The Vital Role of Lockout/Tagout, Blockout, and Testout Procedures
A crucial element of a conveyor safety program is the lockout/tagout procedure. In the United States, lockout/tagout is mandated by the Occupational Safety and Health Administration (OSHA), while the Mine Safety and Health Administration (MSHA) has adopted a similar rule. To ensure complete safety in dealing with the potential energy stored in belt tension or elevated bulk materials, it is recommended to also implement blockout and testout procedures.
The lockout/tagout rules stipulate that the power to the conveyor system (and any accessory equipment) must be shut down, locked, and tagged by the worker performing maintenance on the system. Only the person who applied the lockout can remove it, preventing accidental startup of the conveyor belt while maintenance is ongoing.
The typical lockout/tagout procedures include:
- Own lock: Each worker must place their own lock on the de-energized switch or switches, which may involve using one or multiple lock bars.
- Own key: The employee who installs the lock is the only one with the key to that lock and is solely responsible for its removal.
- Multiple locks: In areas where multiple employees are working, each should apply a lock to the power source. Some equipment may have several locations requiring lockout.
- Own tag: Alongside the lock, each employee should attach a tag with their name and contact details.
Three important elements of conveyor safety are proper training, guarding, and policies and procedures.
Blockout Procedures
Even after proper lockout/tagout procedures are followed, significant tension or potential energy may still be present in the conveyor system. For instance, if an inclined belt undergoes an emergency shutdown with material loaded on it, the weight of the material can cause the belt to roll backwards. This movement poses a risk of injury from both the belt's motion and potential material cascading off the conveyor.
Attempts to release these tensions by lifting the gravity take-up’s counterweight may not always be effective and should not be relied upon. Properly installed brakes and backstops can mitigate rollbacks, but they alone cannot prevent belt movement caused by internal tensions due to belt stretch.
Other factors such as blocked chutes, trapped material at load zones, material under the belt, or faulty bearings can also create sufficient belt tension. The belt may move in either direction depending on the conditions at the time of maintenance, which can evolve as work progresses.
If employees need to work on or near the belt's pinch points, the belt should be physically prevented from moving under its own power, a practice known as "blocking" the conveyor belt or blockout. Belt clamps, chains, and ratchet lever hoists (comealongs) can be used to secure the belt to a structural conveyor member capable of withstanding the forces involved.
It is advisable to use engineered equipment designed to securely clamp onto the belt to prevent unintended movement.
Testout Procedures
A testout procedure serves as a final verification that the system is securely de-energized before work resumes. It is recommended to attempt to start the belt conveyor or any interlocked equipment after the lockout has been applied. This test should include both local start/stop stations and the system’s remote controls to ensure that the correct breakers were successfully de-energized.