The commentary doubles as a synopsis and has therefore been reproduced in full:

Wherever coal is cut, the men who mine it face yet another potential hazard. This time, it's invisible. It's without smell, it's methane - a gas miners often call firedamp.

Most of the firedamp is diluted and blown out of the mine by the ventilation. But, as the name implies, firedamp is inflammable, and although no naked flames are allowed in any British mine, it can be ignited by other means. If it's not caught quickly, a small ignition can cause a large fire. Firedamp has been known to burn for up to half an hour before being put out.

Firedamp ignitions are usually set off by the picks on fast-moving power-loading machines. Miners have to be able to recognise bands of hard rock in the coalface which will give off a spark when struck. The machine won't differentiate: it takes all before it. It's the job of the machine operator to avoid cutting into incendive rock.

To find out more about the way firedamp behaves, scientists use a mock-up face on the surface. They feed firedamp into the strata, and as the machine cuts its way along the face the firedamp, here given an orange colour, is monitored and measured. In a mobile laboratory, records are built up, and we can now tell where firedamp is likely to accumulate. On some machines, additional ventilation can be built in. Routine sampling of the gas is an essential part of safe working practice.

It's important too that small coal shouldn't be allowed to accumulate on top of the machine and impede ventilation. It's vital that the machine operator knows the dangerous rocks from the harmless. This is pyrites, found in many of our coal faces. Hard pyrites will cause ignition. So will sandstone, which contains grains of quartz. Picks on a machine striking stone can get very hot. Blunt picks get even hotter. In the laboratory, a block of sandstone is rotated against a pick to find out exactly when ignition takes place. The experiment is carried out in a flammable mixture of firedamp and air, just as in the mine.

Underground, geologists are constantly on the lookout for fresh hazards. Their investigations can predict the strata which lie ahead. But constant vigilance is the best safeguard - the vigilance of supervisors who can test and measure for the incidence of gas. The vigilance of the machine operator. The vigilance of ventilation men, who check the velocity and the amount of the air in circulation. Good mining practice, and everyone's awareness and co-operation, can help to minimise yet another of the hazards men face to win the coal.