Industrial hygiene in Casa Grande: under Pinal County's air program

Casa Grande plants answer to an air agency that is neither the Phoenix one nor the Tucson one. Pinal County runs its own air program, which changes who issues your air permit and who inspects you against it.

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

Pinal County, not ADEQ and not Maricopa

Arizona has exactly three county air agencies with this authority: Maricopa, Pima and Pinal. Everywhere else in the state, air permits come from ADEQ, the Arizona Department of Environmental Quality.

Casa Grande is in Pinal County, so air permits for most sources go through the Pinal County Air Quality Control District. A company with sites in Phoenix and Casa Grande has two county air agencies. Add a Tucson site and it has three, plus the state for any site outside those counties. Many companies keep a compliance obligations register, the list of laws and rules they must follow, and a register that says “ADEQ” and stops is wrong in three ways.

The county line is not the whole test, though. Arizona law keeps ADEQ in charge of some sources statewide, inside the three counties as well as outside them, and portable sources are among them. In Pinal County, then, a portable crusher or screening plant gets its permit from ADEQ, not from the county, under ADEQ's Crushing and Screening Plant General Permit.

Parts of Pinal County are also in nonattainment for PM10, which means they do not meet the federal air standard for dust particles. That status brings requirements to control fugitive dust on haul roads, unpaved yards, stockpiles and earthmoving. Large industrial sites tend to get caught by this when they expand, not when they get a permit.

We do not handle air permits or dust rules, but we mention them here so that your register is accurate.

→ How to build a compliance obligations register

Vehicle and battery manufacturing

Casa Grande's heavy manufacturing includes vehicle assembly, along with battery and electric vehicle supply chain work. That base is smaller in 2026 than it was 2 years ago. Assembly jobs in the area were cut back during 2026, when a second shift came off the line and contractor jobs went with it. One nearby electric vehicle plant has stopped altogether. This is not a growth story right now.

The work that is still running has the same serious hazards it always had, and a plant on one shift instead of two owes the same air monitoring on the same processes. With a smaller crew, the people who remain usually cover more tasks. Exposure monitoring sorts workers into similar exposure groups (workers who do the same job the same way), so when people cover more tasks, each group has to represent more, not less.

Body and frame work brings welding fume, and with it the manganese gap. OSHA's permissible exposure limit (PEL) for manganese is 5 milligrams per cubic meter of air (mg/m³), set in 1971. It is a ceiling limit, a level that must not be exceeded at any time.

ACGIH, the professional body that publishes the threshold limit values (TLVs), sets its TLV at 0.02 mg/m³ for the respirable fraction of the fume, the part fine enough to reach deep into the lungs. A plant can therefore prove it meets the law and still be far above the current health-based limits. The health effect in question is damage to the nervous system.

Other welding work adds more. Gas metal arc welding on aluminum (often called MIG welding) adds ozone and nitrogen dioxide, and galvanized metal adds zinc and metal fume fever.

Paint and sealer work brings isocyanates, which come from two-part polyurethane and from structural adhesives. One technical point decides whether your data is worth anything. Isocyanates occur in a simple form (free monomer) and a larger, linked form (oligomer), and most of the isocyanate in a modern coating is oligomer, not free monomer. A report that measures monomer alone has measured a fraction of what the person applying the coating inhaled.

Sampling requires a derivatizing filter, which is a chemically treated filter. The analytical method NIOSH 5525 uses a filter coated with a reagent called MAP and measures both monomer and oligomer. An ordinary charcoal tube collects nothing.

Cell and pack work, where it runs, adds its own list. NMP, a solvent used in electrode coating, has no OSHA PEL. ACGIH sets 10 parts per million (ppm) and adds a skin notation, a warning that the chemical can be absorbed through the skin. It also notes a concern about harm to an unborn child.

Then comes the one that surprises people. The electrolyte in these cells (LiPF₆) breaks down into hydrogen fluoride when moisture is present. Hydrogen fluoride can therefore show up in a plant whose chemical inventory has no acid on it. Filling, formation, leak checks and any overheating event can release it.

→ Welding fume monitoring · Isocyanate air sampling · Battery manufacturing · Automotive plants and shops

Farming, and the hazard in the lagoon

Pinal County's farms run to cotton, alfalfa, grain and dairy, and the dairies bring a hazard that is often fatal and often underestimated.

Manure lagoons and slurry pits generate hydrogen sulfide gas, and agitating them is the critical moment. Agitation releases in minutes what built up over months.

For general industry, OSHA's Table Z-2 gives hydrogen sulfide no 8-hour time-weighted average (TWA) limit at all. It sets two other limits:

• A ceiling of 20 ppm, which OSHA calls the acceptable ceiling.
• A peak of 50 ppm for 10 minutes, once per shift, only if no other measurable exposure occurs.

You may have seen other figures in circulation: a 10 ppm 8-hour TWA and a 15 ppm short-term exposure limit (STEL). The first is a construction limit, and the second is a Cal/OSHA limit from California's state program. Neither is federal general industry law.

Hydrogen sulfide also dulls the sense of smell, so the odor fades as the concentration becomes dangerous. A plan that relies on “we would smell it” relies on the gas's most dangerous property.

Grain and feed handling brings the other side:

• Grain dust, with a PEL of 10 mg/m³ in OSHA's Table Z-1
• OSHA's standard for grain handling facilities
• Combustible dust, meaning dust that can catch fire or explode. OSHA has no general standard for it and enforces it through the General Duty Clause, the law's catch-all duty to keep a workplace free of known serious hazards.

→ Hydrogen sulfide monitoring · Respirable dust monitoring · Food and beverage plants

Where we are, and what we do here

We work from one Arizona office, with no branch here. Casa Grande is on I-10, though, roughly 50 minutes from Phoenix and just over an hour from Tucson, which makes it one of the easier places in the state for us to reach.

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