ZT Safety Systems have been promoting a new harness type, with many claims of reduced load and body trauma, and a reduced anxiety concerning suspension.
I have not seen any evidence concerning the claims, and confess to being surprised by some aspects within the promotional video. I have respect for the companies involved with it, however my initial thoughts are these :-
- Stability is the key criteria for compression loads, and a harness whose primary load path involves the legs will put very high compression loads into the leg joints, which are unlikely to be “aligned” during the arrest event. The selected shots from the ZT promotional video shows the legs scrunching up, but there is no time line indicated to show the pace of the event.
- The high speed video of other harness test falls that I have seen using anthropomorphic dummies, reveal significant limb movement both in the fall and in the arrest. I worry about the potential for joint damage in the legs.
- The front connection might be appropriate in limited applications like those shown in the video (some of which do not show best practice), however an arrest event from the chest connection results in unrestrained head movement, and I would like to learn how they measure this. One key benefit from the dorsal connection is that the sternum and chin limit head movement range. Many construction applications benefit from a rear attachment, and could result in a rapid body rotation during the arrest with this harness.
- When I last checked the harness EN, Harnesses were tested with a limbless timber manikin without load sensors. Load application on the body, and the load levels are therefore not measured, nor is there the opportunity to apply the harness load through the limbs.
I do not know the test regime for this harness, and will try to learn more. I would simply urge caution if considering a change.
Semi elastic conventional harnesses worn correctly, permit sufficient freedom of movement for many construction applications, without being too uncomfortable (personal experience). The “meatballs” hazard is primarily caused by poor harness selection and poor discipline in wearing. This is normally the result of the decision maker being ill informed and not personally affected by the decision (they don’t have to wear it).
I think the ZT harness is an interesting development, and it certainly seems less restricting for the user. I would be very interested to learn more.
