On a very hot afternoon on 30 June 1869, two carts, each containing a ton of nitro-glycerine (then known as powder-oil) set out from Caernarfon travelling the 8 miles to the Glynrhonwy slate quarry on the edge of Llanberis. Although the canisters containing the liquid explosive had been carefully packed into a boxes containing sawdust and covered in straw when loaded onto the carts, nobody at the time knew how inherently unstable nitro-glycerine was!
Just before 6pm, immediately after the carts had passed the Cwm-y-Glo station goods shed, the cargo exploded with what was probably the loudest man-made explosion ever heard up to that time. Both carters died, plus a passing quarrymen from Glynrhonwy and two young boys aged 11 and 13, who were unlucky enough to be nearby. The inquest showed that the carters had spent some time at the Alexandria Inn in Cwm-y-Glo which meant the carts were cooking nicely in the sun.
No trace of the carters, horses or carts remained at the site and two deep craters approximately ten feet deep were left behind. Human and animal remains, as well as parts of the carts, were spread far and wide – with some of the debris being found in the neighbouring village of Brynrefail. The damage to Cwm-y-Glo’s buildings was extensive, many having roofs blown off and windows destroyed. Scarcely a house in the village escaped without damage. A wheel and harness from one of the carts landed a half-mile away and, to this day, the spot is marked by a large ‘X’ scratched on a stone wall which locals keep visible.
The far-reaching consequence of this event was the Nitro-glycerine Act 1869 prohibiting the manufacture, transport or sale of nitro-glycerine or any product containing it in the U.K.
A ballad about the accident (see the excellent Welsh cultural history site,‘ Gathering the Jewels’) The text of the song translates roughly as:
Dear quarrymen and all rockworkers throughout Arfon and Meirionydd. Hear about this alarming and terrible accident that has made many hearts sad. There has been accident after accident in the quarries, with falling loose rocks from morning to noon. They tear the flesh and break the bones and people collect bodies in blankets and sheets. What heart does not melt at the sight of a mother unable to recognise her son or husband, the tears pouring from the children shouting: ‘Dad, where are you?’. And things are far worse with nitro-glycerine. We’ve had terrible disasters at Abergele, now we have one at Cwm y glo ”
The full Welsh text and a transcription of a contemporary account of the explosion in the Times of 2 July 1869 can be found by clicking on this website
More reading: Death Blast in Snowdonia by T Meirion Hughes.