Task-Specific Hazards and Accidents

Crane, Derrick, and Hoist Hazards

Moving large, heavy loads is crucial to today's manufacturing and construction industries. Much technology has been developed for these operations, including careful training and extensive workplace precautions. There are significant safety issues to be considered, both for the operators of the diverse "lifting" devices, and for workers in proximity to them.

This module is a starting point for finding information about these devices, including elevators and conveyors, and their operation.

The derrickman on a well drilling operation performs his tasks from various elevated work platforms in the mast. He is exposed to falls when not using fall protection equipment while climbing the derrick ladder, while working with the pipe stands, and while moving from the ladder to his platform station. The derrickman is also exposed to crushing injuries from shifting stands of pipe and elevator latching tasks.

Adequate and continuous fall protection is a prerequisite for the safety of employees working on a derrick. Conditions beyond the control of the derrickman (wind, vibration, pipe movement) make even momentary unprotected exposures hazardous.

Crane, Derrick, and Hoist Hazards (Continued)

The primary functions of the hoisting apparatus are to:

• raise and lower the drill string components during tripping and drill stem lengthening operations,and
• to support the drill string at the desired bit weight during drilling.

The drawworks is essentially a rotating spool, usually located on the drill deck, controlled by a clutch and brake system operated by the driller. The wire rope drill line runs from the drawworks to the crown block at the top of the derrick, and then to the traveling block and hook, which is attached to the drill string during drilling operations. The drilling line diameter and reeving sequence of the blocks are determined by maximum drill string weight. The deadline anchor, usually located on the derrick substructure, serves as an adjustable terminal anchor point for the wire rope. Typically, the dead line anchor will be adjustable to allow for the continual addition of new wire rope to the hoisting system.

Employee exposure to hazards associated with hoisting should be slight unless structural defects exist or system overloading occurs. Routine inspection of elevated hoist mechanisms involves the risk of falls. Pinched fingers and injuries from wire rope splinters are other hazards.

Materials Handling Hazards

On a drill rig, most of the materials handling equipment are unique to the oil field. This equipment is used in the working routines of raising and lowering the drill string, adding new sections of drill pipe, and tripping. The most common type of accident that occurs in materials handling operations is the "caught between" situation (e.g.; when a load is being handled and a finger or toe gets caught between two objects.)

The requirement for material handling creates many hazards, including:

• Overexertion Injuries - Workers directly involved in these operations are close to moving equipment components, while performing tasks that require substantial exertion and good coordination between individuals.
• Crush Injuries - Transferring drill pipe from the rack to the drilling platform may result in the stockpile rolling or in the mishandling of suspended loads, with the risk of crushing injury.
• Fall to Same Surface Injuries - Rolling stock (drill pipe and collars) can shift and/or fall from a pipe rack or truckbed. Employees must be alert to the hazards attendant to pipe handling and racking.
• Struck-by Objects - Vertical and near-vertical storage of drill pipe on the inclined ramp requires adequate slippage protection and employee procedural training for safe handling.
• Fall to Below Injuries - Improper rigging of loads can result in load shifts and objects falling on those below. Materials handling is a support activity, so safe materials handling procedures frequently are not given the necessary emphasis.

Materials Handling Hazards (Continued)

• Poor Posture Injuries - Handling of the tongs requires well-coordinated efforts and proper body limb placement.
• Caught-in Injuries - Mistakes in the hands-on spinning chain operations can lead to entanglement that may result in crushing, amputation, and death.
• Contact-with Injuries - Machinery is activated by an operator who depends on visual and/or audible cues; a mistake can lead to premature activation while workers are still in contact with moving parts.
• Unexpected startup/shutdown - Mechanical failure from overloading systems can occur.
• Slips, Trips, Falls - Lifting and moving heavy items on wet surfaces may lead to slips, falls, and overexertion.
• Eye Injuries - Eyes are at risk from material falling off the drill pipe.

Potential hazards in these operations can be increased if the drilling crew has not worked together very long; teamwork is necessary to carry out the operations quickly and safely.

Catastrophic Events

Catastrophic accidents involve the destruction of the drilling rig and/or injuries to multiple employees.

Blowouts, derrick collapse, and hydrogen sulfide accidents are included in this category.

Even though these accidents frequently may involve loss of life as well as the major destruction of equipment, the actual number of casualties represents only a small percentage of the total occupational injury incidence and severity rates in well drilling.

Blowouts

A blowout is an uncontrolled flow of gas, oil, or other well fluids occurring when formation pressure exceeds the pressure applied to it by the column of drilling fluid.

Blowouts may occur when the formation fluid pressure exceeds the hydrostatic pressure of the circulating fluid in the well annulus such as the totally unexpected encountering of unpredictable pressures and/or when mechanical controlling methods (e.g., blowout preventers (BOP's) or other pressure-control techniques) fail through misuse, misapplication, or malfunction. During a drilling operation, the mud serves as the first control method.

Most wells are drilled in oil fields with predictable formation pressures. BOP's selected to be compatible with these pressures are installed as soon as the surface casing is in place. BOP's function by sealing off the well bore. A series of hydraulic (and some manual) rams activated from ground level (not on the derrick) seal and contain the formation pressures.

A kick is the entry of water, gas, oil, or other formation fluid into the well bore. It occurs because the pressure exerted by the column of drilling fluid is not great enough to overcome the pressure exerted by the fluids in the formation drilled. If prompt action is not taken to control the kick or kill the well, a blowout will occur.

If the kick is not noticed in time or the techniques used to control the formation pressures are not adequate, then a blowout occurs. Since blowouts and subsequent fires involve the loss of equipment and time (as well as employee exposure to extremely hazardous conditions), the industry usually takes great care to prevent their occurrences.

Derrick Collapse

Although not a common occurrence, derrick or mast collapse most frequently happens during rigging-up and rigging-down procedures.

• The greatest strains are exerted on the mast components during these operations.
• Derrick frames subjected to abuse during movement may be damaged and wrecked.
• Inspection of the derrick structure is important for the detection of weld weakness, oxidation, and bent members.
• Weight indicators and recorders allow the driller to stay within mast load tolerances; consequently, they must be maintained and inspected.
• Manufacturers' rig capacities and guying requirements should always be followed.

Hydrogen Sulfide Accidents

Hydrogen Sulfide gas is very corrosive and causes metals to become brittle. Therefore, employers need to take special precautions when choosing equipment when they may reasonably expect to encounter H2S.

This may include appropriate H2S trimming of equipment in accordance with National Association of Corrosion Engineers (NACE) Standards. We will cover more on Hydrogen Sulfide safety later in the course.

Video

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