It is certainly not a silent enemy. The hydrogen sulfide that killed the Casteldaccia workers knows how to get noticed. Its rotten egg smell is unmistakable (and unbearable). The environments in which it typically forms – sewers or hydrocarbon wells – make it an Erebus gas.
“Anaerobic degradation”
“Hydrogen sulfide is formed from the degradation of organic matter. This degradation occurs by bacteria in an anaerobic environment, i.e. in the absence of oxygen”, explains Luigi Petta, engineer, head of the water management laboratory of Enea, the national agency for new technologies, energy and sustainable development.
“It is a very powerful poison” confirms Carlo Locatelli, toxicologist, director of the Maugeri Poison Control Center in Pavia. “From the lungs it enters the bloodstream and kills all the cells into which it spreads. The most affected are those with a higher metabolism , therefore heart and brain”.
The remedies, once inhaled, are few. “It is as toxic as cyanide, but unlike cyanide it has no antidote. When accidents happen, we can try to treat the symptoms and try to resuscitate the victims.”
Hydrogen, but also methane and carbon monoxide
There is no shortage of degrading organic substance in sewer pipes. There are small amounts of oxygen, but certainly not too much air circulating there.
“Anaerobic reactions are triggered at the bottom of the sewer pipes, in the absence of oxygen” explains Petta. “In addition to hydrogen sulphide, methane and carbon monoxide are formed, other gases harmful to health”.
Casteldaccia, five workers died from fumes in the sewer system. Two of them had rushed to save their colleagues
by Alessia Candito and Francesco Patané
High (and deadly) concentrations
At high concentrations, the gas that smells like rotten eggs (also called hydrogen sulfide) can kill within 5 minutes. The first symptoms are cough, headache and dizziness. However, they often arrive too late for anyone to escape.
“It is well known that sewers are dangerous places,” confirms the Enea engineer. “I remember hearing this from my professors in college. This is why you can only go down there with lots of protection.”
Those who work in sewer systems or with hydrocarbons and risk encountering this gas often wear a helmet capable of detecting even minimal traces of it. “In the event of an alarm, it starts to ring unbearably” explains Locatelli. “In that case there is only one thing to do: put on the oxygen mask and escape.”
The putrid waste
In addition to the sewerage school case, there are more subtle situations. One of them may have misled the workers who died in Casteldaccia, in the Palermo area. In rivers rich in putrid algae, hydrogen sulfide can cause sudden fish deaths. For human beings, the danger can come from the tanks where putrid waste is left to settle for long periods.
“Sometimes a crust forms on the surface of these tanks,” explains Petta. “Grass can grow there, you don’t have the impression of being in danger. But if the crust is broken by stepping on it with your foot, the pockets of gas that have accumulated over time in the tank can escape, intoxicating those nearby. Or you risk falling in.”
The precedent in Pavia
In Villanterio, in the province of Pavia, another worker died in a tank of animal sewage in 2021. Everything seemed calm, he was freeing a pump that had become blocked with the water pipe. A whiff of hydrogen sulphide hit him, also killing his colleague who had rushed to save him.
The more his concentration increases, the more he does not perceive his sense of smell
Although it is easily recognisable, the gas has two characteristics that make it insidious. The first is that the more its concentration grows, the more our sense of smell stops perceiving it: as if the nose were anesthetized.
The second is that, being heavier than air, it tends to accumulate in the lower parts of tanks and basins. To save themselves, those who are hit should make the effort to climb back up. However, climbing the stairs in a suffocating condition may be too difficult a task.
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– 2024-05-07 03:17:37
