Carbon Monoxide Related Resources

What This Page Is, and What It Is Not

Most "CO links" pages on the internet are dumping grounds: long lists of every agency and trade group anyone has heard of, with no indication of why each one is worth your attention. This page is the opposite. Each entry below is here because it answers a specific question (where the law is, what the equipment must do, where the incident data lives, what an operator's duties are) and because the answer comes from a primary source rather than a summary of a summary. Links are reviewed periodically and updated when official guidance changes. When two resources cover the same ground, only the one closer to the primary source stays.

What this page does not do: replace medical advice, recommend treatments, or interpret your specific situation. For anything personal, see a clinician or qualified attorney. Everything below is general safety reference.

Start Here (SilentShadow Guides)

Federal Agencies (US)

The four agencies below carry the bulk of US CO authority. They publish, in this order, the consumer-facing overview, the consumer-product incident data, the indoor-air policy, and the occupational exposure framework. Read each for its specific role rather than as duplicates.

  • CDC, Carbon Monoxide overview. We include this as the layperson reference. CDC publishes the general definition, symptoms, and high-level prevention; it does not publish equipment specs or incident data.
  • US CPSC, Carbon Monoxide Information Center. The single most useful US source for incident data: annual non-fire CO death estimates by product category (generators, heaters, fireplaces), recall notices, and CO-related rules. The 2020 annual estimate (211 deaths from consumer products; 92 generators; 33 portable heaters) lives here.
  • US EPA, CO and indoor air quality. We list this because EPA owns the indoor-air pollutant framework. It is the regulatory authority behind some local code requirements; not the right resource for treatment or alarm-buying decisions.
  • ATSDR/CDC, Toxicological Profile for Carbon Monoxide. The full ATSDR profile is dense and academic. Worth scanning if you want the exposure-effect data behind general safety guidance. Probably not the first read for a homeowner with a beeping alarm.

Reference materials we link to but do not endorse beyond their scope:

Generator and Outage Safety

Outages and storms are a major risk period because portable generators can produce deadly CO. Use only outdoors and far from openings.

Related guide: Prevention checklist.

Workplace Exposure: OSHA and NIOSH

Carbon monoxide is a significant occupational hazard in industries involving combustion engines, welding, furnaces, and confined spaces. OSHA and NIOSH provide workplace exposure limits and guidance for employers and workers.

OSHA's permissible exposure limit (PEL) for carbon monoxide is 50 ppm as an 8-hour time-weighted average. NIOSH recommends a lower ceiling of 35 ppm (TWA) and 200 ppm as a ceiling limit. These limits apply to workplace settings, residential environments use different guidelines. For home safety, CO alarms are your primary protection.

Equipment Standards and Codes

Three documents govern the alarm in your hallway: UL 2034 for the alarm itself, NFPA 72 for where to install it, and ANSI Z21.11.2 for unvented gas heaters that share the airspace. Each entry has a specific reason it is on this list.

  • UL 2034, Single and Multiple Station Carbon Monoxide Alarms. The primary performance standard for residential alarms. The reason we cite the time-to-alarm thresholds (70 ppm between 60 and 240 minutes, 150 ppm between 10 and 50 minutes, 400 ppm between 4 and 15 minutes) across the site is because UL 2034 is what manufacturers must meet to put a UL mark on the unit.
  • NFPA 72, National Fire Alarm and Signaling Code. The placement and installation rules behind most state and local code requirements, with household CO alarms in Chapter 29 and commercial system detection in Chapter 17. This is where NFPA 720 went. Two dates get run together in most accounts of it and they are three years apart: 2015 is when the last edition of 720 was published, and 14 August 2018 is when the Standards Council approved the withdrawal and the move into NFPA 72, in the Annual 2018 revision cycle. The requirements have sat in NFPA 72 since its 2019 edition. Older statutes still cite 720 by number, so check the edition your jurisdiction adopted.
  • ANSI Z21.11.2-2016, Unvented Gas Room Heaters. We include this because the oxygen depletion sensor is the only equipment rule that shuts a heater off before the room becomes dangerous rather than warning someone afterwards: CPSC describes the ODS as sensing "when the oxygen level in a tent or camper drops below 18 percent", at which point "the ODS closes the gas valve and shuts off the heater". Its history is worth knowing, because the requirement is voluntary today and got there by an unusual route. CPSC proposed a mandatory standard in 1980, when unvented gas heaters were killing "about 70 a year", noting that "the ODS never has been used on American heaters" though "a similar device has been used successfully in Europe for many years". The mandatory standard took effect in December 1981. In May 1983 the Commission voted 3 to 2 to begin revoking it, on the finding that the ANSI and AGA voluntary standard "would be as effective as the mandatory standard", with over 95 per cent of that year's heaters already conforming. So the rule that protects you here is this ANSI standard, not a federal one, and ANSI sells it. The CO limit it sets, 200 ppm air-free for an unvented room heater against 400 ppm for a vented central furnace, can be read free in Table 1 of ANSI/BPI-1200-S, and the scope on the ANSI listing itself is readable without buying it: heaters up to 40,000 Btu/hr, with 10,000 the ceiling for one suitable for a bedroom and 6,000 for a bathroom.
  • NFPA, Carbon Monoxide Safety Resources. Operational educational materials at the consumer-facing layer. Useful as a starting point; the actual code language is in the standards above.

When buying a CO alarm, the UL 2034 mark on the box is the certification that matters. Without it, the unit has not been tested against the time-to-alarm thresholds above. For placement guidance derived from NFPA 72, see our detector placement guide.

Which of These Three You Can Open

Two of the three links above go to a shop rather than to a document, and it is worth knowing which before you click. The UL 2034 link is a product listing on UL's own store, and the ANSI Z21.11.2 link is a listing on the ANSI webstore. Neither shows you the standard. Anybody quoting UL 2034 thresholds on the open web, this site included, is working from a copy somebody bought.

NFPA 72 is the exception, and the difference matters if you want to read the placement rules behind your state's code rather than take our word for them. NFPA publishes its codes for public reading at no charge, and in its own words: "NFPA makes its codes and standards available online to the public for free. All you need is an NFPA account." The route is to open the list of codes and standards, find 72, pick the edition year your jurisdiction adopted, then use the View Free Access button and accept the terms. Two limits come with it. You will be asked to sign in or create an account first, and the viewer is read-only. NFPA states the reason plainly: "documents cannot be downloaded or printed, because we rely on the revenues from people who want to own their own copies to fund the mission."

For a reader checking one requirement, that is enough. Household CO alarms sit in Chapter 29, so the free viewer gets you to the actual clause your inspector is working from, on the edition your state adopted, without buying anything.

State Laws and Compliance

Counted from our own records rather than from the figures in circulation, and counted twice, because one number cannot carry this on its own. 49 of 51 US jurisdictions establish a statewide carbon monoxide requirement outright, reaching homes, rentals or lodging. Add the 2 whose reach was traced to a stated test rather than to a plain yes, Mississippi and Texas, and it is 51. Neither of those two is a jurisdiction where nothing applies: in one the fire code reaches a hotel above a stated height and in the other the answer turns on whether the property sits inside a city limit, and each state page sets out the test with its citation.

Scope varies by an order of magnitude underneath both numbers. Some requirements reach only new construction, some only rentals, some only lodging, and a few only named facility types such as schools or daycares, so a count tells you who has a rule and nothing about whether it reaches you. The per-jurisdiction breakdown is at our CO detector laws hub, and reading your own is the most useful thing you can do once the alarms are up.

Where Your Own Situation Is Answered

Whether a requirement reaches you turns on how you occupy the building rather than on the gas, so the rest of this site is organised that way. Each entry below answers a different occupancy question, and none of them repeats another.

Frequently Asked Questions

How do you choose which resources to list?

An entry has to be the document that creates the rule, or the agency that publishes the number, rather than a page describing either. That is why the standards here link to UL, ANSI and NFPA instead of to articles about them, and why no opinion blog appears. Where we could not verify a link the way we verify the rest, we say so in the entry.

Can you give me a phone number to call?

Emergency numbers vary by country and region. If you suspect exposure, call your local emergency number or contact your local fire department.

Check Your State's CO Detector Requirements

Requirements vary by state. See rules for popular states:

See all 50 states + DC →

Last updated: August 12, 2026