Background
Seams
The Lanarkshire coalfield in the vicinity of Blantyre had three seams of coal being worked in the 1870s. They were the ell coal,7 feet (2.1 m) thick at 117 fathoms (702 ft;214 m);the main coal,4.5 feet (1.4 m) thick at 129 fathoms (774 ft;236 m) and the splint coal,5.5 feet (1.7 m) thick at 155 fathoms (930 ft;283 m). Precise depths vary with the elevation of the top of the various shafts. [1]
The Blantyre colliery had five shafts:
- No. 1,24 feet (7.3 m) by 8 feet (2.4 m) working the ell and main coals.
- No. 2. 16 feet (4.9 m) by 8 feet (2.4 m) working the splint coal.
- No. 3. 24 feet (7.3 m) by 8 feet (2.4 m) working the splint coal.
- No. 4. 24 feet (7.3 m) by 8 feet (2.4 m) working the splint coal. At the time of the explosion No. 4 had not yet connected with the rest of the colliery.
- No. 5. 10 feet (3.0 m) diameter used as the upcast [lower-alpha 2] for numbers 1,2 and 3. [1]
Numbers 2 and 5 shafts were close to each other,within 30 yards (27 m). Number 3 shaft was 680 yards (620 m) away. Number 1 shaft was between the two but only reached the ell and main coals. Blind pits,that is shafts that do not extend to the surface,connected the ell and main coals to the splint coal. [1] The main coal ceased to be worked in November 1878 and the passages from shaft 1 bricked up. Shaft 1 continued to work the ell coal. [2]
Four main districts were formed in the splint coal:
- A smaller area with workings to the north and south of number 3 pit.
- An area lying in the north-west quadrant from number 2 pit.
- An area lying in the south-west quadrant from number 2 pit.
- An area lying in the south east quadrant from number 2 pit close to,and in communication with,the workings from number 3 pit. [10]
Conditions in the mine were held to be poor by the colliers. The previous year the miners had sought a wage rise to compensate for the poor safety and been refused. They went on strike and were immediately sacked. Since the miners lived in tied cottages they were therefore evicted by force. The mine owners then brought in Irish Catholics to work the mine. [11]
Workings
Most of the coal was worked using the Newcastle system,also known as "pillar and stall" or "stoop and room". A heading was driven into the coal and at intervals along it rooms were excavated,around 12 feet (3.7 m) wide. As the rooms got deeper another heading was driven from room to room to leave pillars (or stoops) about 20 yards (18 m) square behind. During this stage only around 30% of the coal was extracted. Eventually the whole district consisted of a grid pattern of passageways around stoops. The final stage in extraction was "stooping". The furthermost roof was supported by pit props and the stoops removed. Once a complete row of stoops had gone the props were removed from the furthest part which would collapse into the space ("goaf" or "gove") behind. During this process settlement and fracturing of the roof and seams above could occur,potentially releasing larger quantities of gas. [1]
The alternative method of working the coal was the longwall system. Two headers were driven forward to the far end of the district and an interconnecting passageway excavated. The passageway was supported by props and the long wall on the shaft side of the passage excavated. As this wall retreated the roof was propped and the furthermost props removed,allowing the overburden to collapse into the goaf. With longwall the same fracturing and gas release that stooping could cause was always present. [1]
The ell coal was mainly worked by stoop and room,with longwall in the southern part only. The main was exclusively worked by longwall and the splint (apart from a trial section) worked by stoop and room. [1]
Ventilation
In collieries at that time air circulation was induced by a furnace at the base of the upcast pit. Hot air rising up the pit,as if up a chimney,drew the exhausted and contaminated air out of the galleries. Downcast pits let the fresh air in to replace it. The route the air took was carefully controlled by doors and partitions. At Blantyre pit,number 5 was the upcast shaft for pits 1,2 and 3. About 5 tons of coal were burnt per day in two out of three grates,each 7 feet (2.1 m) by 4 feet (1.2 m). [1]
Air for the ell coal was drawn down pit number 1. At the base it split north and south then after passing around the respective parts of the workings it was led to the upcast pit. [2]
Ventilation in the splint coal was more complex. Air from number 3 pit was split in two and passed along the north and south levels. After passing through the respective workings the two currents passed through the north and south headings before recombining on the "rise" (west) side and passing into the workings of number 2 pit. On average the air circuit was 2,400 yards (2,200 m) in number 3 pit. [1]
Air was drawn down number 2 and split in two. The larger portion went north,circulated around the north-west workings for 3,674 yards (3,360 m) before returning to the upcast pit. The smaller part was led to the south,circulated around the south-western area for 2,901 yards (2,653 m) and then back to the upcast. The air from number 3 pit entered the workings associated with number 2 pit in the east and circulated around number 2 pit's south-eastern portion before finally reaching the upcast. The air circuit at 3,500 yards (3,200 m) might not be considered excessive,but when both pits are added the total circuit was 8,096 yards (7,403 m). [1] After the disaster this policy of using the air from number 3 workings to ventilate number 2 workings was roundly condemned in the trade press:"It is a very dangerous system,and should be abandoned at once". [12]
