Fall Occupational Safety & Health Committee Conference Monday, September 25, 2017

Portland, OR

Personal Aerosol Monitor

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Background

NiSource purchased two personal real-time aerosol monitors primarily for respirable crystalline silica monitoring - There are other potential uses and benefits that we will

discuss

This presentation summarizes experiences and lessons learned with these monitors

Top overall benefits are instantaneous results and long term ROI vs. analysis cost

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Compliance Interpretation

From OSHA RCS Final Rule Preamble: “Employers could also use portable, direct-reading instruments to accurately characterize employee exposures to respirable crystalline silica. These devices measure all respirable dusts, not only silica. But where the employer is aware of the proportion of crystalline silica in the dust, direct-reading instruments have the advantage of providing real-time monitoring results.”

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Available Instruments

I am not a paid representative of any of the manufacturers or suppliers of these monitors

This presentation describes high-tier performance and capabilities of any available models

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Principle of Operation

Photometer (Nephelometer) - Ambient air is drawn by a vacuum pump through a chamber

where aerosol is exposed to a laser - Diffractions of the laser light are read by an optical sensor - Quantifies the # of particles

Can quantify any kind of aersol including, fibers, mist, fume, dust, or fiber

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Principle of Operation (cont.)

Photometric Light Scattering - Photometers measures the amount of light scattered by the

fog - “Thicker fog” = brighter - More aerosol = higher reading

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Reference Dust / User Calibration

Photometric reference = Arizona Road Dust - AKA “A2 fine test dust” – dates back to 1940’s air filtration

industry to compare filter performance - Known refractive index, size distribution, and density - Aerosols have different shapes & sizes

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Reference Dust / User Calibration

Fly ash

Coal Dust

Concrete

Arizona Road Dust

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Reference Dust / User Calibration

Photometric calibration factor (PCF) - You will get higher accuracy if you

account for differences

- Side by side photometry & gravimetry

- Area monitoring – send to laboratory

- Must have enough aerosol present to exceed gravimetric analysis LOD

- Cal Factor = Gravimetry / Photometry • Could affect results by factor of 2 or more

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Application to Crystalline Silica

1) Obtain photometric cal factor for each major type of material

2) Set photometric cal factor on instrument - It will automatically factor into results

3) Get % crystalline silica: Bulk samples or from gravimetric & XRD air samples - Factors = Coal type / blend, unit type (cyclone vs. injection),

size & age of unit

4) Multiply respirable dust result by crystalline silica % correction factor for final result

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Limitations

Some worst-case assumptions must be made if the worker is exposed to multiple types of dust: - User cal factor (photometric) - % crystalline silica correction factor

If you do not know % crystalline silica of your materials, you must assume it is all silica - This may still be a viable option for very low risk tasks

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Limitations (cont.)

Humidity / Precipitation - Limit for reliable quantification is 95% non-condensing - Results may skew high for hygroscopic aerosol in high

humidity – zeroing instrument in field will help - Heavy rain or direct steam could damage electronics

Durability Battery life: Some models may not support extended

shift Not intrinsically safe Temperature range: 0°C - 50°C (32°F – 120°F)

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Size Selective Sampling Accessories

With no accessories in place – measures total particulate

4 size-selective impactors (@ 1.7 LPM) - 1µm, 2.5µm, 5µm, and 10µm

Dorr-Oliver Cyclone (@ 1.7 LPM) - 4µm 50% cut-point for ISO 7708

Diesel Particulate Matter (DPM) cyclone - Used to differentiate DPM from other

ambient aerosol (.8µm 50% cut-point) - MSHA DPM exposure limit

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Datalog / Data Management

55 days data log memory space (@ 1 log per minute) Manual (push to start / stop) or scheduled run modes Comes with software for data manipulation and

reporting

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Sampling & Analytical Error

Photometry (respirable dust) - Accuracy: ± 5% of reference dust - Precision: ± 2% of reading or ± 5µg/m3 (whichever is greater)

Gravimetry is a direct measurement without any form of calibration against a reference

X-ray diffraction (bulk) - Accuracy: ± 18% - Precision: ± 8%

Unknown variation: - Obtaining a “representative” photometric calibration - Pulling a “representative” bulk sample - Worker variation in personal sample

Detection Range: .001 mg/m3 to 100 mg/m3

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Calibration

Zero cal – Before each use

Cyclone flow cal (verify 1.7 LPM) - Before and after each use if cyclone is

added

Factory service

- Recommended annual recalibration and service

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Other Applications

Beryllium

Training – ventilation efficacy – welding fume & grinding

Indoor air quality dust surveys - Could compare against ASHRAE 62.1 (Ventilation for

Acceptable Indoor Air Quality)

Diesel particulate surveys

Metal working fluid (MWF) / oil mist assessments

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Questions?

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