Task Planning for Dredging with Clamshell

This common procedure may not always receive the safety planning it deserves.

• By William Johnston
• Feb 01, 2005

IN the construction industry, we often deal with new or unique situations. Because they are unusual or new, we tend to plan more intently to ensure the work goes safely. But repetitive work also needs to be carefully planned because that is where most manhours are spent and the most hazards exist from a long-term point of view. Dredging with clamshells is one of those repetitive, very common procedures that may not always receive the safety planning it deserves.

Clamshells, and the cranes that operate them, present numerous potential dangers as well as opportunities for proper safety planning. A clamshell dredge bucket system involves a single bucket, the crane, and the cables used to operate the clamshell. The dredge operates by lifting the bucket, dropping it into the bottom of the sediment, lifting the bucket and dredged material to the surface, and emptying the material into its storage/destination. To help ensure that risks in clamshell operations are identified and mitigated, task planning has proven to be a reliable safety tool.

When working with any type of equipment, it is critical that a thorough pre-use inspection be performed. It is also just as critical that task planning take place.

Proper task planning helps to ensure that:

• Everyone involved in the work activity is aware of what the team is doing.
• Each individual is aware of his/her responsibility.
• The correct tools and equipment are available.
• Potential hazards are identified and mitigated.
<>I>Work activity steps are identified and communicated.

Task planning is as important when performing repetitive tasks as it is for new or unique tasks. When performing repetitive tasks, it is easy to overlook the small or simple elements and focus on the more complex. For instance, we might overlook "minor" equipment maintenance issues in order to focus on the location of our spoils pile. That oversight could lead to equipment failure and damage or, more important, to injury of an employee.

To help avoid that type of oversight, have a task plan to perform both scheduled and non-scheduled maintenance. Clamshell dredging is a duty cycle process and will require more frequent planned maintenance. This will allow you to be prepared at all times and help to eliminate surprises; it also prevents overlooking of maintenance while focusing on other areas of the work, such as the spoils pile.

Task planning consists of four critical elements:

• 1. Identifying the individual steps to completing a task.
• 2. Identifying the key equipment/tools needed for each step.
• 3. Identifying the potential hazardous exposures for each step.
• 4. Identifying mitigations for each potential hazardous exposure.

Following are several items to consider during the development of a task plan for clamshell dredging operations.

Condition of equipment:
--Is the crane the right size and type for the operation?
--Have the crane and components been properly inspected?
--Has the clamshell bucket been properly sized and inspected?
--What potential hazards were found during inspection of the equipment?
--Is all required equipment documentation current and available?

Equipment setup:
--How stable and level is the surface area upon which the crane and the clamshell, and other associated equipment, will be set?
--What size equipment mats are needed?
--Have measures been taken to prevent the bucket from opening while unloading/loading?
--Are there structures (buildings, trees, electrical lines or poles, bridges, pipes, etc.) that have the potential to contact any part of the crane or its attachments during operation (think 360s)?
--Has personnel access to the swing area and load travel path been closed and properly barricaded so nobody will be under a load?
--Have all equipment, materials and other items that could be damaged by a falling load been moved out of the swing area and travel path or otherwise been protected?
--Are there vibrations from other sources (local traffic, work operations, etc.) that may pose a potential settling or tipping hazard to the equipment or clamshell bucket while set stationary or during operation?

Scheduled and unscheduled maintenance:
--Is time scheduled to inspect and service the boom, wire rope, and sheaves of the crane at least twice per shift and the bucket pins, arms, teeth, sheaves, and ropes even more often?
--Have the area and equipment been identified so the bucket can be blocked, secured, and prevented from opening while being serviced?
--Has the "Jack line," or closing line, been prepared in advance to be replaced on a regular basis prior to its breaking?
--How will the bucket be kept secured in the event of a wire rope or pin failure?

Protection of the public and other workers:
--Is the public protected from access to the work site?
--Are other workers able to maintain a safe distance from the clamshell operations?
--Has the spoil removal process been set up to limit exposure to other workers and the public?

This is certainly not a complete list of items to consider when developing a task plan for dredging operations, but it may motivate some thought. Each dredging operation, no matter how routine it appears, offers its own unique hazards. By consistently taking the time to plan properly, you can exponentially reduce the opportunity for incidents to occur.

This article appeared in the February 2005 issue of Occupational Health & Safety.

This article originally appeared in the February 2005 issue of Occupational Health & Safety.