Anti-Two-Block Devices and Safety Systems Flashcards
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Read the first 7 Anti-Two-Block Devices and Safety Systems flashcards as text
On a crane with multiple part-of-line configurations, the A2B device must be:
Answer: Capable of functioning correctly regardless of the number of parts of line
The A2B system must protect against two-blocking in all reeving configurations used on that crane.
What immediate danger does two-blocking create for the wire rope?
Answer: The rope can be pulled over the sheave causing catastrophic failure
When two-blocking occurs, continued hoisting pulls the rope over or through the sheave, causing sudden rope failure and uncontrolled load drop.
An A2B device must interrupt which crane functions when activated?
Answer: At minimum, hoist up and boom up and telescope out functions
ASME B30.5 requires A2B devices to interrupt hoist-up, boom-up, and boom-extension functions since each of these can worsen a two-block condition.
Which condition can DEFEAT a weight-actuated A2B switch even when it is mechanically intact?
Answer: Wind blowing the hanging bob-weight sideways causing it to contact the boom
Strong wind can deflect the hanging bob-weight into contact with the boom structure, falsely triggering the A2B switch and halting operations.
When a crane is equipped with a fly jib (boom extension), the A2B device must:
Answer: Protect both the main boom tip and the fly jib tip sheaves
Separate A2B protection is required at the fly jib tip because the hook block can two-block against the fly jib sheaves independently of the main boom.
Under OSHA 1926.1416, if a required safety device such as an A2B system is not functioning, the crane:
Answer: Must be immediately removed from service
OSHA 1926.1416(d)(1) requires that any crane with a malfunctioning safety device be removed from service until repaired.
The A2B device's electrical circuit is typically designed as:
Answer: Normally closed — tripping the circuit opens it and cuts power to controlled functions
A normally closed (fail-safe) circuit design means any break in the circuit — whether from triggering or wire failure — cuts power to the hoisting functions.