Semi-automatic twist locks (SATLs) are essential devices used to secure shipping containers during transport and hoisting operations when loading and unloading container vessels. However, SATLs occasionally fail to operate properly, posing serious risks to longshore workers tasked with freeing stuck or jammed locks. This article explores the hazards of inoperable SATLs, analyzes key factors contributing to SATL failures, and offers best practices to safely address inoperable locks in marine terminals.

The Dangers of Inoperable SATLs

As outlined in the OSHA fact sheet, defective or improperly installed SATLs have directly contributed to numerous severe and fatal injuries amongst longshore workers attempting to manually free stuck locks. When SATLs fail, workers are often forced into dangerous positions between containers and surrounding structures in efforts to manually release the jammed locks. Sudden uncontrolled container movements during these operations have resulted in workers being fatally crushed or struck.

Several disturbing real-world examples highlighted in the document demonstrate the immense risks workers undertake when dealing with stuck SATLs:

  • A foreman was killed after attempting to manually hold open a SATL while the attached container was hoisted. The container broke free, swung violently, and crushed the foreman against a handrail.
  • A lasher was killed after an upper container secured by improperly installed SATLs broke free from the lower container during a tandem lift. The releasing container dropped directly onto the worker below.
  • A lasher manipulating an inoperable SATL was fatally struck after the SATL unexpectedly gave way, causing the container to swing uncontrollably into the worker.

These sobering examples clearly showcase the potential consequences of improper SATL operations. When SATLs fail to operate as designed, workers can be exposed to crushing hazards, falling container hazards, swinging container hazards, and pinch point hazards in their efforts to manually free the locks. As the provided document stresses, inoperable SATLs represent an extremely hazardous condition necessitating cautious control procedures to mitigate risks.

Causes of Inoperable SATLs

According to the OSHA guidance, common causes of SATL failures include:

  • Broken or damaged unlocking pigtails, preventing manual or remote unlocking
  • Container corner casting damage or distortion from rough cargo handling, jamming the SATL
  • Improper upside-down installations of the SATL
  • Internal corrosion and component failures from extended saltwater exposure
  • Overstressing and damaging of internal SATL components from use

Any of the above factors can result in non-functional SATLs requiring manual worker intervention to separate locked containers. Without proper precautions, these manual SATL operations endanger workers to the grave hazards previously highlighted.

Best Practices for Inoperable SATL Operations

When facing inoperable SATLs, maritime employers and workers must implement stringent controls and procedures to safely conduct manual separating operations. Core guiding principles include:

  • Ensure proper supervision of all SATL operations, with emphasis on hazard recognition and risk mitigation
  • Provide extensive training to SATL operators on recognition and safe manipulation procedures
  • Institute fall protection, safe lifting protocols, danger zone controls, and proper PPE
  • Safely access inoperable SATLs without walking directly on container tops
  • Maintain continuous communication between supervisors, workers, and crane operators
  • Utilize specialized tools designed to force open stuck SATLs when possible
  • Remove defective and damaged SATLs from service until repairs are completed

By putting such control measures in place and optimizing awareness, communication, and SATL operation best practices, the risks associated with stuck container locks can be significantly reduced. But as a last resort, more hazardous manual measures may be required after all other options have been exhausted.

Techniques of Last Resort

If initial attempts to free an inoperable SATL fail, maritime employers may be forced to implement risky procedures referred to as “methods of last resort” in the document. Two such techniques include:

  1. Emergency Container Relocation All container locks may need to be re-secured before slowly moving the stacked containers to the nearest safe location for further SATL access. This delicate operation requires extensive coordination and hazard controls to prevent catastrophic separation and swinging if the defective SATL unexpectedly fails during the lift.
  2. In Situ SATL Destruction
    As an absolute last ditch resort, the inoperable SATL may need to be physically cut out or burned off while still installed between containers. This demands tremendous care to avoid corner casting damage which could compromise structural container integrity. Similar to the emergency relocation method, extreme hazard controls are vital given the innate risks associated with this SATL removal technique.

When executed judiciously under ideal supervision and communication, these last resort methods offer a final option to mitigate inoperable SATL incidents. But their extremely hazardous nature demands that they only be activated once all other options have been exhausted.


In closing, defective or jammed SATLs continue to pose severe injury and fatality risks to longshore workers tasked with manually freeing stuck container locks. Only through persistent adherence to SATL operation best practices, early problem SATL identification, robust operator training, and ultra-cautious conduct during hazardous last resort procedures can maritime entities hope to eliminate accidents associated with inoperable container locks. This complex challenge persists as an occupational risk factor inherent to intermodal freight handling across the global integrated transportation network.