Noise Dosimeter Placement
Noise dosimeter placement involves positioning the microphone in the worker's 'hearing zone'—typically on the collar or top/outside edge of the shoulder on the side of greatest noise exposure—to accurately represent sound at the ear during work. This ensures compliance with standards like OSHA's 2-foot sphere around the head and WorkSafeBC's requirement for placement within 0.5 meters of the ear, with the microphone unobstructed and oriented upward.
On a manufacturing shop floor, noise dosimeter placement is critical for accurate exposure assessment. The dosimeter body is secured to the worker's belt or pocket, while the microphone is clipped to the collar or shoulder on the side facing dominant noise sources (e.g., grinders, presses). Placement must be within the hearing zone (within 0.5 m of the ear per WorkSafeBC, or OSHA's 2-foot sphere) and unobstructed by clothing, hair, or PPE. The microphone is oriented upward or parallel to the shoulder plane per ANSI. For workers wearing respirator hoods, the microphone may be placed inside the hood if justified. Regular checks ensure the microphone remains correctly positioned throughout the shift, avoiding direct air streams from pneumatic tools that could cause wind noise.
- Microphone not in the true hearing zone: Placing it on a hat brim, chest, or lower torso instead of the collar/shoulder near the ear, leading to under- or overestimation of exposure.
- Microphone obstructed or shielded: Covered by jackets, high collars, or long hair, causing artificially low readings and failure to identify overexposures.
- Incorrect side, orientation, or task representation: Placing the microphone on the quiet side or pointing it downward, or sampling only during non-representative periods, leading to systematic underestimation of dose.
How do WorkSafeBC expectations on dosimeter placement align with OSHA and ANSI?
WorkSafeBC requires the microphone in the hearing zone, clipped to the collar or shoulder on the noisier side, within 0.5 m of the ear. OSHA defines the hearing zone as a 2-foot sphere around the head, with the microphone on the shoulder in that zone. ANSI S12.19 specifies the middle-top of the most exposed shoulder, oriented parallel to the shoulder plane. These frameworks are compatible: compliance involves microphone on the collar/top of the more-exposed shoulder, within the hearing zone, and oriented per manufacturer/ANSI guidance.
When would you deviate from standard shoulder/collar placement (e.g., respirator hoods, face shields, helmets)?
OSHA allows placing the microphone inside a respirator hood to measure actual exposure inside the hood, provided hood attenuation is consistent and documented. For helmets or face shields without full enclosure, standard placement outside PPE is used, with hearing protection evaluated separately. Any deviation must be justified in the survey plan and described in records, indicating whether it represents inside-hood or ambient exposure.
Does placement differ for area sampling vs. personal dosimetry?
Yes. Personal dosimetry involves the worker wearing the microphone in the hearing zone, capturing time-weighted exposure during tasks. Area measurements use a sound level meter microphone positioned near the employee's head (e.g., 1.5 m above floor for standing) or on a tripod at the unoccupied worker position, but this is not equivalent to personal dosimetry for regulatory compliance. Measurements must be tagged correctly as 'personal dosimetry' or 'area SLM' in records.