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Introduction Note - This is the printer friendly format of this page. Refresh your browser for the screen version.
Groundfall accidents have been the leading cause of fatalities in the underground coal mining industry for many years. Statistics from the Mine Safety and Health Administration (MSHA) indicate that approximately
one-quarter of the victims of these fatal accidents were in an area where no devices had been installed to support the mine's roof. Mine operators rely primarily on threats of disciplinary action and classroom safety lectures to discourage miners from going under unsupported roof. However, several other options may also be worth pursuing:
- Eliminate sources of motivation for going under unsupported roof by changes in equipment, work procedures and policies.
- Eliminate the precursors of going under unsupported roof via incentives or feedback.
- Increase fear of the harm that roof falls can cause.
- Conduct behavioral modeling to show supervisors how to interact with miners who they find under unsupported roof.
- Have high level managers communicate their commitment to the goal of keeping people away from unsupported roof.
- Use disciplinary actions.
This article summarizes the opinions of 268 coal miners and 29 first-line supervisors concerning why people go under unsupported roof and how to prevent this behavior. The interviews were conducted at six mine sites during 1989 and 1990.
For additional information on this topic contact:
Robert Peters
Pittsburgh Research Laboratory
412-386-6895
RPeters@cdc.gov
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![Miner installing a post](images/installing%20_post.jpg) |
Background
Going under unsupported roof is a very dangerous activity. It directly contributes to many fatalities and severe injuries in the underground coal mining industry. According to MSHA's accident statistics, in most years, roof fall accidents continue to be the leading cause of fatalities in underground coal mines. During the 5 year period
1997-2001, 51 coal miners were killed by falls of roof and rib, and over 2,300 were injured.
Fortunately, the number of coal miners killed each year by groundfalls has been declining since we interviewed miners about going under unsupported roof in
1990. At the time of that study, about half of the miners who were killed by roof falls were in an area of unsupported roof. Not only has the number of
deaths caused by roof falls declined since 1990, the proportion of these victims who were under unsupported roof at the time of the roof fall has also declined--from
approximately one-half to one-quarter. Nevertheless, it is important to keep in mind that the factors contributing to this type of fatality are still present,
and that miners and mine operators should continue to be very diligent in their efforts to prevent people from going under unsupported roof.
Groundfalls have been a major threat to miners' safety ever since mining began. Most miners are told repeatedly that it is very dangerous to go under unsupported roof and know that mine safety regulations prohibit this behavior. Nevertheless, accident investigations and data from interviews with coal miners suggest that there are individuals in the coal mining work force who, in certain circumstances, do not hesitate to go under unsupported roof.
Some of the reasons for going under unsupported roof are directly related to the task being performed. However,
there are other factors:
- the miner's perception of the company's policy concerning going under unsupported roof and how it is enforced,
- the attitudes and behavior of the employee's supervisor and coworkers,
- the employees' own attitudes and expectations regarding the risks and benefits of doing things under unsupported roof.
Interview data were also collected on these other factors. The complete findings from interviews with 297 miners can be found in Bureau of Mines IC Report No. 9300 (4). The focus of this paper is limited primarily to miners' views about what types of activities are likely to be performed under unsupported roof, and what types of actions might help to prevent miners from performing these tasks under unsupported roof.
How the Information Was Collected
A sample of miners and section supervisors was asked to respond to a variety of questions concerning going under unsupported roof in one-on-one interviews. All interviews were conducted in private, usually at
the dinner hole near the miner's worksite. Employees were interviewed only if their job required them to work near face areas of the mine on a daily basis. All participants were assured that their responses would be held in confidence and were told that their participation was completely voluntary.
Data were collected from February 1989 to March 1990. A total of 297 employees from six underground coal mines participated in the study. The table below shows the mine, the number of miners interviewed, the number of underground employees, the location, the rate of lost-time injuries per 200,000 hours of exposure, the seam height, and whether or not miners were represented by a union. All mines were using the room-and-pillar method of extraction, remotely operated continuous miners, and roof bolters equipped with automated temporary roof supports.
Table 1.–Characteristics of Mines Included in Sample
Mine |
Number of miners interviewed |
Number of underground employees |
Location |
Injury rate1 |
Seam height, in |
Union |
A |
66 |
437 |
West PA |
19.14 |
48-54 |
Yes |
B |
45 |
260 |
East OH |
9.32 |
66-72 |
Yes |
C |
56 |
235 |
West MD |
28.07 |
84-96 |
No |
D |
53 |
430 |
South IL |
6.35 |
84 |
No |
E |
50 |
480 |
North AL |
4.50 |
40-42 |
Yes |
F |
26 |
50 |
West CO |
2.05 |
84-90 |
No |
1Per 200,000 employee-hours of exposure.
Note that the results of this study are not representative of the entire industry. The sample of mines that participated in the study was small, and it was not randomly selected. Several mining companies who were invited to participate in the study were unwilling to do so.
Reasons For Going Under Unsupported Roof
Miners were asked three sets of questions concerning why people sometimes go under unsupported roof. In the first set of questions miners were asked to describe an incident in which they have recently observed a coworker doing something under unsupported roof. The second set of questions asked miners to describe the most recent instance in which they unintentionally went under unsupported roof. The third set of questions asked miners to identify tasks that are
likely to be performed under unsupported roof by people who perform their type of job (e.g., roof bolters).
Observations Concerning Coworkers
One way to determine what might cause miners to go under unsupported roof is to ask them to describe a recent incident in which they observed a coworker doing something under unsupported roof. Miners were asked several questions concerning such incidents. They were first asked,
![Red diamond](images/red_diamond.gif) |
Have you ever seen someone go under unsupported roof? |
86% said that they could recall an instance in which they had seen someone go under unsupported roof. Miners were next told,
![Red diamond](images/red_diamond.gif) |
Consider the most recent time you saw someone go under unsupported roof. Has it been within the past 6 months? |
Of the 225 miners who said that they had seen someone under unsupported roof, 130 (58%) said that the most recent time had been within the past 6 months.
These 130 miners were asked several questions about the most recent incident. The questions and their responses are listed below:
![Red diamond](images/red_diamond.gif) |
Do you think
this person was aware that he/she was under unsupported roof? |
Yes |
71.5% |
No |
27.7% |
Uncertain |
0.8% |
![Red diamond](images/red_diamond.gif) |
Did this person take a look at the roof before he/she went under it? |
Yes |
59.2% |
No |
28.5% |
Uncertain |
12.3% |
![Red diamond](images/red_diamond.gif) |
How far inby the last row of
supports did he/she go? |
0 to 5 feet |
52.3% |
6 to 10 feet |
30.0% |
Over 10 feet |
17.7% |
![Red diamond](images/red_diamond.gif) |
How long was he/she there?
|
A few seconds |
54.6% |
1 or 2 minutes |
22.3% |
Under 10 minutes |
12.3% |
10 to 20 minutes |
7.7% |
Over 20 minutes |
3.1% |
These responses suggest that 72% of those who reported recently seeing someone under unsupported roof thought that the incident had been an intentional act. In about half of the incidents that were described, it appears that the people under unsupported roof had tried to be cautious about their behavior. They looked at the roof before going under it, they went less than 10 ft beyond the last row of supports, and they were under unsupported roof for only a few seconds. Of course, miners may behave differently when they realize that someone could be observing them than when no one is present. It could be that miners who go under unsupported roof are less cautious about it when they know no one is around to observe them. Miners were also asked to describe what the person who they observed under unsupported roof was doing. The most frequently mentioned replies were as follows:
- Walking through unbolted crosscuts (17)
- Walking (11)
- Operating a continuous miner (11)
- Hanging or extending ventilation tube (10)
- Retrieving things left laying on the ground (7)
- Marking the roof (5)
- Rock dusting (5)
- Repairing a continuous miner (4)
- Operating a scoop (4)
- Operating a mobile bridge (3)
- Examining a roof fall (3)
- Restoring power to a remote continuous miner (3)
- Carrying supplies (3)
- Operating a roof bolter (3)
Miners were next asked:
![Red diamond](images/red_diamond.gif) |
Does this person often go under unsupported roof? |
Yes |
15.4% |
No |
76.9% |
Uncertain |
7.7% |
Relatively few persons indicated that the person they had most recently observed under unsupported roof was doing it on a frequent basis. (However, at each mine, at least a few miners would mention that, although going under unsupported roof was not common at the mine where they were currently working, it was done rather often at mines where they used to work.)
If the miner's response to the question above was "No", the miner was asked, "Had anything unusual happened on that day that might have caused this person to go under unsupported roof?" Most were unable to identify any type of unusual event or circumstance. Those who were able to cite something unusual thought that the following events or circumstances may have been at least partially responsible for why the person had gone under unsupported roof:
- There had been a roof fall (5)
- The roof had fallen on the continuous miner (2)
- A rib fall had tripped the circuit breaker on the continuous miner so it could not be operated by remote
(1)
- Poor roof conditions had caused us to get behind on production (1)
- The person had only recently been assigned to the job that was being performing
(1)
- The continuous miner was broken down and could not be moved (1)
- An unbolted area had been partially rock dusted (1)
- There had been a power outage (1)
- We were working on a Saturday to get caught up on production (1)
Unintentionally Going Beneath Unsupported Roof
Some of those who go beneath unsupported roof may not realize that they have gone beyond the last row of bolts, i.e., their action was unintentional. Miners were asked questions to determine whether this happens very often and to find out what activities are usually being performed when people unintentionally go under unsupported roof.
![Red diamond](images/red_diamond.gif) |
Miners were first asked if they had ever unintentionally gone into an area of unsupported roof. |
Eighty-two percent of the sample indicated that they could recall such an incident.
![Red diamond](images/red_diamond.gif) |
Those who could recall a time that they had unintentionally gone under unsupported roof were asked to estimate how long ago the most recent incident had occurred. |
Approximately 60% of those who could recall an instance in which they had unintentionally gone under unsupported roof estimated that the most recent incident had occurred within the past year. About 24% thought that the most recent incident had occurred within the past month.
Miners were next asked:
![Red diamond](images/red_diamond.gif) |
What were you doing when you realized you were under unsupported roof? |
The most frequently mentioned replies were:
- Walking (59)
- Hanging or extending ventilation tube (11)
- Operating a scoop (9)
- Repairing a continuous miner or bolter (8)
- Hanging ventilation curtain (8)
- Rock dusting (7)
- Operating a bolter (7)
- Operating a continuous miner (6)
- Carrying supplies (6)
- Setting timbers (5)
- Operating a ram car or shuttle car (4).
Several of those who said that they were walking somewhere when they discovered that they had gone under unsupported roof noted that no warning devices had been posted at the last row of bolts. In a few cases, miners noted that the area they were walking in had been rock dusted, leading them to believe that it was bolted. At one mine, several miners noted that the sliding (telescoping) ventilation tubes would often become jammed, causing miners to have to go to the end of the slider closest to unsupported roof and pull on it to get it to fully extend.
In summary, it appears that a significant proportion of people who work at the face unintentionally go under unsupported roof. This suggests that it is very important that warning signs always be posted at the edge of unsupported roof, and that these signs are highly visible.
Job-Specific Reasons
To determine what might cause miners who perform a particular face crew job to go under unsupported roof, each participant was asked to respond to the following open-ended question:
![Red diamond](images/red_diamond.gif) |
Considering the different tasks involved in doing the [INSERT MINER'S JOB TITLE (e.g., roof bolter's)] job, which ones are most likely to cause them to go under unsupported roof? |
The table below lists some of the most frequently cited tasks and indicates the number of people from each job category who mentioned it. For example, the first column of numbers shows the number of continuous miner operators or helpers who mentioned each task listed along the left side of the table as being likely to cause miner operators or helpers to go under unsupported roof.
Table 2.– Activities cited as likely to cause miners to go under unsupported roof
Activity |
Job Title |
Miner operator |
Roof bolter |
Mechanic |
Haulage operator |
Scoop operator |
Section supervisor |
Other |
Walking through unbolted crosscuts |
2 |
2 |
2 |
6 |
|
5 |
9 |
Unintentionally walking (no signs) |
|
2 |
1 |
|
|
3 |
4 |
Hanging ventilation curtains |
8 |
1 |
|
6 |
|
|
1 |
Hanging or extending ventilation tubing |
11 |
1 |
|
9 |
|
2 |
4 |
Cleaning up and resupporting after roof falls |
|
8 |
|
1 |
|
2 |
2 |
Restoring power to continuous miner |
14 |
|
3 |
2 |
|
4 |
|
Repairing continuous miner |
8 |
|
9 |
|
|
2 |
|
Retrieving wrenches and steels |
|
18 |
|
|
|
1 |
|
Operating the scoop beyond supports |
|
|
|
|
13 |
|
3 |
Advancing the shuttle-ram car beyond bolts |
|
|
|
18 |
|
|
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Preventive Measures
As previously explained, miners were asked to identify tasks that are likely to be performed under unsupported roof by miners who do their type of job. Whenever miners identified such a task they were also asked the following question:
![Red diamond](images/red_diamond.gif) |
What could be done to make it less likely that [INSERT MINER'S JOB TITLE] would go under unsupported roof while [INSERT TASK CITED]? |
This section presents miners' ideas about actions that might be taken to make it less likely that miners would go under unsupported roof to perform various tasks. Some of their ideas may not yet be feasible given the status of current technology and the resources typically available to mine operators.
Activity Associated With
Going Under Unsupported Roof |
Suggested
Countermeasures |
Hanging Ventilation Curtain |
- Use spring loaded ventilation curtain.
- Use miners equipped with scrubbers so the ventilation curtain does not have to be kept so close to the face.
|
Hanging or extending ventilation tube |
- Use telescoping ventilation tubes (sliders).
- Put a handle on the end of the slider so it can be extended by pushing on the handle with a long pole.
- Devise a way to attach the slider to the continuous miner so it will automatically feed out as the miner advances.
|
Repairing continuous miners or bolters that break down under unsupported roof and cannot be
moved |
- Perform better preventive maintenance.
- Perform pre-operation maintenance checks.
- Communicate potential equipment problems to those who will be using the equipment on the following shift.
- Ensure that an adequate supply of timbers or safety jacks is kept reasonably close to the face.
- Set temporary supports to protect the mechanic; and a warning sign should be posted so the mechanic will realize that the machine is under unsupported roof.
- Make clear who is responsible for setting temporary supports in these situations.
|
Restoring power to a remote continuous miner |
- Develop a method of resetting the breaker from the remote, the power center, or some place that is outby the last row of bolts.
- Develop a guard that will protect the power off button or emergency stop button from being accidentally activated if pieces of coal fall into the operator's compartment.
|
Advancing the continuous miner beyond supports when the machine is being operated from the cab. |
- Hang long warning flags from the last row of bolts on the side that the operator can see most easily.
|
Pulling the continuous miner cable |
- Develop a reel for taking up slack in the cable.
|
Cleaning up and resupporting the roof after large and/or high roof
falls |
- Use a remotely operated continuous miner to remove the fallen material.
- Use a remotely operated scoop to remove the fallen material.
- Use bolters equipped with temporary roof supports that can be extended to reach high areas of the roof.
- Keep safety jacks someplace on the bolter that will prevent them from getting covered with dirt, grease, etc.
|
Marking the roof to indicate where bolts need to be
installed |
- Mount a measuring device (e.g., antenna) near the front of the bolter to help the operator line up the machine properly for the first row of bolts.
|
Unintentionally walking under unsupported roof |
- Do not leave an area of unsupported roof without posting warning devices.
- Do not rock dust an area until it has been bolted.
- Use a standardized warning device with some type of unique feature (e.g., a unique color) to warn people that they are approaching unsupported roof, and do not use this device for any other purpose (to rule out the possibility that miners might misinterpret what it means).
- Do not leave crosscuts and breakthroughs unbolted at the end of a shift; if the situation does occur, multiple warn signs should be posted.
|
Retrieving wrenches and steels that fall under unsupported
roof |
- Install a wrench holder near the bolter head.
- Use a bolt or a pole with a hook on the end to retrieve tools that fall beyond supported roof.
- Use "lock-in" wrenches that are less likely to come off unexpectedly.
- If a wrench or steel falls beyond supported roof leave it there and use another one.
|
Repositioning straps or pans that fall off as the bolter moves
forward |
- Use bolters equipped with devices that hold the straps securely in place while the bolter is moving forward.
- If a pan or strap falls beyond supported roof, leave it there and use another one.
- Use a bolt or a pole with a hook on the end to retrieve the pan or strap.
|
Scaling the roof. |
- Ask the continuous miner operator to use the cutter head of the miner to knock down loose pieces before pulling out of the cut.
|
Advancing the shuttle car or ram car operator's compartment beyond the last row of
bolts |
- Hang long warning flags from the last row of bolts to help the operators of remotely operated continuous miners judge when the car operator is beneath the last row of bolts.
- Install longer conveyors on the back of the continuous miner.
- Develop a sensor that could be placed on remotely operated continuous miners to show the operator its location with respect to the last row of bolts.
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Recommendations
It appears that mine operators currently rely primarily on threats of disciplinary action and classroom safety lectures to discourage miners from going under unsupported roof. However, several other options may also be worth pursuing. The following is a list of
suggested actions for keeping miners away from unsupported roof.
- Eliminate sources of motivation for going under unsupported roof by means of changes in equipment, work procedures, policies, etc. To accomplish this, it may be helpful to ask miners to identify situations that are likely to tempt people to work under unsupported roof, and to suggest what might be done to prevent these situations from occurring. This input could be obtained through interviews, surveys, or small group discussions.
Research suggests that many of the factors influencing miners to go under unsupported roof vary from mine to mine. Therefore, it is important that the operators of each mine perform their own assessment.
Remember to revaluate the situation at least every year or two, and whenever new equipment or work procedures are introduced to a face crew.
- Offer incentives for eliminating the precursors of going under unsupported roof. For example, miners may go under unsupported roof unintentionally because warning signs are not posted immediately after a cut of coal has been removed by the continuous miner. In such a situation, a system could be developed for randomly measuring performance on this task and tying rewards to how often the signs are missing at locations where they should have been posted.
Do not necessarily offer incentives on a continuous basis. They should be used whenever the target behaviors (or target conditions) appear to become less prevalent.
- Increase fear of the harm that roof falls can cause. Perform this action
with all new employees and as a reminder to first-time transgressors.
- Conduct behavioral modeling to show supervisors how to interact with miners who they find under unsupported roof.
Perform this action with all new section supervisors, and conduct refresher training every few years.
- Have high level managers communicate their commitment to the goal of keeping people away from unsupported roof.
Do this at least annually and whenever someone has been found violating this rule.
- Use disciplinary actions. Threaten formal action with first-time transgressors. Use formal action if a second transgression occurs. If the behavior reappears after one attempt has been made at formal punishment, the person should be quickly eliminated from working near areas of unsupported roof. If the person has other types of useful skills, offer them an inherently safe job, one that is removed from areas of unsupported roof and that is unlikely to tempt the person to perform other types of unsafe acts, e.g., a job in an office or some other safe work area aboveground.
References
- Peters, R., Fotta, B., and Mallett, L., The Influences of Seam
Height on Lost-Time Injury and Fatality Rates at Small Underground Bituminous
Coal Mines. Applied Occupational and Environmental Hygiene, 16(11),
2001, pp. 1028-1034.
- Peters, R., Strategies for Encouraging Miners to Stay Away from Unsupported Roof and Perform Self-Protective
Actions. BuMines IC 9283, 1991, 29 pp.
- Peters, R. The Challenge of Enforcing Safety Rules in Remote Hazardous Work
Areas. Professional Safety, November 1991, pp. 27-31.
- Peters, R., and R. Randolph. Miners' Views About Why People Go Under Unsupported Roof and How To Stop
Them. BuMines IC 9300, 1991, 59 pp.
- Peters, R., and W. Wiehagen. Human Factors Contributing to Groundfall Accidents in Underground Coal
Mines: Workers' Views. BuMines IC 9127, 1987, 24 pp.
- Peters, R., Miners' Views About How to Prevent People From Going
Under Unsupported Roof. In: Proceedings of Preventing Coal Mine Groundfall
Accidents: How to Identify and Respond to Geologic Hazards and Prevent
Unsafe Worker Behavior. Pittsburgh, PA: U.S. Department of the Interior,
Bureau of Mines, IC 9332, 1992, pp. 25-31.
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