Industrial hygiene in Prescott: aerospace parts and finishing shops

Manufacturing around Prescott and Prescott Valley runs to machining, aerospace parts, fabrication and finishing, with the finishing work producing most of the air hazards worth measuring. Prescott is under 2 hours from the Valley, so a survey here is a routine trip for us.

Our field is industrial hygiene, the discipline behind workplace air monitoring and noise surveys.

Aerospace parts and light manufacturing

The air hazards in these shops come from the finishing work more than from the machining:

• Hexavalent chromium comes from chromate conversion coating, chem film and chromated primers. OSHA's permissible exposure limit (PEL) is 5 micrograms per cubic meter of air (µg/m³), and the action level is 2.5 µg/m³. Sampling requires one filter type for plating and another for painting and welding.
• Isocyanates come from two-part polyurethane topcoats. They require a specially treated filter, known as a derivatizing filter, because an ordinary charcoal tube picks up nothing at all.
• Welding fume is where the manganese gap bites. OSHA's PEL for manganese is 5 milligrams per cubic meter of air (mg/m³), set in 1971, and it is a ceiling limit. ACGIH, the professional body that publishes the threshold limit values (TLVs), sets a TLV of 0.02 mg/m³ for the respirable fraction of the fume, the part fine enough to reach deep into the lungs. A shop can therefore demonstrate that it meets the PEL and still be far above the current health-based limits. The harm in question is to the nervous system.
• Metalworking fluid mist and solvent come from machining and parts cleaning.

→ Hexavalent chromium air sampling · Isocyanate air sampling · Welding fume monitoring · Metal fabrication and machine shops

One technical note about elevation

Prescott sits above 5,000 feet, and Prescott Valley and the sites around it are in similar country. Air pressure there is meaningfully lower than at sea level, which affects three things:

• The flow calibration of a sampling pump
• The cut point of a respirable cyclone, the device that separates out the fine dust
• The readings of gas monitors that use electrochemical sensors

All three respond to air density or gas pressure, not only to the concentration of a substance in the air.

The correction belongs in the calibration we do in the field, not in a spreadsheet afterward, which is why we calibrate on your site and not in Phoenix before we drive up.

We cover this in full on the Flagstaff page. The elevation is higher there and the effect is larger, but the same principle applies here.

→ Flagstaff, Arizona

Practical notes

Yavapai County does not run its own air program. In Arizona, only Maricopa, Pima and Pinal counties do. Air permits for Prescott sites therefore come from ADEQ, the Arizona Department of Environmental Quality, not from a county department.

We do not handle air permits, but a register of compliance obligations that was copied from a Phoenix plant names the wrong agency.

Facilities that file Form R, the annual federal Toxics Release Inventory (TRI) report, owe Arizona a separate Toxic Data Report through myDEQ, the state's online system, plus a pollution prevention plan. The Toxic Data Report is due the same July 1 as the federal report. Filing through TRI-MEweb, EPA's online reporting system, does not cover the state filing.

We work from one Arizona office and have no Prescott branch. Prescott is under 2 hours from the Valley, which makes a 1-to-3-day survey a simple trip and not a project.

We work in four fields here:

• Tier II chemical inventory reporting (due March 1)
• Form R / TRI reporting (due July 1)
• Air monitoring surveys and noise surveys
• ISO consulting for environmental management (ISO 14001) and for occupational health and safety (ISO 45001)

→ Where we work