Three Deaths in a Tank at Hosur: What Must Happen Before Anyone Steps Into a Tank

On the evening of Monday, 9 November, three contract workers died while doing maintenance on a water tank at the Tata Electronics plant in Hosur, Krishnagiri district, Tamil Nadu, where parts for Apple iPhones are made. Reuters reported that they died of asphyxiation.

According to India TV, the three had entered an effluent treatment plant (ETP) tank to remove sludge and silt. They were Kaveri, 30, from Hosur, and B Akmal and M Sarathi Kumar, both 28, from Dharmapuri district, and they were engaged through a contractor rather than employed by Tata Electronics. They were declared brought dead at a private hospital in Hosur. The Krishnagiri District Collector said they died of suffocation while removing sludge and that a full investigation has been ordered. Tamil Nadu's Industries Minister said the incident "will be thoroughly investigated" and that "the safety and dignity of every worker must remain paramount." Tata Electronics had not commented when those reports were published.

The investigation will establish exactly what went wrong in this case, and we will not guess at it. But deaths like these are not rare in India, and they happen in the kind of structures we design and build every week: underground water sumps, sewage treatment plants (STPs), septic tanks, rainwater recharge pits and wells. This post explains why these spaces are so dangerous and what has to be in place before anyone goes in.

Why a tank can kill in minutes

A tank, sump or chamber with a small opening and no steady airflow is a confined space. Three things go wrong inside one:

• Too little oxygen. Sludge, silt and organic matter use up oxygen as they decay. Rust on steel does the same. Normal air has about 21% oxygen; below about 19.5% it is unsafe, and at very low levels a person can collapse after a few breaths, with no warning.
• Toxic gas. Disturbing sludge releases gases that were trapped in it, above all hydrogen sulphide (the rotten egg smell). At high levels it deadens the sense of smell, so the warning disappears just as the danger rises. Methane and carbon dioxide also build up and push out the oxygen.
• The rescue that adds to the toll. When one worker collapses, the person nearest usually climbs in to help, without breathing apparatus, and collapses too. In many confined space accidents in India, more than one life is lost this way.

None of this depends on whether the tank holds sewage, industrial effluent or "clean" water. A drained drinking water sump with a layer of silt at the bottom can be as dangerous as an STP tank.

What the law already requires

The Factories Act, 1948 (Section 36) says no one may enter a chamber, tank, pit or other confined space where dangerous fumes may be present unless it has been made safe, a competent person has certified it in writing after testing, and the worker wears a suitable breathing apparatus and a belt secured to a rope held by someone outside. For sewers and septic tanks, the Prohibition of Employment as Manual Scavengers and their Rehabilitation Act, 2013 bans hazardous cleaning by hand without protective gear and safety devices. The rules exist. The failures happen on the ground, usually when the work is handed to a contractor and treated as a routine cleaning job.

The checklist before anyone enters

Whether it is a factory ETP, a society's STP, an underground water tank or a recharge well, we follow the same steps on our sites, and every owner can ask their contractor for them:

1. A written permit to work, signed by a supervisor, naming who goes in, for how long, and who stands outside.
2. Drain, isolate and lock out. Stop inflow, close and tag valves, and switch off and lock pumps, blowers and agitators.
3. Ventilate. Open every manhole and run a blower to push fresh air in for at least 30 minutes before entry, and keep it running throughout.
4. Test the air at the top, middle and bottom with a calibrated multi-gas detector: oxygen, hydrogen sulphide, carbon monoxide and flammable gas. No entry unless oxygen is between 19.5% and 23.5% and the toxic gases are below their limits. Keep a personal gas monitor on the worker inside.
5. Harness, lifeline and tripod. The person inside wears a full-body harness tied to a winch or tripod, so they can be pulled out without anyone else going in.
6. An attendant who never enters, watching and talking to the worker the whole time, with a phone to call for help.
7. Rescue gear at the opening: breathing apparatus, a first aid kit and the nearest hospital's number. If it is not there, nobody goes in.
8. Trained people only. Contract workers need the same training and equipment as permanent staff.

Better still: design tanks so nobody has to go in

Most tank entries are for removing sludge and silt. Good design removes most of that need:

• Sloped or hoppered floors with sludge draw-off pipes, so sludge can be pumped out from above.
• Desludging by suction tanker or a submersible pump, not by buckets and shovels.
• Silt traps and screens at the inlet, so less settles inside the tank in the first place.
• Large, well-placed manholes and permanent vent pipes, so air moves and a person can be lifted out quickly.
• Fixed, corrosion-free ladders and space at the top for a tripod.

We build these features into the sewage treatment plants we design for housing societies, schools and offices. If your plant is overloaded and silting up faster than it should, check its size with the STP capacity calculator. The same rule applies to rainwater structures: a recharge pit or a borewell recharge system should have a filter chamber that can be cleaned from the surface, and a pond being desilted during pond rejuvenation should be dug out by machine, not by people standing in deep sludge.

Why this matters more as industry treats more water

Factories in water-stressed areas are rightly being pushed to treat and reuse their wastewater. Krishnagiri district, where Hosur is, already pumps about 92% of the groundwater it recharges each year (see the district page), and Tamil Nadu's cities have their own rainwater harvesting mandate. More treatment and reuse means more tanks, sumps and sludge, and more cleaning jobs. Water conservation cannot come at the cost of the people who keep these systems running.

For facility managers, RWAs and CSR teams

If you run a factory, a society or a campus, ask three questions this week: who cleans our tanks, what gas detector do they carry, and who is standing outside when they go in? If the answers are vague, stop the next cleaning until they are not. For an audit of an existing STP, ETP or water tank, or to design one that rarely needs entry, send us the details. Companies funding water projects through CSR water conservation can make safe operation and maintenance a condition of every structure they pay for.

Sources

• Deaths, location and the minister's statement: Reuters via Free Malaysia Today, 10 November 2026.
• ETP tank, names of the workers, the collector's statement: India TV News, 10 November 2026.
• The original report: The Times of India, "Three workers killed during water tank maintenance at Tata iPhone parts factory in Tamil Nadu", 10 November 2026.
• Groundwater figures: CGWB Dynamic Ground Water Resources assessment, 2025, as shown on our district pages.