Hydrogen sulphide is an inorganic gas produced when bacteria reduce sulphate in the absence of oxygen. It is not emitted by building materials, and it is not an organic compound, so it sits outside the scope of a conventional volatile organic compound survey entirely. Wherever organic matter decomposes anaerobically — in a drainage system, a grease trap, a pump chamber or a stagnant water main — the conditions that generate it are present.
Hydrogen sulphide is an inorganic gas produced when bacteria reduce sulphate in the absence of oxygen. It is not emitted by building materials, and it is not an organic compound, so it sits outside the scope of a conventional volatile organic compound survey entirely. Wherever organic matter decomposes anaerobically — in a drainage system, a grease trap, a pump chamber or a stagnant water main — the conditions that generate it are present.
Two physical properties shape how it is encountered. It is denser than air, so it collects in low points — sumps, pits, basements and tank chambers — rather than dispersing evenly through a room. And its odour, the familiar rotten-egg smell, is detectable at very low concentrations, which makes it one of the few contaminants that occupants reliably report before any instrument is brought to the building.
The dominant pathway in UAE buildings is sewer gas entering through a dry trap. Every floor gully, shower drain, basin and kitchen waste relies on a small volume of water held in a U-bend to separate the room from the drainage system, and that seal is maintained only by use. Where a bathroom or kitchen goes unused for weeks — a vacant apartment, a hotel room out of service, a plant room floor gully that nothing ever discharges into — the water evaporates and the barrier is gone. In a hot, dry, mechanically conditioned interior that happens fast.
UAE building stock makes this common rather than exceptional. High-turnover residential and hotel portfolios carry a standing proportion of unoccupied units, seasonal occupancy leaves whole floors empty through the summer, and handover-to-occupation gaps in new towers can run for months with the drainage installed and untouched. Unsealed floor gullies, and gullies fitted without a functioning trap at all, add a permanent opening where the seal was never there to lose.
Beyond the trap itself, an inadequately vented drainage stack draws seals out by siphonage when a discharge passes, producing an intermittent odour that appears only when a flat above is used. Grease traps, pump chambers and holding tanks generate the gas directly. Tanker discharge points and the wider sewerage network are a further source at the site boundary. Stagnant water systems complete the list: unused risers, dead legs and tanks left standing through a long void period go anaerobic in the same way.
Temperature accelerates the biology. Warm sewage and warm standing water sustain sulphate-reducing bacteria far more effectively than cool systems do, so a given drainage installation generates more gas here than the same installation would in a temperate climate. The conditioned interior works against the building at the same time: dry supply air evaporates trap seals quickly, and extract systems in bathrooms and kitchens hold those rooms at negative pressure, which is exactly the pressure regime that draws gas up through a trap that has lost its water.
At the concentrations associated with a drainage odour complaint, hydrogen sulphide is an irritant. Reported effects are irritation of the eyes and the upper respiratory tract, sore throat, cough, headache and nausea, and the odour itself is a substantial part of the complaint — an intermittent smell of sewage in a home or workplace is distressing independently of any toxic effect. Occupants with persistent symptoms should be directed to occupational health or a medical practitioner.
One property matters more than any other, and it is the reason this gas is treated as a safety hazard rather than a comfort one. Hydrogen sulphide paralyses the sense of smell. At low concentrations the odour is obvious; as concentration rises the olfactory response is deadened, and above a certain point the smell is lost altogether. The gas therefore becomes undetectable by nose precisely as it becomes dangerous, and the disappearance of an odour must never be read as the hazard having passed. Fatal exposures in sewers and tanks have followed that reversal.
A non-health effect is often what brings the problem to attention first. Hydrogen sulphide tarnishes silver and blackens copper, so silverware, jewellery, exposed copper pipework and the copper traces and contacts inside electronic equipment discolour and corrode. Repeated equipment failures in a server room, or a run of tarnished cutlery in a kitchen, have both led to the drainage system being investigated.
Like ammonia, hydrogen sulphide falls outside the standard organic methods. A sorbent tube analysed by thermal desorption under EPA Compendium Method TO-17 is not the right medium for it, a canister method will not report it, and a photoionisation detector gives no dependable result — such a detector reports a total response weighted by response factor and identifies no compound. Dedicated detection is required: an electrochemical sensor for real-time work, or a specific sorbent or impregnated medium analysed in a laboratory where a time-weighted result is needed.
Air measurement is rarely the whole investigation, because the useful evidence is usually structural. Inspection of trap seals, smoke or tracer testing of the drainage system, examination of stack venting, and checking of gully seals and service penetrations locate the entry route, and an intermittent source needs monitoring that runs long enough to catch the discharge events that produce it.
No UAE instrument sets a numeric indoor-air limit for hydrogen sulphide. It does not appear in Table 1, Table 2 or Table 4 of Dubai Municipality's Technical Guidelines for Indoor Air Quality for Healthy Life (DM-HSD-GU119-IAQ, Version 4, 11 December 2024), and it is not among the nine pollutants covered by the WHO Guidelines for Indoor Air Quality: Selected Pollutants. Being an inorganic gas, it is not captured indirectly either: it does not contribute to the total volatile organic compound figure, and the methods behind that figure do not retain it. In Abu Dhabi, the only instrument that ever carried numeric chemical exposure limits, the Occupational Standards and Guideline Values document of the Abu Dhabi Public Health Centre, is recorded by ADPHC as suspended.
A separate point should be made clearly. Entry into sewers, sumps, pump chambers, tanks and other confined spaces where this gas accumulates is not an indoor air quality activity, and nothing on this page applies to it. That work sits within occupational safety, and in the Emirate of Abu Dhabi it is governed by Code of Practice 27.0 on confined spaces within the ADOSH-SF framework of the Abu Dhabi Public Health Centre, with its own entry controls, gas testing regime, permit system and rescue arrangements.
Source control means closing the entry route, and for this gas that is almost always a plumbing intervention rather than a ventilation one. Trap seals should be restored and kept charged, by scheduled flushing of unoccupied units, or by fitting trap primers or waterless trap-seal devices where a fitting will never be used. Floor gullies and service penetrations should be sealed, stack venting checked where seals are being siphoned, and grease traps and pump chambers brought onto a maintenance schedule. Increased outdoor air masks an odour without removing its cause, and in UAE summer conditions carries a cooling-load penalty that makes it unsustainable as a permanent control. Re-testing should follow under comparable occupancy and drainage-use conditions.
No UAE instrument sets a numeric indoor-air limit for hydrogen sulphide. It does not appear in Table 1, Table 2 or Table 4 of Dubai Municipality's Technical Guidelines for Indoor Air Quality for Healthy Life (DM-HSD-GU119-IAQ, Version 4, 11 December 2024), and it is not among the nine pollutants covered by the WHO Guidelines for Indoor Air Quality: Selected Pollutants. Being an inorganic gas, it is not captured indirectly either: it does not contribute to the total volatile organic compound figure, and the methods behind that figure do not retain it. In Abu Dhabi, the only instrument that ever carried numeric chemical exposure limits, the Occupational Standards and Guideline Values document of the Abu Dhabi Public Health Centre, is recorded by ADPHC as suspended. A separate point should be made clearly. Entry into sewers, sumps, pump chambers, tanks and other confined spaces where this gas accumulates is not an indoor air quality activity, and nothing on this page applies to it. That work sits within occupational safety, and in the Emirate of Abu Dhabi it is governed by Code of Practice 27.0 on confined spaces within the ADOSH-SF framework of the Abu Dhabi Public Health Centre, with its own entry controls, gas testing regime, permit system and rescue arrangements.
No UAE instrument sets a numeric indoor-air value for hydrogen sulphide over any averaging period. It does not appear in Table 1, Table 2 or Table 4 of Dubai Municipality DM-HSD-GU119-IAQ Version 4 (11 December 2024), it is not among the nine pollutants covered by the WHO Guidelines for Indoor Air Quality: Selected Pollutants, and being an inorganic gas it is not captured within the Dubai Municipality total volatile organic compound figure either. In Abu Dhabi, the Occupational Standards and Guideline Values document of the Abu Dhabi Public Health Centre, the only instrument that ever carried numeric chemical exposure limits, is recorded by ADPHC as suspended.
Because the entry route is usually intermittent. A trap that has been siphoned by a discharge from a flat above admits gas only when that discharge occurs, and a dry gully in an unused bathroom admits it continuously until the seal is refilled. Monitoring has to run long enough to catch the events.
No. Hydrogen sulphide deadens the sense of smell as its concentration rises, so the odour weakens and then disappears at concentrations that are more hazardous, not less. The loss of a smell must never be treated as evidence that the gas has gone.
No. Sorbent tubes with thermal desorption, canister methods and photoionisation detectors are all built around organic vapours and do not give a reliable result for it. An electrochemical sensor or a dedicated sorbent method is needed instead.