Selection of the preferred arrangements to be used will depend on a number of factors such as:
1.
The extent of helideck use whilst the vessel is under way
2.
The degree of exposure to marine crew when they are working on a foredeck helideck area in heavy seas
3.
Exposure during routine activities (other than helicopter operations) taking place on the vessel / helideck for instance when rigging up and towing streamers on seismic vessels.
9.10.6 Construction and Inspection Considerations
The netting should be adequately supported and fixed around the perimeter of the frame(s) and have a good hammock effect, regardless of the selected mesh material.
Polypropylene netting should ideally be supported on all sides of a panel with a substantial stainless steel wire (plastic covered) threaded through the net mesh. The netting should either be wrapped or tied to the support wire at approximately 100 mm intervals.
Wire mesh net specification and fixings should be as noted in Figure 9.11 above. Wire mesh should be secured at the outer edges with the wire ‘tails’ turned back to ensure mesh integrity is fully maintained.
There are several important things to look for when designing or inspecting the perimeter safety net.
The example in Figure 9.12 includes the following acceptable and unacceptable features:
1.
Perimeter safety net (polypropylene type) showing a good hammock effect and no supports intruding into the netting that might cause an injury when restraining an individual. ACCEPTABLE.
2.
The support angle is significantly less than 10°. This suggests the net will probably provide only limited outboard restraint for an individual falling onto it. UNACCEPTABLE.
(Photo courtesy of John Burt Associates Limited)
3. The left hand NDB Aerial Support is, in this case, causing a 5:1 Infringement within the 180° 5:1 falling gradient. UNACCEPTABLE.
This support must be modified so that the support drops straight down within the slope of the falling gradient over the edge of the safety net.
Where a support cannot be immediately modified it will be declared as an infringement in the HLL and may lead to onerous operating restrictions, particularly on take-off.
4. The NDB Aerial Support is raised above the helideck support frame.
This is generally an acceptable arrangement (a practical solution) on an existing helideck and will be needed in order to retrieve the loop aerial for maintenance.
The preferred solution on a new build or during a major helideck re-work is to position the aerial supports inboard of the net and between the perimeter net frames. When laid down the supports should be below perimeter net level.
Other unsatisfactory Safety Net features the designer should be aware of are:
1.
Mesh panel stretched too taut.
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