Monday, 13 December 2010

Trussing Safety

If you look back at some of my older posts (Oct.28, 07 and Mar.16, 09), you will see my emphasis on safety and effective risk management. One of the biggest concerns for safety is in trussing. I am still amazed at the number of major trussing collapses that occur each year at special events. Here are just a few examples from YouTube that have happened in the past couple of years.

1. Christina Aguilera and Justin Timberlake Concert 2008

2. Elton John Chichen Itza Concert Stage Collapse 2010

3. Madonna Concert Stage Collapse in France 2009

4. Stage Collapse at Big Valley Jamboree in Canada, August 2009

5. Silverdome Truss Collapse 2010

6. South African Stage Trussing Collapse 2010

7. Roof System Collapse in Turkey

8. Rocklahoma Side Stages Collapse 2008

It's pretty obvious that even production teams for the most well-known stars have problems. That still is no reason to bypass the necessary equipment safety standards and procedures for safe installation of trussing used in smaller events. But we're rushing things a bit. Let's look at trussing from the beginning.

Trussing as we know it, started to develop at the end of the 1970s in response to the entertainment industry’s demand for lightweight, strong temporary structures that could span the width of a stage and be used to hang lighting and audio systems. Familiar with the spatial lattice structures found in bridges, scaffolding, and buildings, manufacturers used this as the basis for modern truss design. Today it is ubiquitous in the industry and comes in a wide variety of sizes, shapes, colors, and strengths.

Trussing must be able to withstand loads imposed on it in shear (i.e. force directed along the cross section, such as high loads on top of a vertical truss section) and in deflection (i.e. force directed down and perpendicular to its horizontal access, such as too many luminaires clamped in one position). The amount it can withstand depends of course on its size and rated load. Each type and size of truss is rated by the manufacturer for specific maximum loads under these conditions. It is therefore critical that riggers know the exact loads that will be imposed on the truss in these conditions and what the total weight of the loaded truss will be so that the correct choice of supporting wire rope cable, slings, and chain motors may be made. Not only that, but the truss supplier for an event (e.g. usually the lighting company) is obligated to understand the load rating of their truss and to choose the proper truss accordingly, knowing in detail what the loading will be before the truss is ever rigged into position.

Particularly important are unique loading scenarios encountered outdoors. These include:

  • Wind. Wind can cause damage to canopies and walls, it can overload trusses and towers due to the extra load of attached walls, and it can lift all or part of the complete structure.
  • Rain or snow. This can make trussing slippery for climbing, it can cause overloading of rooftops due to accumulation of snow or water, it can cause short-circuiting in control systems, and it can cause the support of saturated soils to weaken. 
  • Lightning. This can cause severe personal safety risk if it hits towers. 
  • Temperature. Solar heat can cause aluminum to become extremely hot, thus making it unsafe to the touch. It may also cause the safe temperature of any polyester cling covers to exceed their allowable limit. (e.g. surface temperature can reach 150 C, greater than the normal safe limit for polyester of 100 C).
It is therefore imperative that such things as roofs be constructed properly and with due consideration of the expected weather conditions. For example, the inclusion of supporting guy wires, base distance frames (to minimize compression loads), and adequate ballast is absolutely necessary. Additionally, heights of towers and roofs must be restricted to recommended maximums, both indoors and outdoors. For example, the height of a tower grid system should be no more than 6 m if the width of the outrigger tower base is 2 m (outdoors is generally three, and indoors four times the base width as a rule-of-thumb). A properly qualified rigger and the truss supplier should be able to certify compliance with these requirements.

From this it can be implied that to rig trussing at an event without using a properly qualified rigger is asking for trouble. And that goes for trussing hung indoors or roof systems that are ground-supported outdoors.

One positive recent development is the introduction of a North American, industry-wide certification program by the Entertainment Services and Technology Association (ESTA). This program, called the Entertainment Technician Certification Program (ETCP), requires that riggers pass a three-hour knowledge exam set and scored by an independent body, the Applied Measurement Professionals, Inc. There are two certification categories: ETCP Certified Rigger – Arena and ETCP Certified Rigger – Theatre. For the special event industry, the arena certification is the desired one and it is strongly recommended that producers only work with such qualified individuals.

You wouldn't want your event to end up being a disaster video on YouTube.