Most homes and offices don't. A sewer smell there is a plumbing leak to fix, not a gas to monitor. A hydrogen sulfide meter earns its place where gas collects: sewage ejector rooms, lift station wet wells, manholes and pits. OSHA says the air in those spaces must be tested by a qualified person before anyone goes in.
Why a detector is the wrong fix for a smelly bathroom
Plumbing is designed so sewer gas never reaches the room. Every fixture has a trap that holds a water seal, and the vent system carries gas out through the roof. Wisconsin's health department lists the usual ways sewer gas gets indoors: a floor drain, a leaking or blocked roof vent, or cracks in the foundation when gas is in the soil. Each of those is a repair.
A detector in that room would tell you what your nose already told you. It won't stop the gas. Refill the traps, check the vent and have a plumber find the leak if it keeps coming back. Start with why a bathroom drain smells like sewer, or for a whole building, sewer gas smell in a commercial building. If the smell is in your tap water rather than the air, read whether a rotten egg smell in tap water is harmful instead.
Where a hydrogen sulfide meter does make sense
OSHA's fact sheet says hydrogen sulfide is heavier than air and collects in low, enclosed, poorly ventilated spots such as basements, manholes and sewer lines. That is the list to think about.
| Place | Detector worth it? | Why |
|---|---|---|
| Bedroom, office, restroom | Rarely | Fix the trap, vent or seal. Leave and call 911 if the smell is strong. |
| Sewage ejector or sump room | Often | Sewage sits in a pit, and a failed cover gasket or vent lets gas into a small room. |
| Lift station wet well or valve vault | Yes, before entry | A confined space that can hold high levels. |
| Manhole, grease interceptor vault, septic tank | Yes, before entry | OSHA requires air testing first. Never enter without training and equipment. |
| Restaurant or plant with wastewater pretreatment | Often | Staff work near sources every day. |
What OSHA and the plumbing code require
### Before anyone enters a pit or vault
OSHA's fact sheet lays out the order. Before entering an area where hydrogen sulfide may be present, a qualified person must test the air for it with monitoring equipment such as detector tubes or a multi-gas meter, and check whether fire or explosion precautions are needed. If the gas is there, the space gets continuous ventilation. If ventilation can't remove it, the person going in needs respiratory protection and rescue gear. OSHA's confined space rules add their own requirements on top.
Arizona runs its own OSHA program through ADOSH, which enforces the federal general industry and construction standards. So a property manager sending a maintenance tech into an ejector pit is in the same place as any employer: test first.
The part people skip is the rescue rule. OSHA says never attempt a rescue in an area that may contain hydrogen sulfide without respiratory protection and training. If someone collapses in a pit, call 911. Going in after them is how one victim becomes two.
### What plumbing code relies on instead
The plumbing code handles sewage pits with construction, not alarms. The 2024 International Plumbing Code, the model behind most Valley cities' plumbing rules, says a sump that takes building drainage must be "tightly covered and vented" (Section 712.1), and the pit must have "a gastight removable cover" (Section 712.3.2). The Uniform Plumbing Code, which Phoenix also allows, calls for a bolt-and-gasket manhole cover and a vent on sumps too (Section 710.10). Neither section calls for a gas alarm. If a pit room smells, the cover gasket or the vent is the first suspect. Our page on why an ejector or lift station pit smells covers those failures.
Three Valley examples
The right answer changes with the building and with who goes near the sewage.
These are made-up examples to show the decision, not real events.
A house with a smelly guest bath. Nobody has used the shower in a month and the hallway smells like rotten eggs. No detector needed. Run water into every drain in that bathroom, and if the smell comes back, have the trap, toilet seal and vent checked.
An office building with a sewage ejector in the parking level. Restrooms on the lower level drain into a pit, and the pump room smells on hot afternoons. A portable H2S meter for the maintenance lead makes sense, and so does fixing the cover gasket and vent. Nobody should lift the pit lid or climb in without the air being tested first.
A restaurant with a grease interceptor vault out back. The kitchen staff never enter it, but the pumping contractor does. The contractor's crew should be testing the air before entry under OSHA's rules. The restaurant's own job is keeping the interceptor on schedule so it doesn't turn septic.
If you do get a detector
A detector is a backup for a space that can collect gas, not a fix for a leak. If your building has one of those spaces, here's how to set it up so it actually protects people.
### What levels an alarm should be set to
If you do mount an H2S alarm, set it with the published limits in mind. NIOSH recommends a 10 ppm ceiling for any 10-minute period. OSHA's general industry ceiling is 20 ppm, and NIOSH treats 100 ppm as immediately dangerous to life or health. OSHA's control guidance also says employers must provide respiratory protection when engineering and work-practice controls can't keep levels below OSHA's limit. An alarm that only sounds at 100 ppm is set to warn you after the danger arrives. Follow the manufacturer's setup instructions, and base the alarm points on the lower recommended numbers, not the highest one.
### Keep your carbon monoxide alarms anyway
A hydrogen sulfide meter and a CO alarm do different jobs. The Consumer Product Safety Commission recommends CO alarms on every level of a home and outside sleeping areas, and that advice has nothing to do with sewer gas. Don't swap one for the other. If a single plug-in unit claims to cover both, check its listing and manual for exactly which gases it senses, and keep a separate, dedicated CO alarm where CPSC recommends one.
### Buy the right kind
- Get a meter that reads H2S in ppm. A combustible gas sniffer reads methane and won't tell you much about the rotten-egg gas. See do sewer gas detectors work for the difference.
- Keep it tested. OSHA's bulletin on gas monitors passes along the industry advice to bump test or calibration check before each day's use. A meter that has never been checked is not a safety device.
- Don't let it replace your judgment. OSHA warns that the sense of smell fades fast around hydrogen sulfide, so a meter is a better guide than your nose. If the meter alarms or anyone feels sick, leave first.
For the actual numbers a meter compares against, see OSHA's limits for hydrogen sulfide.
HQ Plumbing offers 24/7 emergency service for commercial buildings and homes. We fix the cover, vent, trap or line that lets sewer gas out, so you're not stuck monitoring it.