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"The Deadly Drain": Probable Hydrogen Sulfide Poisoning in a Bathroom Stall in Unaizah.


Hydrogen sulfide (H2S) can be generated from a number of natural and manmade sources and is well known for causing rapid knockdown, unconsciousness and death in humans at concentrations over 700 ppm. We investigated an incident of probable H2S poisoning involving 2 deaths in a bathroom stall in a compound housing 41 furniture workers in Saudi Arabia.


We interviewed all surviving workers and involved medical staff at the hospital to establish the time sequence and description of the fatal incidents. We measured, mapped and inspected the bathrooms, drains and sewage system of the compound. We generated smoke in the sewage line to retrace the pathway which gasses generated in the sewage would follow.


Thirty minutes after pouring 98% H2SO4 into the drains of 7 of 8 bathroom stalls, a worker returned to bathe in the only untreated stall (Stall #8). He was found after 45 minutes lying immobile on the floor of the stall. The first rescuer also collapsed inside the stall. Two other rescuers collapsed immediately outside the stall. At the hospital 20 minutes later, the first two workers were pronounced dead. The other two recovered completely within 24 hours using only oxygen. No physical or physiologic abnormalities were detected on the two surviving workers. All surviving rescuers reported smelling rotten eggs. All 8 stalls were 2 m3 with a tight fitting door rising from 0.5 cm above the floor to 0.5 m from the ceiling. Drains from the 8 stalls joined into a common drain line, then to a 16 m3 holding tank 3 m down line. This system had no vertical venting pipe. Smoke generated in the line near the tank appeared in stall 8 after less than 1 minute and rapidly rose to 1 m high inside the stall. No smoke appeared in any other stall or from the lid on the sewage tank.


Rapid knockdown and death, the smell of rotten eggs, and the venting of gasses from the sewer drain into the deadly stall 8 all suggest that H2S poisoning was responsible for this incident. Using 98% H2SO4 to clean drains and sewage lines is a common practice in Saudi Arabia, and many sewage disposal systems probably have similar designs. We recommend that warnings about using acid drain cleaners in closed sewage systems be circulated to municipal authorities, employers of laborers, and to the general public. Intervention: The drains on all stalls were replaced and the system was equipped with a vertical ventilation pipe.