Exposure to excessive noise [>85 dBA] can cause short-term (acute or reversible) or permanent hearing loss (chronic or irreversible) depending on the type of noise the employee is exposed to. Different types of work generate different types of noise.

Overexposure to noise can cause a range of auditory and non-auditory effects. Auditory effects are physiological effects that impact hearing and are those that most people think of when considering overexposure to noise. These effects include:

• Acoustic trauma - Sudden hearing damage caused by a short burst of extremely loud noise.
• Tinnitus – Ringing or buzzing in the ear.
• Temporary hearing loss - Also known as temporary threshold shift (TTS), this injury occurs immediately after exposure to a high noise level. Hearing gradually recovers over a day or two spent in a quiet place.
• Permanent hearing loss – Also known as a permanent threshold shift (PTS), it is typically the result of overexposure to noise over months or years. As the name suggests, the effects are permanent and there is no medical treatment or cure. Permanent hearing loss occurs gradually, so most people do not even realize they are experiencing PTS until it is significant enough to impair day-to-day activities.

Non-auditory effects of exposure to high noise levels include both psychological and physiological effects such as:

• Interfering with speech, concentration and thought processes.
• Disrupting sleep.
• Fatigue and aggression.
• Reduced immune response.

It is important to know that overexposure to noise does not necessarily take a long time. Short periods of very high noise can cause overexposure and irreversible damage to the ear.

The three main types of noise are distinguished by how the noise changes over time.

• Continuous noise remains constant and stable over a period of time. For example, boilers in a powerhouse, fans, vibrating machines, and compressors.
• Intermittent noise fluctuates between quiet and loud in a given time period. For example, woodworking machines and sewing machines.
• Impact or impulse noise occurs in very high intensity and very short duration. For example, punch press, hammering and gunshots.

Exposure to noise is expressed in decibels (dB), a measurement of sound pressure. Noise measures are typically reported in “dBA”, a scale where the noise measurement is ‘weighted’ or adjusted to match the variable response of human hearing to different pitches or frequencies.

Limits for noise are typically given as the maximum duration of exposure permitted for various noise levels, and are defined by two primary factors:

• Criterion level - The steady noise level permitted for a full eight-hour work shift.
• Exchange Rate - The amount that the permitted noise level may increase when the duration of exposure is halved.

Nova Scotia has adopted the threshold limit value (TLV) for continuous or intermittent noise as published by the American Conference of Governmental Industrial Hygienists (ACGIH) as the occupational exposure limit. [N.S. Reg. 52/2013, s. 2.3] Under the ACGIH TLV, the criterion level for an 8-hour exposure is 85 dBA, and the exchange rate is 3 dBA. Expressed in table format, the allowable pressure levels and times are:

Impact and impulse noise involve brief, but high-level, noise excursions that last less than a second. These sources usually result from colliding objects causing them to ‘ring”, or from explosions or other processes that form a shock wave. No exposure of an unprotected ear in excess of 140 dBC is permitted. Note that impulse noise is measured using a “C” weighted scale, which better reflects the response of the human ear to sudden impact noise than does the “A” weighted scale for continuous or intermittent noise.

The employer must:

• Make sure the workplace complies and that employees comply with above threshold limit values for exposure to noise. [N.S. Reg. 52/2013, s. 2.3]
• Adequate personal protective equipment (PPE) or devices required for the assigned task are based on: [N.S. Reg. 44/99, s. 9]
• The nature of the task
• The location and conditions of the workplace
• Any hazards that may affect the health and safety of persons in the workplace
• Employees receive training in the proper use and care of PPE or devices and follow this training when PPE or devices are required.
• According to the manufacturer’s instructions, a competent person maintains the PPE and devices, and they are tested or visually inspected before each use.
• The PPE or devices are not used until they are repaired when a person identifies any defect that may make the equipment or device inadequate.

Measures an employer may take to help ensure compliance and prevent health hazards from excessive noise exposure can include:

• Measure the noise levels and the time spent by an employee when it is suspected the employee's exposure exceeds 80 dBA. Noise monitoring data can help with deciding allowable unprotected periods of exposure and types of controls to implement to protect employees from overexposure to noise.
• When using a sound level meter to measure noise, use calculations to determine an employee's noise exposure when the employee is exposed to substantially different levels of sound during a workday. This calculation is known as the time-weighted average (TWA) exposure.
• When practical, install and use appropriate engineering controls to control the noise at the source.
• Provide hearing protective equipment to keep the exposure to noise within the allowable limits if engineering controls cannot be used to limit exposures.
• Have employees use hearing protective equipment that conforms to CSA standard CSA Z94.2-14, "Hearing protection devices - Performance, selection, care and use".
• Where noise levels exceed 85dBA, signs can be used to clearly indicate the range of the noise levels measured and warn of the noise hazard.
• Provide audiometric testing for employees exposed to noise above the TLV to determine if the control measures are effective at preventing overexposure to noise.

The employee must:

• Cooperate with your employer to ensure compliance with the threshold limit values You should follow company safety rules and procedures about noise and use engineering controls or hearing protection where applicable.
• Be trained and authorized by your employer to use protective equipment. [N.S. Reg. 44/99, s. 9(2)]
• Wear required protective equipment and make sure that all the parts are present and working correctly. [N.S. Reg. 44/99, s. 9A]
• Notify your employer of any damaged protective equipment. [N.S. Reg. 44/99, s. 9(4)]

The two main types of hearing protection are muffs and plugs which generally provide better protection.

Plugs and muffs should have a Noise Reduction Rating (NRR) printed on the packaging. This rating is the protection provided in an ideal situation. In the real world, the protection may only be half of the printed NRR and this variation needs to be considered when determining if employees are adequately protected when working in noisy environments.