Among the hypotheses being examined on the causes of the death of the five workers while they were working on the sewerage network of Casteldaccia, the suffocation by hydrogen sulphide was advanced. Hydrogen sulfide or hydrogen sulphate (chemical formula H2S) is a lethal poisonous gas if present in some specific conditions (e.g. wastewater treatment plants, waste, etc.). It is recognizable by the unmistakable smell of rotten egg. There can be no question of risk for the general population. But there are areas of Italy, especially of volcanic origin, where the gas could constitute a greater danger.
What are the symptoms caused by hydrogen sulfide
H2S irritates the mucous membranes of the body and the respiratory tract, among other things. Following exposure, short-term, or acute, symptoms may include headache, nausea, seizures, and eye and skin irritation. Injuries to the central nervous system can be immediate and severe following exposure. It acts similarly to cyanide. At high concentrations, just a few breaths are enough to induce unconsciousness, coma, respiratory paralysis, convulsions and even death.
How to recognize gas
But it is easily recognisable. “Indeed. Hydrogen sulfide, that’s what smells like rotten eggs. And this can often be the case a very qualitative indicator of environmental concentrations classics that can indicate the presence of this gas”, he explains Gaetano Settimofirst researcher of the Environment and Health Department of the Higher Institute of Health and Coordinator of the National Indoor Pollution Study Group.
«Until we smell, it means that our olfactory system, the epithelium, is still able to recognize the possible presence of the gas. Unfortunately, when certain concentrations are exceeded our olfactory system no longer hears because he is continually stressed, he becomes a bit dazed by concentration. So not smelling rotten eggs often means finding yourself in dangerous situations.”
Where hydrogen sulfide is found in the environment
«Hydrogen sulfide is a classic pollutant from natural sources. If we get close to what could be thermal springs, we smell the classic smell of rotten eggs. Sulphurous waters, for example, bring with them this characteristic of rotten eggs”, explains the expert.
Is there a risk for the general population? «Some areas of our country are of volcanic origin. And clearly this geological feature often makes itself felt, through what we call intrusion of endogenous gases from the subsurface. And therefore the presence of carbon dioxide (CO2), hydrogen sulphide (H2S) and sulfur dioxide (SO2) in these areas can represent a risk for the population who resides in these environments for a much longer period – underlines Settimo -. This is a vulnerable population and therefore these are substances in those territories that need to be paid attention to. Precisely to know the concentrations that vary throughout the day, because these phenomena have been studied for several years».
«Often the main problem is that at night, by decreasing atmospheric pressure, there is a natural phenomenon of rising of these gases. So there is a call towards the homes that have been built on these territories.”
The limits established by the World Health Organization
Are there any guide values for exposure? «The World Health Organization has identified reference values on short-term concentrations over 30 minutes and as an average over 24 hours: the short-term concentration is 7 micrograms per cubic meter. The daily concentration is 150 micrograms per cubic meter. While, in professional work environments, in the current Legislative Decree 81/08 there is no VLEP professional limit value”, replies Settimo.
«The problem arises when these concentrations begin to grow and reach values that can lead to acute exposures, as may have happened to the poor workers of Casteldaccia, who expose the worker to effects which can be, as happened, unfortunately lethal.”
The health effects
What are the effects on the body? However, can prolonged exposure to low levels cause a series of disorders? «Yes, normally the bulk of the health effects occur with exposure to concentrations already higher than those we have indicated, foreseen by the World Health Organization – explains the first ISS researcher -. The effect of this exposure, which occurs mainly in what are defined as confined environments, therefore tanks, cisterns, pipelines, leads almost immediately, when 2 or 3 breaths have already been taken, to respiratory and cardiac failure. There is no breathing, so you can suffer from pulmonary edema and the famous cyanosis. To be clear, you don’t even have the ability or readiness to walk away because it is an acute effect. Unlike what can be chronic long-term exposures, but at decidedly lower concentrations”
What precautions should be taken at work
How do you normally take precautions against the possible presence of hydrogen sulphide when working? «When these jobs are done in environments that are confined, I must undergo training and normally I must have specific detectors for sulfurized idogrene and personal protective equipment (PPE), like it was done in the mines with the famous little bird. Normally I have to be notified with light or sound signals, that that is air that can pose health risks to me”, adds the expert.
Don’t you have to wear special protection? «Depending on what may be some specific activities, the operator can be immediately equipped with self-contained breathing apparatus. But there is a whole lot of training linked to the characteristics of the work site and the type of activity, to the length of time the operator must stay in a certain environment in which he must work”.
Training
Normally chi carries out this type of intervention at work should be informed and trained on the risks what can he encounter? «Absolutely yes, and he should always have these detection systems and specific PPE available. Before entering any environment you need to use these systems to understand what the gas concentrations are.”
Areas at risk and ripple effect
Are censuses of risk areas carried out? «The areas at risk for professionally exposed workers, so we are not talking about the general population, it is all those activities that unfortunately exact a very high price in terms of human lives every year. They are, as we were saying, the famous confined spaces. They are the tanks, the cisterns where there is no dilution phenomenon, that is, all these gases accumulate inside, therefore reach concentrations that unfortunately become lethal and clearly the operators who have no training or preparation, who are not equipped with personal protective equipment, who do not know the lethality characteristics of these substances, unfortunately, let’s say, suffer.
«Because hydrogen sulfide it doesn’t give you a chance, that is, you immediately lose consciousness. And therefore a “chain effect” also occurs among the rescuers: the first dies, the second dies to help the first, the third dies to help the first and the second” Settimo concludes. As happened, unfortunately, in Casteldaccia.
