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Falls of Ground Incidents - Reporting Year 1996/1997

Contents

Introduction

This report summarises the fall of ground dangerous occurrences and fatal and major injury accidents reported at mines during the 1996/97 reporting year.

All statistics are provisional.

Dangerous occurrences

Any fall of ground, not being part of the normal operations at a mine, which results from a failure of an underground support system and prevents persons travelling through the area affected by the fall or which otherwise exposes them to danger was introduced as a dangerous occurrence at Part II/40 in RIDDOR 1995, with effect from 1 April 1996.

Thirteen falls of ground were reported at coal mines during the year. None were reported at other (miscellaneous) mines.

Most of the falls were in recently excavated places, 8 had been excavated less than six months previously, and 11 in the last two years.

In 7 incidents there was no warning of the collapse. Previous inspections of the places where the falls occurred had not revealed any signs of impending failure. A further 5 incidents gave less than 24 hours notice. Particular attention should be paid to the identification of warning signs at an earlier stage so that there is sufficient time from the discovery of an incipient fall to take recovery action which will prevent the fall from happening. One mine, which has had four falls, has started to install rockbolt type tell-tales at junctions to give early indication of strata movement in a low stress geotechnical environment.

Most falls occurred in places using free-standing, passive, support such as arches or props and bars (see table). Eleven incidents occurred in passively supported places and two in rockbolted places.

One fall resulted in one man being killed and two others being seriously injured. The fall occurred at a small coal mine within an in-seam tailgate development, advanced by an arc wall cutter and shotfiring. The normal support system was props and bars but this had been strengthened to 4.2m RSJ girders set on 1.7m captivated RSJ legs in the zone where the fall occurred. A clay filled joint in the massive limestone roof had been encountered in the heading near to the roadway centre giving rise to a cavity when the clay fell away as the heading advanced. This cavity exposed a calcite filled joint along the left hand side. The fall occurred from the face to 11m outbye. Three persons were injured with one sustaining a fractured ankle and one being detained in hospital for more than 24 hours. The command supervisor suffered fatal injuries.

Coal mines - Fall of ground dangerous occurrences

Type of Support
Free-standing support 11
Rockbolting 2
Total 13
Warning of Collapse
None 7
Less than 24 hours 5
Over 24 hours 1
Total 13
Age of Excavation
Recently driven 8
6 - 12 months 8
1 - 2 years 1
2 - 5 years 2
Over 5 years 1
Total 13
Type of Excavation
Junction -girders 4
Roads - rockbolts 2
Roadway - props and bars 5
Roadway - arches 1
Faceline - props and bars 1
Total 13

Accidents

There were two fatal injury accidents and 29 major injury accidents at coal mines compared with no fatal injury and 38 major injuries in the previous year. (Note: The definition of a major injury accident was extended on 1 April 1996. Seven of the 29 accidents were reportable solely as a result of the new classification).

At other mines there were two major injury accidents, compared with one in the previous year.

At coal mines 16 of the accidents occurred in places supported conventionally , 11 occurred where powered supports were used and 4 where rockbolts were used. Fourteen accidents were at a longwall face, 15 were in headings and 2 occurred elsewhere underground.

1995/1996 1996/1997
All mines fall of ground accidents Fatal Major injury Fatal Major injury
Coal mines - free standing supports (arches, props and bars etc) - 18 1 15
Coal mines- powered supports - 9 - 11
Coal mines- rockbolts - 11 1 3
Miscellaneous mines - 1 - 2
Total 0 39 2 *31
*7 accidents were reportable as a result of the new RIDDOR 1995 classification

One of the fatal accidents has already been mentioned under the Dangerous Occurrences heading. The other fatal injury occurred at a large coal mine, in a rockbolted development. A development worker was in the process of rockbolting near to the face of a 5.0 m × 3.6 m drivage, in advance of the last permanent supports, when he was struck by a fall of coal from the side of the roadway.

1995/1996 1996/1997
Coal Mines - place of accident Fatal Major injury Fatal Major injury
Longwall face - 13 - 14
Headings - 22 2 13
Elsewhere - 3 - 2
Total 0 38 2 *29
*7 accidents were reportable as a result of the new RIDDOR 1995 classification

Conclusions

The introduction of the fall of ground category of dangerous occurrence has focused attention on the limited knowledge of strata behaviour in some passively supported places.

Falls at junctions have made a disproportionate contribution to the total.

This first year has highlighted the requirement that there should be sufficient time from the discovery of adverse ground conditions to allow recovery to take place.

SP Wing, HMPIM

2012-11-27