The engineering calculations and construction drawings that authorize a temporary event structure to be erected are necessary but not sufficient to ensure public safety. The completed structure must be verified to conform to those documents before the audience is admitted; loads during event operation must be managed to prevent the structure from being overloaded; and an Operations Management Plan must be in place to guide the response to weather events and other emergency conditions. Together, these requirements ensure that the engineering work performed in pre-production translates into a structure that is actually safe on the day of the event.

Required Engineering Documentation

All proper temporary structure designs must include calculations to determine design forces on the structure and to establish the structural integrity and stability of the structural design. The engineer must provide: a statement about the structural system concept and what the structural system is designed to do; a list of specific critical structural items or connections that require checking by calculation prior to each erection; details of the methods of stabilizing the structure to resist all horizontal forces including rigging forces and weight distribution; and for outdoor structures, details of the methods of resisting all vertical and horizontal environmental forces such as wind (Event Safety Alliance, 2013).

Construction drawings are required for all but the simplest temporary structures. These must be accompanied by complete calculations, design loads, and any relevant test results. For structures requiring local authority permits or approvals, these documents must be submitted in compliance with the authority’s permit submission schedule rather than the start of construction schedule. Organizers should determine the permitting timeline for each event jurisdiction during the planning phase (Event Safety Alliance, 2013).

Risk Assessment

The structure provider must implement a safety plan and risk assessment specific to the design, erection, and suitability of the temporary structure for each configuration. At festival events where multiple performances use the same structure, multiple assessments may be required because the production elements, loads, and hazard profile can change between performances. Even the addition of a banner or sign can change the risk and safety plan due to the change in wind loading it introduces; a banner that adds several hundred square feet of wind-exposed surface area to a stage roof can substantially increase the overturning moment on the structure’s foundation system (Event Safety Alliance, 2013).

Supervising the Installation

All activities related to the erection and construction of temporary structures must be monitored to ensure that they are being erected to the detailed specification and that the safety plan and safe working practices are being followed. All structures must be checked by a qualified person after erection and before use to confirm conformance with drawings and specified details (Event Safety Alliance, 2013).

It is preferable to have the design engineer personally perform an evaluation of the structure prior to use at the event. A letter should be obtained from the engineer stating that the structure complies with the design intent of the engineer’s calculations and drawings. The International Building Code (Sections 1702 and 1704) describes a process of “special inspection” by a person with distinct expertise who verifies compliance with approved construction documents and referenced standards; the ESG recommends this approach as prudent practice for the owner or operator of the temporary structure (Event Safety Alliance, 2013).

This requirement — that the engineer of record determine that the as-built structure meets their design intent — is critical and frequently overlooked. Engineering documents specify a structure; the actual structure as erected in the field may differ from the design in ways that materially affect structural safety. Bolted connections that are incorrectly torqued, guy lines at incorrect angles, ballast in incorrect quantities or locations, and supplemental loads added without engineering review are all conditions that can exist in the as-built structure without being apparent from a non-engineering inspection. Only the engineer or a qualified inspector working on the engineer’s behalf can determine whether these conditions have compromised structural safety.

Before Admitting the Audience

Temporary structures must comply fully with the design documentation before the audience is admitted to the site. If modifications to the structure prove necessary, those changes must be approved by the qualified engineer and, where applicable, by the authority having jurisdiction (Event Safety Alliance, 2013). Unauthorized modifications including the addition of signs, banners, billboards, projection screens, scrims, scenic facades, additional lighting units, or speakers must not be added to temporary structures without the prior consent of the qualified engineer. Equipment loads such as lighting, special effects, sound systems, and video screens can be significant, and accurate or conservative weight data must be included in the engineer’s calculations before any equipment is attached.

A specific concern regarding flexible loads is the treatment of scrims, screens, and banners: whether these elements should be free-hanging or anchored at their bottom edge significantly affects the wind load they impose on the structure, and the engineer must specifically analyze and approve whichever condition will apply (Event Safety Alliance, 2013).

Monitoring After Erection

A competent person must continuously monitor any structure that is susceptible to the effects of weather or misuse. This person may be a representative of the structure supplier or a properly trained and qualified rigger. For structures that are unused between performances, the structure must be secured in a way that does not require constant monitoring, and a thorough evaluation must be conducted before the structure is returned to use after the secured period (Event Safety Alliance, 2013).

Load Management

Loads on temporary structures must not exceed the allowable loads considered by the engineer. During load-in, erection, dismantling, and load-out phases, particular caution is required to prevent overloading, as these phases involve movement of heavy equipment and changes to the load distribution on the structure (Event Safety Alliance, 2013). People and equipment causing overcrowding of any part of a temporary structure must be prevented; the structure’s allowable floor load rating must be communicated to all personnel who will use the structure.

Requirements for Outdoor Event Structures

The ESG’s requirements for outdoor event structures establish specific compliance documentation standards that must be met before any such structure is used at an event. The structure must be a purpose-built system used for its intended purpose. All aspects of the structure must comply with applicable local building codes and standards, including the current versions of ASCE/SEI-7 (Minimum Design Loads and Associated Criteria for Buildings and Other Structures) and ASCE/SEI-37 (Design Loads on Structures During Construction). Where building codes do not address temporary structures or impose requirements that are not suitable for temporary structures, the designer should consider utilizing the provisions of ANSI E1.21 (Entertainment Technology — Temporary Entertainment Structures) or an equivalent standard, subject to AHJ approval (Event Safety Alliance, 2013).

The event producer must submit required documentation to the artist team no later than seven days before the planned commencement of construction. Any changes, additions, or modifications to the structure or plan must be completed and submitted by three days before construction begins for engineering review. Changes after this deadline should not be accepted (Event Safety Alliance, 2013).

Letter of Conformity

Before the day of the event, compliance of the structure with applicable codes and standards must be demonstrated by providing a Letter of Conformity or Letter of Compliance. This letter must be supported by: engineering drawings including erection diagrams, plan and elevation views, and identification of all structural connections, rigging points, guy line connections, and supported loads; engineering calculations from a licensed engineer establishing allowable loads for audio, lighting, scenic, and video equipment; environmental load limits including wind and seismic; ground conditions and foundation requirements; and lateral stability and anchorage requirements (Event Safety Alliance, 2013).

The letter package must also include event-specific compliance documentation demonstrating that the structure is sufficient for the specific event loads and conditions, including a site suitability assessment, overall site layout diagram, rigging plot overlaid on the structure, applicable permit copies, and a certificate of completion from the installer upon completion of erection (Event Safety Alliance, 2013).

The Operations Management Plan

An Operations Management Plan (OMP) is a required component of the documentation for outdoor event structures. The OMP describes the various operating conditions the structure may encounter and the actions to be taken when each condition is met, including regular and emergency maintenance, overloading, wind, rain, snow, ice, hail, lightning, flood, and fire (Event Safety Alliance, 2013).

Wind monitoring is addressed in specific operational terms. A specific qualified individual responsible for monitoring on-site and forecast conditions must be identified before the event. Wind must be monitored on site using an anemometer or other appropriate device; relying solely on remote weather service data without on-site measurement is insufficient. A reliable means of communication must be established with appropriate weather resources to monitor impending conditions. The OMP must identify specific actions to be taken at specific reported or forecast wind speeds; these threshold speeds must be set with the understanding that removal of equipment must be done in safe wind conditions, which are typically well below the design threshold wind speed (Event Safety Alliance, 2013).

Similar load thresholds and action plans must be established for all potential environmental hazards, not only wind. Snow accumulation, ice formation, hail, lightning, and heavy rain all affect temporary structure safety and must be addressed in the OMP. The IBC and ASCE/SEI-7 provide the relevant design loads for these conditions.

Responsibility and Chain of Command

The OMP must identify individuals responsible for specific tasks before the event begins. Required identified roles include the weather monitor, stage manager, security personnel, artist’s representative, promoter’s representative, and the temporary structure vendor’s crew lead. All individuals in the chain of command must be aware of their immediate supervisor, and contact information including names, phone numbers, and work locations must be provided before the event (Event Safety Alliance, 2013).

Event Suspension and Cancellation Authority

Any entity with definitive responsibility for a portion of the event — including the temporary structure vendor, production manager, promoter, or state or local authority — has the authority and in some circumstances the non-negotiable responsibility to suspend or cancel an event if public safety is jeopardized. The method of initiating an event suspension or cancellation must be outlined explicitly before the event so that responsibilities and liabilities are identified and the decision, when made, can take effect immediately (Event Safety Alliance, 2013).

The OMP must also address response time constraints. Key questions include: how long does it take to fully evacuate a maximum-capacity audience; and how long does it take to bring critical equipment to a less vulnerable state such as landing flown audio systems? Knowing these parameters allows the command team to set decision deadlines that ensure timely responses to developing conditions, rather than discovering during an emergency that the available response time is shorter than the time required to complete the necessary actions safely (Event Safety Alliance, 2013).

Conclusion

The documentation, monitoring, and operational management requirements for temporary event structures represent the bridge between engineering design and operational safety. An engineered structure that is poorly erected, overloaded, inadequately monitored, or managed by personnel who do not know their responsibilities when conditions deteriorate provides less protection than the engineering implies. The Letter of Conformity, Operations Management Plan, and the clear delineation of suspension authority are the operational mechanisms that translate structural engineering work into actual public safety. Events at which these mechanisms are absent or incomplete have experienced catastrophic structural failures with fatal consequences; their implementation is a fundamental obligation of responsible event production.

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.

International Code Council. (2021). International building code, Sections 1702 and 1704: Special inspections. ICC.

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