Peter Smith in the London Times:
Early one freezing January morning in 1896, a massive explosion ripped through the Tylorstown Colliery in the Rhondda Valley. The force of the explosion blew the roof off pitshaft number 7 and sent a “black tornado of dust up through the shafts”. A quick count of the missing miners’ lamps suggested that more than 100 men were below. In addition, there were the boys, known as “the trappers”, employed to open and close the thick wooden doors in the pitch-black tunnels.
Alerted by a Home Office telegram, Dr J. S. Haldane arrived as quickly as the train connections from his Oxford laboratory would allow. The 35-year-old physiologist had been instructed to determine the cause of death and to test a theory. It was generally believed that deaths from such explosions were caused by blast injuries.
Haldane thought differently. He was convinced that three quarters of fatalities were due to suffocation from gases seeping into tunnels. But as Haldane talked to the Tylorstown rescue party, he found that the toxic gas produced after the explosion – known as “afterdamp” (damp from the German for steam, Dampf) – had not extinguished the miners’ lamps. This meant oxygen was present and therefore suffocation must be ruled out.
Even though it threatened his theory, the man The Times once described as a “medical detective” was excited by this intriguing new evidence. In order to explain what had happened, Haldane had the unenviable task of visiting the bereaved families to examine the bodies of the dead miners. Here he found the evidence he needed. From the pink and red appearance of their skin, he suddenly understood why so many miners were dying in pit explosions: carbon-monoxide poisoning. A distinctly carmine-red blood sample provided the final proof.
More here.