing?
Yes. Someone want to put the whole thing together?
So was the cause of death:
- Internal burns?
- Internal laceration?
- Some kind of blockage?
Did he eat the metal because it was encased in something else?
Was it mercury?
A drop of molten lead fell into his mouth down to his stomach. A combination of severe burns to his esophagus and the liquid metal being in his stomach.
In a bit, I can share the whole story.
Consider this for the most part solved. I’ll post the story.
Ahh… I forgot that the injury was something noticed immediately by the witnesses. I was thinking of something that gradually became apparent over the 12 days
A fire broke out and the lead coverings of the lanterns dripped. By terrible luck, Henry got a drip of molten lead in his mouth, straight down his throat. He screamed, “God help me, I’m on fire inside!”
Here is a picture of the metal they pulled out of him during his autopsy, which confirmed his story.
And his plaque:
Note: I did not consider this poisoning despite the plaque saying lead poisoning. I think he died from the damage done to his body inside, not from poison.
I didn’t mean to throw anyone off with the poison answer that I gave being “no”.
Ah very interesting (and grim) story 
I have to say though, it reminds me of something which happened just last year.
Men broke into a house in Pheonix, and shot and killed a woman there, and shot a man twice in the head. Police showed up and…arrested the shot man. They didn’t believe him when he said he had been shot in the eye, and it wasn’t until after 6 hours of questioning that he finally got to see a medic.