Many events require temporary structures: grandstands and seating platforms, stages and roof systems, scaffolding and access towers, tent and membrane structures, lighting and delay tower systems, and a range of smaller platforms, barriers, and fencing installations. The failure of any temporary structure, no matter how small, in a crowded and confined space can have devastating consequences (Event Safety Alliance, 2013). The collapse of stage roof systems at events including the Indiana State Fair in 2011 and the Ottawa Bluesfest in 2011 killed and injured workers and audience members, and each incident demonstrated that the risk of structural failure at live events is not theoretical but a recurring and preventable hazard.

The safety of temporary structures depends primarily on four factors: the choice of appropriate design and materials; correct positioning; proper planning and control of work practices; and careful inspection of the finished product (Event Safety Alliance, 2013). Each of these factors requires deliberate action before any structure is erected.

Legal Requirements and Organizer Responsibility

It is the organizer’s responsibility to understand and implement the relevant local, state, and national requirements as required by the authorities having jurisdiction (AHJ) for the event site (Event Safety Alliance, 2013). This responsibility cannot be assigned to the structure supplier or the engineer of record without the organizer retaining accountability. Where permits are required for temporary structures, the organizer must identify the permitting authority, understand the permit submission timeline, and initiate the process early enough to accommodate the authority’s review schedule. Many jurisdictions require structural submissions two to four weeks or more before construction begins; discovering this requirement after the timeline has passed creates both legal exposure and schedule risk for the event.

The Americans with Disabilities Act of 1990 may apply to temporary event structures to the extent that they constitute facilities open to the public. The ADA Standards for Accessible Design and the accessible stadiums guidance apply requirements for accessible routes, viewing areas, seating, and egress. Organizers and venue managers should familiarize themselves with these requirements and consult competent legal counsel to determine the specific applicability to their event’s structures. Chapter 11 of the ESG addresses ADA compliance at events in detail.

Choosing the Site Location

Many factors influence the appropriate location for temporary structures. The ESG identifies the following site evaluation criteria (Event Safety Alliance, 2013):

Site drainage must be assessed before structure placement. A site that is prone to flooding can experience reduced ground load-bearing capacity or undermining of structural supports due to water saturation or erosion. Measures to control these effects, such as drainage improvements, elevated base plates, or elevated stage decking, must be implemented before the event.

Site grade is directly relevant to structure design. Temporary structures are generally designed for level installation; where the ground is not level or is uneven, the structure must be capable of modification to accommodate grade variations, and the structural engineer must evaluate the effects of any inclination on the structure’s load-carrying capacity and stability.

Overhead power lines are a life-safety hazard in the vicinity of any structure installation, particularly where cranes are used for assembly. The required clearance distance from power lines must be verified with the serving utility before work begins. OSHA’s minimum approach distances for unqualified persons near overhead power lines are the floor, not a target.

Wind exposure and prevailing weather patterns are critical site factors for stage and roof structures. The stage should be located to reduce hazards from potential weather events; structures placed in wind corridors or on exposed hilltops face substantially greater wind loading than those in sheltered locations, and the engineering design must reflect the actual site exposure condition.

Site geometry must accommodate the full complement of event infrastructure: trucks, power generators, fuel storage, and support equipment must have sufficient space to operate without creating obstructions or hazards. The placement of lighting, sound, and video equipment relative to audience areas and egress routes also requires evaluation during site selection.

Ground load-bearing capacity must be confirmed for the specific loads that will be imposed. For outdoor events, the ground’s load-bearing capacity must be sufficient for all imposed loads in all weather conditions. Some sites have subsurface voids, utility tunnels, buried utilities, or other underground conditions that reduce load-bearing capacity at specific locations. High point loads from cranes and lift trucks used during structure assembly require specific evaluation by an engineer or qualified person (Event Safety Alliance, 2013).

Choosing the Structure

The event organizer bears the responsibility to specify the requirements of the structure, including structural performance requirements, site limitations, equipment access requirements, design intent, and anticipated event duration. Establishing these requirements typically requires consultation with the artist, venue, production suppliers, labor providers, and authorities having jurisdiction (Event Safety Alliance, 2013). Under-specification of structural requirements is a common source of structural safety deficiencies: a structure designed for a specific maximum rigging load, wind speed, or crowd density may be dangerously inadequate if any of those design parameters is exceeded during the event.

Choosing a Competent Supplier

A competent structure supplier must be able to demonstrate: a knowledge and understanding of the work involved; the ability to manage and mitigate the risks of constructing the type of structure required; the ability to provide suitable engineering documentation, including drawings and calculations; compliance with the applicable guidelines; and employment of a suitably trained workforce (Event Safety Alliance, 2013).

The ESG specifically notes that the design and engineering of temporary structures is generally outside of mainstream civil and structural engineering and is considered a specialized field (Event Safety Alliance, 2013). The design and engineering of temporary event structures should be carried out only by qualified individuals with documented experience in the design of that specific type of structure. A professional engineer with extensive experience in permanent building construction may not have the specialized knowledge required to properly design a temporary concert stage roof system, temporary grandstand, or tent structure for an event site. Organizers should verify that the engineer retained for their event’s structures has documented experience with the specific structure type and configuration involved.

Essential Design Requirements

All temporary structures must possess strength and stability, both in service and during construction, consistent with the structure’s intended purpose and requirements (Event Safety Alliance, 2013). This requirement encompasses not only the static loads imposed during normal event operation but also the dynamic loads from wind, the loads imposed during assembly and disassembly, and the effects of any changes in load configuration that occur during the event lifecycle.

The design of any temporary structure must provide protection against falls during all phases of use, including erection, operation, and dismantling. Guardrails should be provided for all stage areas, platforms, and access ways. The required guardrail height is governed by applicable local, state, or federal regulations; under OSHA construction standards and most building codes, guardrails must be a minimum of 42 inches in height. Surface conditions on ramps and treads require specific attention, particularly where surfaces may become wet during outdoor events; anti-slip surfaces, drainage, and adequate lighting are required considerations for all elevated walking surfaces (Event Safety Alliance, 2013).

Erection Requirements

The assembly of temporary structures must be carried out in accordance with calculations, plans, and specifications provided by a qualified designer or engineer. It is recommended that final design documents bear the seal and signature of a licensed professional engineer (Event Safety Alliance, 2013). An engineer’s seal on design documents is not merely a formality; it represents the engineer’s professional judgment that the design is safe and in compliance with applicable codes and standards, and it creates a defined point of accountability for the structural design.

Apparent similarities between proprietary temporary structure systems may be superficial rather than structural. Components from different manufacturers that appear physically interchangeable may have different material specifications, connection geometry, or load ratings that make them incompatible in combined use. When components from different manufacturers are used together in a single structural system, written approval must be obtained from each manufacturer and reviewed by a qualified engineer (Event Safety Alliance, 2013). The use of unapproved mixed components has been a contributing factor in multiple temporary structure failures.

Structure erection must proceed in a way that ensures stability throughout the erection process, not only at completion. Many temporary structures cannot be assembled without climbing the framework as it is erected; these conditions must be addressed in the risk assessment and safety method statement. PPE, including personal fall arrest equipment, must be used any time workers are at a working surface more than six feet above the floor. Equipment must be inspected to confirm it is fit for purpose; structural steel or aluminum elements with cracked welds, bent or buckled members, or significant corrosion must be rejected and replaced. Components must not be bent, distorted, or otherwise altered to force them to fit (Event Safety Alliance, 2013).

Connections and Hardware

Particular attention must be given to fastenings and connections throughout the structure. The connections between structural elements are the locations at which structural failures most commonly initiate; under-specified, improperly assembled, or worn connections that appear visually acceptable may be structurally deficient. Bolts and fittings that project into or adjoin audience areas must be provided with suitable protection to prevent injury from contact. Structural components must not pose a hazard or risk to the audience (Event Safety Alliance, 2013).

Conclusion

The selection of an appropriate site, a qualified structure supplier, and a design that meets applicable codes and standards are the foundational decisions that determine the safety of a temporary event structure throughout its lifecycle. Each decision requires the involvement of qualified professionals, including licensed professional engineers with demonstrated experience in temporary structure design, and each must be made with sufficient lead time to allow for permit submission, engineering review, and supplier preparation. The consequences of inadequate temporary structures are acute and have been demonstrated repeatedly at events; the standards and practices described in this article are the direct result of those incidents.

References

Event Safety Alliance. (2013). The event safety guide (version 1.1). ESA. https://eventsafetyalliance.org

American Society of Civil Engineers. (2022). ASCE/SEI 7: Minimum design loads and associated criteria for buildings and other structures. ASCE.

American Society of Civil Engineers. (2015). ASCE/SEI 37: Design loads on structures during construction. ASCE.

Entertainment Services and Technology Association. (2013). ANSI E1.21: Entertainment technology — temporary entertainment structures. ESTA.

Occupational Safety and Health Administration. (n.d.). 29 CFR 1926.501: Duty to have fall protection. OSHA. https://www.osha.gov