Audio Visual Equipment Safety in the Performing Arts
Audio and visual equipment in the performing arts involves heavy overhead loads, high-voltage amplifier racks, acoustic energy capable of causing permanent hearing loss, and increasingly complex network-based control systems. The knowledge required to work with this equipment safely spans structural rigging, electrical safety, occupational noise, and radio frequency management.
Speaker Systems and Overhead Rigging
Large-format speaker systems, including line arrays, conventional clusters, and delays, are frequently suspended over audiences and performers. A single line array element may weigh 100 to 200 pounds. A complete hung system can weigh several thousand pounds. The rigging requirements for aerial audio systems are identical in principle to those for scenery:
- All rigging hardware must be rated for the applied load. ASME B30.26 governs shackles, turnbuckles, and rigging hardware.
- A safety cable independent of the primary rigging must be attached to each speaker element or cluster.
- The weight of the complete system must be calculated and verified against the structural capacity of the suspension points.
- All suspension points must be evaluated by a structural engineer or verified against documented structural load ratings before use.
- Hang points in theatrical facilities that are designed for lighting equipment may not be rated for the concentrated loads of large speaker systems.
Line Array Assembly
Line array systems are assembled progressively, typically from the bottom element upward, while the system is on the ground, and then flown as a complete assembly. Safe assembly procedure requires:
- Following the manufacturer’s assembly sequence exactly.
- Verifying the center of gravity of the fully assembled array before attempting to fly it.
- Using a ground support or bridle configuration that matches the system’s rigging attachment points.
- Testing all inter-element connections and safety latches before lifting.
- Having a certified rigger supervise or perform the fly operation.
Amplifier Rack Safety
Amplifier racks for large-format sound systems can draw substantial power: a rack of amplifiers for a large touring production may require 200 amperes or more per phase at 208/240 volts. Key safety considerations:
- Rack power must be calculated by a qualified person and connected only to circuits of adequate ampacity.
- Cooling airflow (typically front-to-back through amplifiers) must not be obstructed. Rack doors must be open during operation or the rack must be designed for closed-door operation with adequate ventilation.
- The inrush current at system power-on can be several times the running current. Sequential power-on using a power sequencer reduces inrush current stress on the supply circuits.
- All rack equipment must be properly grounded to the equipment grounding conductor. Ground loops create noise in audio systems and are a temptation to “cheat” grounds: lifting equipment grounds in audio systems is illegal and potentially fatal.
Occupational Noise Exposure
OSHA 29 CFR 1910.95 establishes permissible noise exposure limits for workers. The 8-hour time-weighted average (TWA) permissible exposure limit is 90 dBA. The action level (which triggers audiometric testing, training, and hearing protection programs) is 85 dBA. Sound levels in front-of-house mixing positions, monitor mixing positions, and near stage monitor wedges during rock and contemporary music productions routinely exceed both of these levels.
A hearing conservation program is required by 29 CFR 1910.95 for workers exposed at or above the action level (85 dBA TWA). The program must include:
- Noise exposure monitoring to determine which workers are exposed at or above the action level.
- Audiometric testing (baseline and annual).
- Hearing protection devices provided and worn when engineering controls cannot reduce exposure below the action level.
- Training on the effects of noise and the use and maintenance of hearing protection.
- Recordkeeping of all exposure measurements and audiometric test results.
Electronic hearing protectors with pass-through amplification and level-limiting allow sound engineers to monitor audio at safe levels while protecting against high-level transients and sustained loud passages. These devices are an appropriate engineering and PPE solution for professionals who must monitor audio while maintaining hearing health.
Video Projection and LED Walls
High-intensity video projectors and LED wall systems present their own hazard profile:
- High-wattage projectors generate significant heat. Lamp compartments reach extreme temperatures. Lamp replacement must follow the manufacturer’s cool-down procedure and use appropriate PPE.
- The light output of high-intensity projectors can cause temporary or permanent eye damage if looked into directly at close range. This is particularly a concern during focus operations.
- Large LED walls may weigh several tons when assembled. Structural support requirements must be engineered.
- LED wall power distribution involves large quantities of 48VDC and 5VDC power supplies: while lower voltage than conventional AC distribution, the current is extremely high and short-circuit hazards are real.
Projector and Display Rigging
Overhead projectors, video screens, and LED panels must meet the same rigging standards as any other overhead theatrical equipment: rated hardware, safety cables independent of primary rigging, and structural verification of suspension points. The specific consideration for projectors is that their center of gravity may be at an unexpected location relative to the rigging attachment points, requiring careful balancing during initial hanging.
Radio Frequency Coordination
In-ear monitor (IEM) systems and wireless microphone systems operate in licensed radio frequency bands. Interference between wireless systems and between wireless systems and other electronic equipment is a technical problem that can also be a safety concern: a monitor engineer who cannot hear a critical cue through a failing IEM system may not be able to respond to a stage emergency in time. Frequency coordination, using software such as Wireless Workbench (Shure) or WWB6, should be performed before every production to minimize interference risk.
Key Takeaways
- Speaker system rigging must meet the same hardware and safety cable standards as theatrical scenery rigging.
- Amplifier rack power must be calculated by a qualified person. Lifting equipment grounds in audio systems is illegal and dangerous.
- OSHA 29 CFR 1910.95 requires a hearing conservation program for workers exposed at or above 85 dBA TWA.
- Electronic hearing protection with level-limiting is available and appropriate for audio professionals.
- Overhead video systems require structural engineering review and rated rigging hardware with safety cables.
References
Occupational Safety and Health Administration. (n.d.). Occupational noise exposure. 29 CFR 1910.95. U.S. Department of Labor.
National Institute for Occupational Safety and Health. (1998). Criteria for a recommended standard: Occupational noise exposure. DHHS (NIOSH) Publication No. 98-126. https://www.cdc.gov/niosh
American Society of Mechanical Engineers. (2021). ASME B30.26: Rigging hardware. ASME.
National Fire Protection Association. (2023). NFPA 70: National electrical code. NFPA.