Air Quality for Construction Sites

A reference for site safety managers, general contractor superintendents, and outdoor-crew supervisors. Covers OSHA respirable particulate standards, the Cal/OSHA wildfire smoke rule (the only state-level outdoor-worker smoke regulation in the U.S. as of 2026), AQI-based action thresholds, and respirator selection for site use.

The regulatory landscape

For outdoor construction crews, two regulatory regimes apply to ambient air quality:

• Federal OSHA sets a Permissible Exposure Limit (PEL) for respirable particulate not otherwise regulated (PNOR) of 5 mg/m³ (5,000 µg/m³) as an 8-hour TWA — a level that is orders of magnitude higher than any ambient outdoor AQI scenario. Federal OSHA does not have a wildfire-smoke-specific outdoor worker standard.
• Cal/OSHA Section 5141.1 (effective 2019, revised 2023) is the only state-level outdoor wildfire smoke standard. It triggers at AQI 151 (Unhealthy for PM2.5) and requires employers to implement engineering controls, administrative controls, and provide respirators (at minimum N95s) for outdoor workers exposed for more than one hour during a shift.

Washington, Oregon, and Colorado have all studied adopting similar rules; as of May 2026 none have a finalized regulation. If you operate in California, the Cal/OSHA rule is enforceable; everywhere else, an internal policy is voluntary but increasingly expected by GCs, owners, and insurers.

Recommended AQI thresholds for outdoor crews

Building on the Cal/OSHA framework, a reasonable cross-jurisdictional internal policy:

Respirator selection

For PM2.5 (wildfire smoke, dust): N95 is the workhorse. A properly fitted N95 filters ≥95% of particles 0.3 µm and larger; fit is the variable that matters most. A leaky N95 can effectively perform like a surgical mask.

For prolonged exposure or higher concentrations, P100 (or half-face elastomeric with P100 cartridges) raises filtration to 99.97% and tolerates beard stubble better than a disposable N95 — though Cal/OSHA still requires a clean-shaven seal for fit-testing.

Important caveat: N95s do not filter ozone, NO₂, SO₂, or other gases. If your AQI is being driven by ozone (common on hot summer afternoons in industrial corridors), the right control is to shift work to early-morning hours, not to issue masks.

Wildfire smoke playbook

For sites in or downwind of fire-prone regions:

• Before fire season: stock N95s in the site trailer (budget ~$0.50/each in bulk); confirm everyone has documented fit-testing on file; brief crews on the AQI thresholds in your site safety plan.
• During a smoke event: assign one person to check AQI hourly. The AirNow Fire & Smoke Map (and apps that pull from it, including Smog Report) is the authoritative source. PurpleAir citizen sensors are also useful at the neighborhood level but require the EPA correction enabled.
• After the event: document the dates, AQI readings, and respirator distribution. This is what an OSHA or state-level audit will ask for.

How Smog Report fits in

Smog Report is a free iOS app sourced from EPA AirNow. For site safety use:

• Site superintendent phone: Live Activities push lock-screen updates when AQI in the site's area crosses thresholds you set (e.g., AQI 100 advisory, 150 mask-available, 200 mandatory). No app launch required to see the current number.
• Safety manager phone: Siri voice queries ("Hey Siri, what is the air quality?") for hands-free morning toolbox checks.
• Documentation: the in-app history can be screenshotted for safety logs. (Smog Report doesn't pull arbitrary historical data — for an OSHA audit you'll want to also save daily PDFs from airnow.gov.)

No account required; nothing is sent to a server. The app is free and there's no enterprise tier or contract — for a site team, have each person install it from the App Store individually.

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