Published in the September 2010 Australian Longwall Magazine

Hopefully you will recall my definition of Human Error: It can result from the best intentions of a variety of people, including (but not limited to): planners, general managers, accountants, engineers (all disciplines), managers, superintendents, coordinators, supervisors, operators, consultants and original equipment manufacturers.

So if I were designing a longwall today, I would eliminate the seven deadly sins as follows:

• 1. Slothfulness

  Operating the longwall with only one hydraulic pump.

  The problem: You can have all the rules under the sun that say “never operate the longwall with only one pump” but it still happens ... and so does the ensuing bad roof as the support pressures are degraded.

  The fix? Design the pump station so that it is physically impossible to operate the longwall on less than two pumps. It is as simple as that.

  Comments: If a pump breaks down, fix the pump or have three pumps – two running and one on standby. One pump is acceptable when the longwall supports are not moving.

• 2. Complacency

  Operating the longwall supports at less than the designed setting pressures.

  The problem: Roof conditions are directly related to setting pressure. The more you reduce the set pressure, the more you damage the roof.

  The fix? Using the powered support control system, enable parameters that do not allow longwall operations at less than a predetermined system pressure. It really is simple.

  Comments: If the system pressure is lower than the predetermined limit, fix the problem. Don’t create another even bigger problem.

• 3. Inactivity

  Leaving supports back when they should and can be advanced.

  The problem: Leaving supports back reduces the effective density up to 20%.

  The fix? If a support is left back (out of sequence) I would have an annoying audible alarm on that support along with a visible warning on the Citech Screens on the surface computers.

  Comments: If the support is broken, fix it. If it is not broken, advance it.

• 4. Lack of discipline

  Bends on the longwall.

  The problem: Bends on a longwall face cause the break-off line to move in front of the rear edge of the support canopy. This means the support is trying to support the goaf. This will result in “jack knifing” and subsequent roof failure.

  The fix? Landmark.

  Comments: Inertial Navigation has arrived in style and the “ball of string’s” days are numbered.

• 5. Mismanagement of creep and horizon The problem: Being in the wrong place both vertically and horizontally relative to the coal seam. Sound familiar?

  The fix? Landmark.

  Comments: I would respectfully suggest that the cost of downtime when the maingate drive is stuck in the rib, or the cost of a roof fall after the horizon has been lost, could possibly pay for Landmark in one event.

• 6. Excess: Too big canopy ‘tip to face’ distance The problem: The bigger the tip to face, the more roof has to be supported. From a practical viewpoint, the issue is really about “pick to tip” distance especially when changes of horizon are required.

  The fix? Effective use of modern horizon control systems and Landmark (again) will overcome many of the problems associated with tip to face as well as dedicated one piece relay bars that are not adjustable.

  Comments: Most issues with tip to face arise because of telescopic relay bars. It is too easy to put the support on the back hole making the tip to face bigger, the walkway bigger and tip to pick distance bigger. All very convenient, but not good for the roof.

• 7. Lack of maintenance

  The problem: Leaks and bypasses degrade support performance but do not necessarily stop the longwall.

  The fix? The highest standards of maintenance aided by the latest software diagnostic tools. There are several packages available.

  Comments: My personal favourite is an Australian software package called LVA (Longwall Visual Analysis). Brilliant technology that is available today.

So, the future of longwall technology is actually already here, we just haven’t recognised it yet.

These simple but effective controls can save the industry millions upon millions of dollars and make the working environment significantly safer for all concerned.