Methyl mercaptan, also known as methanethiol (CH3SH), is one of the fragrances of human flatus. Interestingly, it has been added to natural gas since 1937 in response to the third worst-ever disaster in the history of Texas. One type of natural gas is methane, and like many of the small alkane molecules, it has no smell, meaning that leaks are hard to detect. That can lead to a dangerous situation since methane is highly flammable as was demonstrated by a tragic explosion in Texas in 1937 that killed 294 people, mostly children, 1/3 of whom were in grades 5 to 7. Since then, smelly methanethiol has been added to natural gas so that leaks can be detected before the air becomes flammable. Methanethiol is toxic, but our noses are sensitive to very low and non-toxic concentrations, as low as 1 part per billion. So, it takes very little to act as a protective alarm.
Unfortunately, too often it takes a disaster for us to get off our butts and instill safeguards. In the case of the New London School accident in Texas, the methane that was used to heat the building had been accumulating under their building. (That neck of the woods experiences overnight lows of 3 to 8 degrees Celsius between November and March, so heating was necessary.) A nearby oil company had no use for the natural gas it produced as part of petroleum refining and the school district had decided to save money and get their gas from the company's residue line tap.
Unfortunately, the line leaked methane, and because the school had been built on a slope, the gas had accumulated in a large crawl space under the building. From there the gas slowly leaked into the school. Although methane was additive-free and therefore odorless at the time, children had been complaining of headaches, but the complaints were ignored. Then one day, a sander was turned on. It ignited the methane-rich air. The flame spread to the reservoir. The combustion within the confined area led to such a large pressure increase that it lifted the school's roof and expanded its walls. The explosion was heard within a four-mile radius. Gravity and inertia then combined to smash the structure. A concrete slab was hurled smashing a car that was 200 feet from the school. The debris and concrete from the giant collapse killed almost 60% of the people in the school.
Turn the clock ahead to the present time and methanethiol does not help us with preventing the disasters of climate change. Like the children's headaches, we are getting plenty of warnings, but they are ignored by too many of us. We often complain about the appeal-to-nature fallacy when it comes to herb-treatments for colds or foods free from preservatives, but it applies equally to so-called "natural gas". It might be a better alternative than coal, but such bragging is like the 2nd last team in baseball gloating about its position while pointing to the basement-dweller.
From a molecular perspective, methane (CH4), when used as fuel, releases our principal greenhouse gas, carbon dioxide, in a one-to-one ratio. But methane is about 18 times better at absorbing infrared radiation than carbon dioxide. Luckily its residence time in the atmosphere is only 9 years, but concentrations in the global atmosphere have gone up by 18% in the last forty years. So, the warming effect hasn't gone away as we've more than replaced any methane that has oxidized back to carbon dioxide.
Why has it accumulated? It gets released by the digestive system of cattle; by melting permafrost, and by leaks in methane gas lines. It's been estimated that such leaks are 3 times more pervasive than what's reported by the EPA in the United States. Replacing natural gas, coal and diesel fuel with solar and hydropower-sourced hydrogen is not risk free either.
Hydrogen is also prone to leaks. In fact, it's better at it, being a smaller and lighter molecule than methane. It can also act as a greenhouse gas, albeit indirectly. In the atmosphere, under the influence of sunlight ozone and water vapour react to produce highly reactive hydroxyl radicals that can destroy methane. This is why the residence time of methane in the atmosphere is much shorter than that of carbon dioxide. However, hydroxyl radicals can also react with hydrogen to produce water meaning that there will be less hydroxyl to eliminate methane, which will then stick around longer.
In the case of the Texas tragedy, headaches were a warning not acted upon. We should learn from the past. Knowledge of the chemistry of the atmosphere now explains how greenhouse gases are building up. We are being warned. We need to take heed.
Enrico Uva is a retired chemistry teacher who still enjoys learning chemistry, other sciences and mathematics.聽
