Industrial hygiene analysis: evaluation method
Industrial hygiene monitoring involves various types of measuring and sampling in the workplace. OSHA’s Technical Manual guides industrial hygienists to monitor both equipment and contaminants in the workplace.
This manual includes analysis and evaluation methods that can be used to quantify industrial hygiene parameters of concern, such as chemical or particulate exposure, vibration, radiation, and noise. Here is a brief overview.
Technical equipment: On-site measurements
Direct-reading or real-time instruments or monitors provide information at the time of sampling, thus enabling rapid decision-making. These instruments can often provide the trained and experienced user the capability to determine if site personnel are exposed to airborne conditions exceeding instantaneous (ceiling or peak) exposure limits for specific hazardous air contaminants.
Gas, Oxygen, and Explosibility (Combustible Gas) Monitors
Single, dual, or multi-gas monitors can measure oxygen, carbon dioxide, carbon monoxide, hydrogen sulfide, and other toxic gases. Sample concentrations will display in ppm (part per million), percent oxygen, or percent LEL (Lower Explosive Limit).
Combustible gas meters measure flammable gas concentration as a percentage of the LEL of the calibrated gas. Note: LEL values for most flammable gases and vapors are a few percent in the air (i.e., tens of thousands of ppm) and are NOT appropriate for assessing PEL (Permissible Exposure Limit) concentrations of flammable, toxic gases.
Aerosol photometers or nephelometers are instruments used to monitor particulate matter such as dust, smoke, mists, and fumes. These instruments detect scattered light or infrared radiation. Some models can be used for monitoring the respirable fraction of dust, reported in μg/m3 or mg/m3.
Condensation nuclei counters take particles too small to be easily detected, enlarge them to a detectable size, and then count them; this device can be used for quantitative respirator fit-testing and testing the removal efficiency of HEPA (high-efficiency particulate air) filters.
There is a wide variety of commercially available detector tubes that can measure over 200 organic and inorganic gases and vapors in the air. These consist of sealed glass tubes filled with a granular material coated with an appropriate indicator chemical that will react with a particular gas or vapor to give a color change.
This color change is compared either to a scale printed on the tube or a reference chart included with the tube kit to determine the airborne concentration.
Human response to vibration is dependent on several factors. A complete assessment of exposure to vibration requires the measurement of acceleration in well-defined directions, frequencies, and duration of exposure. The vibration will generally be measured along three (x, y, and z) axes.
Typical vibration measurement systems include a device (accelerometer) to sense the vibration, a recorder, a frequency analyzer, a frequency-weighing network (gives a single number as a measure of exposure, expressed in m/s2), and a display such as a meter, printer, or recorder.
Hand-arm vibration will generally be measured when using a hand-held power tool. Measurement of whole-body vibration is essential when measuring vibration from large pieces of machinery operated in a seated, standing, or reclined posture.
The ISO standards 5349-1 and 2631-1 have been used to set TLVs (Threshold Limit Values) used by the American Conference of Governmental Industrial Hygienists (ACGIH) as OSHA does not have standards concerning vibration exposure.
Heat Stress Instrumentation
Heat stress monitors can be one of two types: a real-time area measuring environmental conditions contributing to heat stress or a real-time personal monitor that measures the wearer’s body temperature and heart rate.
Area monitors take measurements of ambient, wet bulb, and globe temperature to consider humidity and radiant heat. Personal monitors can be programmed to alarm when a predetermined temperature or heart rate is exceeded.
Nonionizing Radiation Monitors
Radiofrequency (RF) survey meters are used to measure radiation from both electric and magnetic fields. Meters can determine spatial and temporal averaging for multiple frequencies and display measurement results in percent of exposure.
Personal RF monitors can also be worn to measure individual exposure and continuously log and provide exposure results using a shaped frequency response.
Personal sampling for air contaminants
First, identify processes/operations being run, tasks performed, materials used, materials employees are exposed to, work practices used, exposure controls in place, and how effective they appear.
For active sampling, filter cassettes, sorbent tubes, and sampling pumps are attached to the employees’ clothing and used to monitor contaminant levels. For passive sampling, diffusive samplers can be used to sample gases and vapors without using a pump.
Choose the individuals to be sampled that are likely to have the highest workplace exposures (i.e., highest-risk employees) due to the materials and processes with which they work, the conditions in which they work (e.g., distance to exposure source and air movement), the tasks performed, the frequency of the tasks, and how they perform the tasks (e.g., work habits and employee mobility).
Surface contaminants, skin exposure, biological monitoring, and other analyses
Surface wipe sampling is conducted to assess a contaminant’s presence on surfaces in the workplace (such as a hazardous liquid, particles, or dried residue) that workers may contact.
Surfaces with contamination could potentially lead to either skin exposure or transfer to food and accidental ingestion. In instances where surface contamination is suspected, and the employer has not required the use of effective PPE for workers in these areas, wipe sampling may be an effective means of documenting that a skin hazard exists.
In areas where exposures to toxic metals such as lead (Pb) occur, wipe sampling of settled dust can demonstrate that potential exposure exists, and resuspension of settled dust can lead to inhalation exposure.
Sound-measuring instruments include sound level meters, noise dosimeters, and octave band analyzers. Sound level meters help identify and evaluate individual noise sources for abatement purposes.
Octave band analyzers can be used to help determine the feasibility of controls for individual noise sources for abatement purposes and to evaluate whether hearing protectors provide adequate protection. Noise dosimeters measure sound levels and are worn by workers to determine the personal noise dose during the work shift or sampling period. An average of the noise exposure is calculated over time.
The results show a TWA (time-weighted average) exposure or a percentage of the Permissible Exposure Limit.