Sound levels

It is a distinctive characteristic of the live performance industry that performers and support staff are critically dependent on their hearing. The focus of this guideline is sound levels encountered in rehearsals and performances, including music, sound effects, pyrotechnics, gunshots etc.

Staff involved in the construction of sets and costumes may be exposed to dangerous sound levels from power tools and other machinery. Carpenters, props builders, electricians, welders, sewers and others exposed to noise produced by saws, nail guns, compressors, sewing machines etc. should wear hearing protection. Refer to Section 139 of Regulation 851 (Industrial Establishments) under the Occupational Health and Safety Act (OHSA) for the regulatory requirements regarding hearing protection. The Construction Projects Regulations (O. Reg. 213/91) apply to load-ins, fit-ups, set-ups, lighting hangs, load-outs, tear-downs and strikes; where multiple departments are working simultaneously in the same area; where unique installation/removal techniques are in use; and where workers may be exposed to hazards from a wide variety of sources. Once the workplace is no longer a construction project, the Regulation for Industrial Establishments (Reg. 851) applies.

Hearing loss due to sound exposure is cumulative. Workers should be aware that activities at a traditional worksite, including in performance, are only a part of one’s daily work-related exposure to sound. Additional sound exposures may include personal rehearsal time practicing instruments, listening to students playing and listening to personal recording devices with headphones or earbuds.

This guideline does not address exposure outside of live performance workplaces; however, workers are encouraged to consider additional sound exposures as a contributing source of hearing loss.

The following recommendations are intended to help prevent long-term auditory damage to workers, while minimizing impact on artistic standards.

Definitions

Note: The definitions are provided for clarity and guidance only.

A-Weighting

see dBA

dB (Decibel)

A unit of measurement of sound pressure level. [Abbreviated definition. For the full definition refer to section 139(1) of Regulation 851 (Industrial Establishments) under the OHSA]

dBA

A measure of sound level in decibels when measured on the A-weighted network of a sound level meter. A-weighting uses an electronic filter that approximates the frequency response of the human ear. [Abbreviated definition. For the full definition refer to section 139(1) of Regulation 851 (Industrial Establishments) under the OHSA]

Equivalent sound exposure level (L_ex,8)

The steady sound level in dBA which, if present in a workplace for eight hours in a day, would contain the same total energy as that generated by the actual and varying sound levels to which a worker is exposed in his or her total work day, determined in accordance with a formula that takes into account the cumulative effect of sound pressure level, duration of exposure, and the exchange rate. [Abbreviated definition. For the full definition refer to section 139(1) of Regulation 851 (Industrial Establishments) under the OHSA]

Equivalent sound level (Leq)

Equivalent sound level is a measurement of sound over a specified period of time.

Exchange rate

A rate, measured in decibels, indicating when the damage done by sound exposure is doubled. A 3 dB exchange rate means that damage is doubled for every increase of 3 dB.

Hearing conservation program

A program to prevent and control noise-induced hearing loss.

Impulse sound

A percussive sound such as a gunshot or a cymbal crash. The sound is often very loud and may have peaks over 115 dB.

Loudness

Loudness is the subjective impression of the intensity that allows us to place it on a scale going from very soft to very loud, without reference to any physical scale. Within any one listening environment, there is a good correlation between the physical measure of intensity and the subjective sense of loudness, yet there can be some differences.

Personal Protective Equipment (PPE)

PPE is equipment worn to minimize exposure to a variety of hazards. (Example: hearing protection such as ear plugs or ear muffs). Although an important part of health and safety management, PPE is considered the last resort of hazard control, used only after engineering controls and administrative controls (or work practices) have been shown to be impractical, ineffective, or insufficient.

Steady state sound

Sound that does not involve a rapid rise and fall of levels, as compared to impulse sound. The sound can be loud but has a more consistent level than impulse sound (a non-varying sound, e.g. a held note on a trumpet, or the whine of a table saw).

Sound pressure level (SPL)

The intensity of sound measured in decibels.

General Guidelines

1. Employers are to take all measures reasonably necessary in the circumstances to protect workers from exposure to hazardous sound levels.
2. Employers must ensure that workers are not exposed to a sound level greater than an equivalent sound exposure level (L_ex,8) of 85 dBA (see subsection 139(6) of the Regulation for Industrial Establishments).
3. A risk assessment specific to sound level hazards should be conducted, and appropriate engineering controls and work practice decisions incorporated in advance of first need. In addition, sound level hazards should be reassessed and issues resolved during the rehearsal period and before the first performance. In determining sound level hazards, both sound pressure levels and sound exposure duration will be factors.

4. Where a worker’s noise exposure is not consistent, the following table shows maximum times for exposures. When this threshold is reached, the worker’s noise exposure has reached 100% of the maximum daily noise exposure.

    

   Table 1 – Maximum Allowable Exposure (based on the equivalent sound exposure level in section 139 of the Regulation for Industrial Establishments (Reg. 851))

   Duration	Steady Sound Level (dBA)
   8 hours	85
   4 hours	88
   2 hours	91
   1 hour	94
   30 minutes	97
   15 minutes	100

   NOTE: based on a 3 dBA exchange rate. The formula for determining the equivalent sound exposure level referred to in Table 1 can be found in Appendix B of the Amendments to Noise Requirements in the Regulations for Industrial Establishments and Oil and Gas - Offshore.

   The allowable exposure time to an equivalent sound level of 85 dBA is 8 hours (see section 139 of the Regulation for Industrial Establishments). If the equivalent sound level goes up by 3 dBA, the allowable exposure time is cut in half, to 4 hours. At 100 dBA the allowable exposure time is only 15 minutes per 8 hour workday, though we recommend no exposure to those levels without protective measures (e.g. sound baffles or hearing protection devices). Remember to include practice, teaching and research in the 8 hours.

5. Workers should not be exposed to impulse sound pressure levels in excess of 100 dBA. Where impulse sound levels above 100 dBA cannot be avoided, exposure control measures should be established to minimize the exposure. For example, when rehearsing a scene that includes a gunshot or other impulse sound which exceeds 100 dBA, all workers should be made aware of the hazard at each repetition, so that appropriate measures may be taken.
6. Employers are required to protect workers from exposure to a sound level above 85 dBA L_ex,8 by implementing 1) engineering controls and 2) work practices to reduce sound levels.
7. Using personal protective equipment (PPE) to protect workers from exposure to a sound level greater than the limit shall only occur when engineering controls:
   • are non-existent or not obtainable;
   • not reasonable or not practical to adopt, install or provide because of the duration or frequency of exposures or because of the nature of the process, operation or work;
   • rendered ineffective because of a temporary breakdown of such controls; or
   • ineffective to prevent, control or limit exposure because of an emergency.
8. A clearly visible warning sign shall be posted at every approach to an area in the workplace where the sound level regularly exceeds 85 dBA (see subsection 139(10) of the Regulation for Industrial Establishments).
   
   Note: Refer to the Amendments to Noise requirements in the Regulations for Industrial Establishments and Oil and Gas-Offshore Guideline which sets out some examples of the content the signs may include.

Assessing Noise Exposures

1. It is important to assess noise exposures to help determine what measures are necessary to ensure the health and safety of employees who are exposed to noise. The following information is a summary from the Ministry of Labour guideline which describes how to implement a noise exposure survey. Please refer to the Amendments to Noise requirements in the Regulations for Industrial Establishments and Oil and Gas-Offshore Guideline for more information.
2. A noise dosimeter, an integrating sound level meter, or in some circumstances, a basic sound level meter can be used to measure sound levels. The Canadian Standards Association provides guidance on equipment selection and specifications, and on procedures for the measurement or calculation of sound levels.
3. Compliance with Ontario’s regulatory requirements respecting noise exposure control does not necessarily mean that a comprehensive noise survey needs to be done in every workplace. Previous sound level or dosimetry data may be useful in assessing worker exposures and the likelihood of them exceeding the occupational exposure limit. Exposure data for a group of workers with the highest noise exposures may be useful to infer compliance for less exposed groups.
4. Indicators that point towards the need for a noise exposure survey include the use of equipment known to produce sound levels above 80 dBA in published data, worker complaints regarding noise and symptoms, or audiometric test results showing early signs of noise-induced hearing loss. It is appropriate for an employer to carry out a noise exposure survey using approved measurement tools when noise levels consistently exceed 85 dBA (e.g. orchestra pits).
5. Employers may contact their Safe Workplace Association or consultants specializing in noise assessments to assist them with assessing sound levels in their workplace if they do not possess the required instrumentation, resources, or knowledge to carry these out. Also, the Occupational Health Clinics for Ontario Workers has published a useful Noise Calculator spreadsheet on their website.

NOTE: Sound pressure levels should be measured at the ear of the worker most exposed to the sound source. All measurements of sound levels in the workplace should be taken at performance levels without adjusting the measurements to account for the use of PPE (e.g. hearing protection devices).

Hearing Conservation Programs

Although not required by the regulations, it is considered good health and safety practice for an employer, in consultation with the Joint Health and Safety Committee (JHSC), to implement a Hearing Conservation Program that includes audiometric testing of workers regularly working in areas with noise levels exceeding 80 dBA. This benefits both workers and employers by identifying potential gaps in the noise exposure control program.

Reference for such programs can be found at some of the links listed in the Resources section of this guideline.

1. Hearing conservation programs are the responsibility of the employer, in consultation with workers. Every employer shall take all measures reasonably necessary in the circumstances to protect workers from exposure to hazardous sound levels. (see subsection 139(3) of Reg. 851). Program components may include sound monitoring, feasible administrative and engineering controls, audiometric testing, hearing protection, worker training and education, and record keeping.
2. In hearing conservation programs for long-running productions (in excess of six months), periodic hearing assessments should be considered. The results of such assessments are the sole property of the worker and his/her audiologist.

Sound Level Reduction in Performance

The best way to reduce sound impact is to put a distance between source and worker. Even in a limited space, repositioning or re-angling the sound source can make a useful difference.

1. Speakers: Speakers and monitors should have minimal floor contact since low frequencies tend to travel through solid surfaces rather than through air. Reducing the surface contact of speakers and monitors will increase the low end frequencies received by audience and performers, so the overall sound level need not be as high. Workers should not be exposed to the backs of open speaker enclosures. Baffles between the worker and the speakers should also be used.
2. Risers: Raising the sound source 30-60 cm (1-2 ft.) above the ear of the affected worker greatly reduces high frequency sound exposure. Because high frequency sounds, typically those produced by a speaker horn or a belled musical instrument, are directional, sound pressure levels above, below or to the side of the source are significantly lower than those in front of it.
3. Spacing: Wherever possible, 2-3 m (6-8 ft.) of reflective floor surface should be left unoccupied in front of a performance group. This generates additional reflections, which raise the sound level in the audience but not on stage, so the overall level need not be as high.
4. Isolation of impulse sound: Workers should not be within 2 m (6 ft.) of an impulse sound. Wherever possible, shields and baffles should be used and reflective surfaces around the sound source should be acoustically treated to reduce the impulse effect. Where it is not possible to isolate the worker, additional measures should be used.
   
   Note: if the impulse sound is above the limit specified in the Regulation, the use of hearing protection devices (i.e. PPE) is only allowed in certain circumstances.
5. Sound baffles and acoustical shields: Baffles and plexiglass shields may give protection if used with other strategies to reduce the overall sound exposure. However, acoustical baffles afford minimal effect unless they are within 18 cm (7 in.) of the worker's head. In addition, the maximum high frequency attenuation is only about 15-17 dB.
6. Hearing protection: Uniform attenuator ear plugs are available in custom and non-custom forms. Other types of hearing protection are available for specific situations. An audiologist or other hearing health care professional should be consulted before choosing.

Conclusions

There are a number of strategies to reduce the potentially damaging effects of loud sound on hearing. Environmental alterations or modifications to the room, location of the orchestra or band, and alterations in the loudspeaker system, can all provide relief while maintaining optimal sound quality and acceptance by both performer and audience. Hearing protection, if properly specified and of uniform attenuation, can be a very useful strategy to minimize the potentially damaging effects of loud sound, both on and off the stage.

Call toll-free

Call 1-877-202-0008 anytime to report critical injuries, fatalities or work refusals. For general inquiries about workplace health and safety and to report potentially unsafe work conditions, call 8:30 a.m. – 5 p.m., Monday to Friday. In an emergency, always call 911 immediately.