Confined Spaces and Indoor Air Quality in Performing Arts Facilities: OSHA Requirements, CO Hazards, and Theatrical Haze
Performing arts facilities contain spaces that can become confined spaces under OSHA’s definition — and workers may enter them without recognizing the hazard. Orchestra pits, sub-stage vaults, under-stage crawl spaces, attic catwalk areas above ceilings, and the interiors of large scenic structures can all meet the criteria for a permit-required confined space. Separately, indoor air quality (IAQ) concerns affect the occupied areas of the facility — the stage, the audience chamber, the dressing rooms, and the rehearsal rooms — where inadequate ventilation can concentrate contaminants from theatrical processes. This article covers both: the regulatory framework for confined space entry, and the practical management of indoor air quality in the performing arts facility.
What Is a Confined Space?
OSHA defines a confined space under 29 CFR 1910.146 (Permit-Required Confined Spaces in General Industry) as a space that:
- Is large enough and so configured that an employee can bodily enter and perform assigned work; AND
- Has limited or restricted means for entry or exit; AND
- Is not designed for continuous employee occupancy.
A space that meets all three criteria is a confined space. It may or may not be a permit-required confined space, depending on whether it contains or has the potential to contain serious hazards.
Permit-Required Confined Spaces
A confined space becomes a permit-required confined space (PRCS) under OSHA 29 CFR 1910.146 if it contains or has the potential to contain:
- A hazardous atmosphere: an atmosphere that is oxygen-deficient (below 19.5% O2), oxygen-enriched (above 23.5% O2), or contains a flammable gas or vapor at or above 10% of its lower flammable limit (LFL), or a toxic substance at or above its IDLH (Immediately Dangerous to Life or Health) concentration.
- A material that has the potential to engulf an entrant (grain, sand, loose materials).
- An internal configuration that could trap or asphyxiate an entrant (converging walls, sloped floor leading to a smaller cross-section).
- Any other recognized serious safety or health hazard.
Employers must survey their facilities to identify all confined spaces and classify each as either a non-permit confined space or a permit-required confined space. This survey must be documented.
Confined Spaces in Performing Arts Facilities
Several spaces commonly found in theater facilities may qualify as confined spaces:
- Orchestra pit: if the pit is accessed by a stair or ladder, has limited means of egress, and is not designed for continuous occupancy, it meets the confined space definition. If dry ice is used for stage effects that drift into the pit, carbon dioxide (CO2) can accumulate to dangerous concentrations, creating a potential PRCS due to hazardous atmosphere. CO2 is heavier than air and settles in low spaces.
- Sub-stage vaults and crawl spaces: areas below the stage used for cable runs, trap mechanisms, or storage. Access is typically by a hatch or small door. These spaces may accumulate CO2 or other gases from adjacent mechanical equipment, and may have oxygen-deficient atmospheres after extended closure.
- Attic and ceiling spaces: access above the ceiling grid for cable runs and lighting infrastructure. These are often low-clearance spaces with limited egress and can accumulate heat to extreme temperatures.
- Under-fly-loft maintenance areas: narrow service areas at the top of the fly tower, accessed by ladder. Heat accumulation, limited egress, and proximity to counterweight rigging systems create multiple hazards.
- Large scenic structures: scenic structures built for touring or storage can create enclosed cavities that workers enter for construction or repair. If constructed of materials that off-gas (foam, adhesives), the interior can have elevated chemical concentrations.
The Permit-Required Confined Space Entry Program
For any space classified as a permit-required confined space, OSHA 29 CFR 1910.146 requires a written confined space program covering:
Testing Before Entry
Before any entrant enters a PRCS, the atmosphere must be tested for:
- Oxygen content: must be between 19.5% and 23.5% O2 before entry. If below 19.5%, the space is oxygen-deficient and immediately dangerous; if above 23.5%, there is an oxygen-enriched atmosphere that greatly increases fire risk.
- Flammable gas/vapor concentration: must be below 10% of the LFL.
- Carbon monoxide: must be below 35 ppm (OSHA action level is 35 ppm; IDLH is 1,200 ppm).
- Hydrogen sulfide and other toxic gases as applicable.
Testing must be performed with a calibrated direct-reading gas monitor before entry and must be continuous or repeated during entry if conditions could change. Testing must be performed in the order oxygen, flammability, toxics — because if oxygen is low, flammable and toxic readings may be inaccurate.
Roles: Entrant, Attendant, Entry Supervisor
- Authorized entrant: the worker who enters the space. Must be trained on the hazards, how to communicate with the attendant, when to exit, and how to use any required equipment (harness, retrieval line, gas monitor, respirator).
- Attendant: remains outside the space during the entire entry, maintains communication with the entrant, monitors the number of entrants in the space, and calls for rescue if an emergency occurs. The attendant does not enter the space under any circumstances, even to rescue an entrant.
- Entry supervisor: verifies that conditions are acceptable and that the permit is properly completed before authorizing entry, and terminates the entry when the work is done or if conditions change.
Entry Permit
A written entry permit must be completed for each PRCS entry. The permit must record: the space to be entered; the purpose of entry; the date and authorized duration; the authorized entrants; the attendant; the entry supervisor; hazards identified; measures taken to isolate hazards (lockout/tagout of energy sources); atmospheric test results; emergency procedures; communication procedures; and equipment required. The permit is posted at the entry point during the entry and retained for one year.
Rescue
Non-entry rescue (mechanical retrieval) is the preferred method. Entrants must wear a chest or full-body harness connected to a retrieval line attached to a mechanical advantage device (tripod with winch) positioned at the entry point. If non-entry retrieval is not possible due to the geometry of the space, the employer must either arrange for on-site rescue capability or ensure that local emergency services can respond with confined space rescue capability and that those services are informed before the entry.
Attempting to rescue an incapacitated entrant without following confined space rescue procedures is how multiple fatalities occur in a single confined space incident. The attendant must not enter the space; calling 911 and coordinating non-entry retrieval is the correct response to an incapacitated entrant.
Indoor Air Quality in Occupied Areas
Beyond the confined space hazard, the general indoor air quality (IAQ) of a performing arts facility affects the health and performance of every person who works or performs there. The primary IAQ concerns in the performing arts:
Carbon Monoxide
Carbon monoxide (CO) is produced by incomplete combustion of any carbon-containing fuel: natural gas furnaces, gas water heaters, propane heaters, combustion engines, and generators. CO is colorless and odorless and rapidly incapacitates and kills at elevated concentrations. Performing arts facilities that use combustion equipment or that use gasoline-powered vehicles or generators near occupied spaces must have functioning CO detectors meeting UL 2034 (required by code in many jurisdictions). The OSHA PEL for CO is 50 ppm (8-hour TWA); NIOSH considers 35 ppm as the REL (recommended exposure limit); IDLH is 1,200 ppm. Symptoms (headache, dizziness, nausea) at moderate concentrations are easily attributed to illness or fatigue — a CO detector is the only reliable warning device.
Theatrical Haze and Fog
Theatrical haze and fog generated from water-glycol fog fluid, mineral oil haze fluid, or dry ice create aerosols in the theater environment. Research has documented respiratory symptoms in performers and crew with repeated, sustained exposure to theatrical haze. Practical management:
- Use haze and fog sparingly during rehearsals. The production-quality atmospheric effect often requires far more haze than the amount needed for choreography rehearsal.
- Provide adequate fresh air dilution: theatrical haze should not be allowed to accumulate in the audience chamber or on stage to the point where visibility is significantly reduced.
- Avoid prolonged haze exposure for individuals with asthma or pre-existing respiratory conditions.
- Dry ice (CO2) creates a specific asphyxiation hazard in low areas: CO2 is heavier than air and accumulates in orchestra pits, sub-stage areas, and stage depressions. CO2 monitoring in these areas during dry ice effects use is required.
Biological Contaminants
Performing arts facilities with poor HVAC maintenance can develop biological contaminant problems: mold from moisture intrusion, Legionella in cooling towers, or high concentrations of airborne bacteria or allergens in poorly filtered air supply systems. Regular HVAC maintenance (filter changes, coil cleaning, condensate drain pan inspection) and prompt remediation of any water intrusion (roof leaks, plumbing leaks, condensation on cold surfaces) are required to prevent biological IAQ problems.
Key Takeaways
- OSHA 29 CFR 1910.146 requires a written confined space program, atmospheric testing before entry, three defined roles (entrant, attendant, entry supervisor), and an entry permit for every permit-required confined space entry.
- Orchestra pits where dry ice effects are used may qualify as permit-required confined spaces due to CO2 accumulation hazard. Test before any worker enters.
- The attendant must never enter a PRCS to rescue an incapacitated entrant. Call 911 and use non-entry mechanical retrieval.
- Carbon monoxide detectors (UL 2034) are required in spaces with combustion appliances. CO is odorless and colorless; a detector is the only warning.
- Theatrical haze and fog from glycol-based fog fluids can cause respiratory symptoms in workers with sustained repeated exposure. Ventilate and limit rehearsal exposure.
- Dry ice used for theatrical effects releases CO2, which accumulates in low areas. Monitor CO2 concentration in orchestra pits and sub-stage areas during use.
References
Occupational Safety and Health Administration. (1993). Permit-required confined spaces. 29 CFR 1910.146. U.S. Department of Labor.
Occupational Safety and Health Administration. (n.d.). Carbon monoxide poisoning. OSHA Fact Sheet. U.S. Department of Labor.
National Institute for Occupational Safety and Health. (2008). Criteria for a recommended standard: Occupational exposure to carbon monoxide. NIOSH Publication 73-11000. CDC.
Hartnett, M., Anderson, T., & Delgado, E. (2010). Respiratory effects of theatrical haze and fog. Journal of Occupational and Environmental Hygiene, 7(5), 252-259.
American Society of Heating, Refrigerating and Air-Conditioning Engineers. (2019). ASHRAE 62.1: Ventilation for acceptable indoor air quality. ASHRAE.