Incident involving a McKissick N419 snatch block

IMCA recently received notification of an incident involving a particular type of snatch block, which could be knocked apart if the bolt and hairpin were removed and the block left open in an unloaded condition. In the incident described to IMCA, a component part had been knocked free and dropped from a height.

Correspondence between IMCA and the manufacturer showed that blocks produced prior to 1991 allowed removal of the head fitting, albeit after removal of the hairpin and bolt and rotation of the head fitting to an extreme position. Blocks produced since 1991 have a feature that requires a deliberate component removal to allow the head fitting to be removed when the block is open. There is a possibility that old, pre-1991 versions of the block are still in use.

We have subsequently received a third-party notice which gives the following additional information and guidance for its own operations which members may find of use:

The N419 'old style'
The N419 ‘Old Style’ was designed to allow interchangeable fittings as can be seen in the above photograph. The design utilised a ‘triangle’ shaped spool that allowed the head fitting to be rotated to an extreme position and removed after the side plate has been opened.
Current N419
The head fitting on the current N419 McKissick Snatch Block is secured to the block with a threaded round nut that is staked to the spool. This feature prevents the head fitting from being removed from the block, regardless of the position.

The company involved has banned the use at its worksites of the McKissick N419 Snatch block in figure A, whose design allowed for interchangeable head fittings as depicted in figure A.

The Crosby Group Inc. (manufacturer of the McKissick N419) has since 1991 added features to retain the head fitting regardless of the position of the block (Figure B). Both snatch blocks carry the same name, but production of the snatch block in figure A was discontinued in 1991.

As a result the company will not use the ‘old style’ snatch block (figure A) in its operations.

The company instigated the following actions for all of its installations:

  • Check all snatch blocks on installations, and remove from service the ‘old style’ McKissick N419 snatch block;
  • For applications where this type of device is required, ensure that the current Mckissick N419 snatch block is used (Figure B);
  • Make sure that all inventory lists of loose lifting appliances are updated with necessary information