Indoor air quality standards in the United States are not one rule but three overlapping systems: OSHA enforces legal exposure limits for roughly 500 air contaminants in workplaces, the EPA publishes mostly advisory guidance for homes and schools (with binding rules only in narrow areas like lead paint disclosure), and ASHRAE writes the ventilation benchmarks that many local building codes adopt as law. Which system applies to you depends entirely on where you are standing. The air in your office has hard legal limits your employer must meet. The air in your home is largely your responsibility.
What OSHA Requires in the Workplace
Every employer covered by the Occupational Safety and Health Act owes workers a workplace free from recognized hazards likely to cause death or serious physical harm. That duty comes from Section 5(a)(1), the General Duty Clause, and it acts as a catch-all when no specific standard applies.1Occupational Safety and Health Administration. Occupational Safety and Health Act – Section 5, Duties
For air contaminants the controlling regulation is 29 CFR 1910.1000, which lists permissible exposure limits (PELs) across three tables. These apply whether you work in a factory or a standard office.2eCFR. 29 CFR 1910.1000 – Air Contaminants Most PELs are eight-hour time-weighted averages: cumulative exposure across a full shift cannot exceed the listed concentration. Substances marked with a “C” carry ceiling values that cannot be exceeded at any point in the workday, even briefly. Employers must use engineering or administrative controls first, turning to personal protective equipment only when those controls cannot bring exposure within limits.3eCFR. 29 CFR 1910.1000 – Air Contaminants
Penalties for Noncompliance
OSHA enforces through inspections. For 2025 (unchanged for 2026 after the federal government canceled inflation adjustments for that year), the maximum fine for a serious violation is $16,550, and willful or repeated violations can reach $165,514 per violation.4Occupational Safety and Health Administration. Federal Civil Penalties Inflation Adjustment Act Annual Adjustments Criminal exposure also exists. An employer whose willful violation causes an employee’s death faces up to six months in prison and a $10,000 fine on a first conviction, rising to one year and $20,000 for a subsequent offense.5Office of the Law Revision Counsel. 29 USC 666 – Civil and Criminal Penalties
Exposure Records
Employers must keep records of employee exposure to hazardous contaminants for at least 30 years under 29 CFR 1910.1020. That means workers and former workers can request their exposure history long after leaving a job, which matters if health problems surface years later.6Occupational Safety and Health Administration. 29 CFR 1910.1020 – Access to Employee Exposure and Medical Records
EPA Guidance for Homes and Schools
The EPA’s role in residential indoor air is advisory, not regulatory. The agency does not inspect homes, fine homeowners, or set enforceable concentration limits for most household pollutants. Its Indoor Air Quality program publishes guidance built around source control and proper ventilation.7United States Environmental Protection Agency. Introduction to Indoor Air Quality For schools, the EPA offers the IAQ Tools for Schools program to help administrators build management plans targeting common problems like poor ventilation and excess moisture.
The agency does carry regulatory weight in two specific hazard areas: radon (in limited real estate contexts) and lead-based paint.
Radon
The EPA’s action level is 4.0 picocuries per liter (pCi/L), above which it recommends installing a mitigation system. It also recommends homeowners consider fixing levels between 2 and 4 pCi/L, since no known level of radon exposure is truly safe.8U.S. Environmental Protection Agency. What is EPAs Action Level for Radon and What Does it Mean Mitigation for a single-family home generally costs between $900 and $2,800, depending on foundation type, home age, and regional labor rates.
No general federal law requires radon disclosure in a residential sale. Federal involvement is limited to certain HUD-related transactions, where mortgagees under FHA-insured loans must provide buyers with information about radon testing.9U.S. Environmental Protection Agency. Radon and Real Estate Resources Many states impose their own disclosure requirements, so buyers should check local rules rather than assume federal law covers them.
Mold
There are no federal numerical limits for indoor mold. The EPA has explicitly stated that because no federal mold standard exists, sampling alone cannot determine whether a building is compliant with any regulation.10U.S. Environmental Protection Agency. A Brief Guide to Mold, Moisture and Your Home Guidance centers on a practical principle: control moisture and you control mold. Water-damaged areas should be dried within 24 to 48 hours. Patches smaller than about 10 square feet can typically be handled without professional help, while larger areas or contamination in HVAC systems warrant a contractor with remediation experience.
Lead-Based Paint Disclosure
For housing built before 1978, federal law requires sellers and landlords to disclose any known lead-based paint hazards before a sale or lease closes. The seller must provide an EPA-approved lead hazard pamphlet, share any available testing records, and give the buyer a 10-day window to arrange an inspection, which the buyer can waive in writing.11eCFR. 24 CFR Part 35 Subpart A – Disclosure of Known Lead-Based Paint and Lead-Based Paint Hazards Upon Sale or Lease of Residential Property Violations carry civil penalties of up to $10,000 per occurrence, and a knowing violator can be held liable for triple the buyer’s or renter’s actual damages plus attorney fees.12eCFR. 24 CFR Part 35 – Lead-Based Paint Poisoning Prevention in Certain Residential Structures Sellers and their agents must keep signed disclosure records for at least three years.
ASHRAE Ventilation Standards
Engineering benchmarks for how much fresh air a building needs come from the American Society of Heating, Refrigerating and Air-Conditioning Engineers. ASHRAE Standard 62.1 covers commercial buildings; Standard 62.2 covers residential dwelling units. Both define minimum ventilation rates intended to maintain acceptable indoor air quality.13ASHRAE. Standards 62.1 and 62.2
These are consensus standards, not federal regulations on their own. They become legally enforceable when local jurisdictions adopt them into building codes, which many do for new construction and major renovations. Mechanical designers use them to calculate the required volume of outdoor air based on occupancy and floor area, then size fans and duct systems accordingly. Buildings that fail to meet code-adopted requirements can be denied a certificate of occupancy or face mandatory retrofits.
Common Pollutant Limits at a Glance
Different agencies set limits for different pollutants, and the numbers depend on whether you are looking at a workplace rule or a residential guideline.
Carbon Monoxide
The EPA’s national ambient air quality standard caps carbon monoxide at 9 parts per million (ppm) averaged over eight hours, a level not to be exceeded more than once per year.14Agency for Toxic Substances and Disease Registry. Carbon Monoxide – Public Health Statement OSHA’s workplace PEL is 50 ppm as an eight-hour TWA. The gap reflects the difference between a public health standard protecting children and people with heart disease and a workplace standard set for healthy adults.
Asbestos
OSHA’s PEL for asbestos is 0.1 fiber per cubic centimeter of air as an eight-hour TWA, applying to both general industry under 29 CFR 1910.1001 and construction work under 29 CFR 1926.1101.15Occupational Safety and Health Administration. 29 CFR 1910.1001 – Asbestos There is no safe level of asbestos exposure; the PEL is the lowest concentration OSHA determined was feasible for employers to achieve, not a health-based safe threshold.
Lead
The workplace PEL for airborne lead is 50 micrograms per cubic meter as an eight-hour TWA. For shifts longer than eight hours, the limit drops proportionally using a formula that divides 400 by the number of hours worked.16eCFR. 29 CFR 1910.1025 – Lead In residential settings, lead exposure is managed through paint disclosure rules and drinking water standards rather than air concentration limits.
Formaldehyde
Formaldehyde has both a long-term and a short-term OSHA limit. The eight-hour TWA PEL is 0.75 ppm.17Occupational Safety and Health Administration. 29 CFR 1910.1048 – Formaldehyde The short-term exposure limit is 2 ppm over any 15-minute period, preventing acute irritation from brief high-concentration bursts.18eCFR. 29 CFR 1910.1048 – Formaldehyde Formaldehyde is common indoors because it off-gases from pressed-wood products, certain insulation materials, and some adhesives.
Carbon Dioxide
Carbon dioxide is not toxic at typical indoor concentrations, but it serves as a proxy for whether a space has enough fresh air. OSHA’s workplace PEL is 5,000 ppm as an eight-hour TWA, a level rarely approached in office settings.19Centers for Disease Control and Prevention. Carbon Dioxide – NIOSH Pocket Guide to Chemical Hazards The commonly cited 1,000 ppm indoor benchmark has a more complicated history. ASHRAE’s current position is that Standard 62.1 does not set a CO2 limit, and the 1,000 ppm figure from an older edition was removed because people kept misinterpreting it as an air quality limit rather than a rough indicator of ventilation rate per person.20ASHRAE. ASHRAE Position Document on Indoor Carbon Dioxide Building managers still use CO2 readings to adjust ventilation in real time, but the readings measure stuffiness, not danger.
Fine Particulate Matter (PM2.5)
The EPA’s outdoor national ambient air quality standard for PM2.5 was tightened in 2024 to 9.0 micrograms per cubic meter as an annual average.21U.S. Environmental Protection Agency. National Ambient Air Quality Standards (NAAQS) for PM No separate federal standard exists for indoor PM2.5, but indoor levels are heavily influenced by outdoor air, cooking, candles, and tobacco smoke. Many consumer air quality monitors track PM2.5, making it one of the easier pollutants for individuals to watch on their own.
Reading the Measurement Types
Most of the limits above use one of a few measurement types. A time-weighted average (TWA) represents the average concentration a person is exposed to over a standard eight-hour workday; brief spikes are allowed if the shift average stays within the limit.2eCFR. 29 CFR 1910.1000 – Air Contaminants A short-term exposure limit (STEL) captures a 15-minute window and exists to prevent acute reactions from high-concentration bursts even when the eight-hour average would be fine. Ceiling values are the strictest category: the concentration cannot be exceeded at any point, period.
Residential measurements work differently. Radon test kits collect data over days or months to produce a long-term average. Mold is assessed visually and through sampling rather than against numerical thresholds, since no federal standard exists for acceptable spore counts.
What Landlords Actually Owe Tenants
Residential landlords occupy a regulatory gray area. No broad federal statute requires them to test for or remediate most indoor pollutants. The federal obligations that do exist are hazard-specific: the lead-based paint disclosure rules apply to pre-1978 housing, and federally assisted housing under HUD programs must meet site and neighborhood standards that prohibit serious adverse environmental conditions, including abnormal air pollution.22eCFR. 24 CFR 982.614 – Group Home Housing Quality Standards
Beyond those specific rules, landlord air quality duties come from state and local habitability standards. Many states require landlords to maintain habitable premises, and courts have sometimes treated severe mold, persistent carbon monoxide issues, or failed ventilation systems as habitability violations. Federal law protects renters mainly from lead and radon in limited contexts. State landlord-tenant law is where most indoor air quality disputes actually get resolved.
Testing Your Air
In workplaces, air quality testing is typically performed by industrial hygienists who use calibrated monitors and pump-driven sampling devices that pull measured volumes of air through collection media. Samples go to accredited laboratories for analysis.
For homeowners, the most common entry point is a radon test kit: a passive collector placed in the lowest livable area of the home for several days (short-term) or several months (long-term), then mailed to a lab. Mold testing kits are widely available, though the EPA cautions that since no federal mold standard exists, test results alone cannot tell you whether your home passes or fails.10U.S. Environmental Protection Agency. A Brief Guide to Mold, Moisture and Your Home Visible mold growth with a known moisture source is often more actionable than a lab number. Professional residential air quality assessments typically run a few hundred to over a thousand dollars depending on scope and sample count.
Consumer-grade monitors have improved and can now track PM2.5, carbon dioxide, VOCs, temperature, and humidity in real time. They are useful for spotting ventilation problems or identifying pollution sources like a malfunctioning gas appliance. They lack the precision of professional instruments and should not be treated as substitutes for formal testing when a specific hazard is suspected.