On March 31, 2025, an explosion at the Cerredo mine in Degaña, Asturias, has resulted in the tragic loss of five miners, with an additional four sustaining various injuries.

Investigators from the Mine Rescue Brigade and Judicial Police are focusing on the explosion of a methane gas pocket as the primary hypothesis behind the incident, as confirmed by Adriana Lastra, the Government Delegate in Asturias.

Methane, known locally as grisú, is regarded as a significant hazard in mining operations.

Comprising over 90% methane, the gas is highly flammable and can form explosive mixtures with air.

It poses a substantial suffocation risk due to its oxygen-absorbing properties, leading to instant asphyxiation for those exposed without adequate ventilation.

Grisú is generated concurrently with coal and can also contain other gases such as carbon dioxide or carbon monoxide.

Generally, it is odorless and requires specialized equipment for detection.

Accumulation of grisú in mining tunnels can occur due to the decomposition of organic materials or natural release mechanisms from coal seams.

Typically, the gas exists in small molecules bonded to coal, which continuously release into the atmosphere.

Maintaining grisú concentrations below 1% to 1.2% is critical in preventing hazardous conditions.

Asturias and León are known for their coal deposits, where grisú is more prevalent compared to anthracite or lignite mines.

The explosive potential of grisú is particularly concerning, as even a minor spark or heat source can trigger catastrophic explosions.

To mitigate risks associated with grisú, mining operations implement continuous monitoring and ventilation systems designed to prevent gas accumulation.

Mining facilities are equipped with ventilatory systems to manage gas dispersal, alongside grisómetros that track gas levels.

Additionally, proactive measures such as degasification work involve creating boreholes to allow controlled release of methane.

Workers are also equipped with methane detectors and self-rescue devices, which provide limited oxygen supply for more than 30 minutes in oxygen-depleted environments.

However, such equipment primarily addresses asphyxiation risks and does not prevent potential explosion hazards.

Historically, miners utilized canaries as an early warning system for dangerous gases like grisú and carbon monoxide.

These birds, being more sensitive to toxic gases, would exhibit distress or perish before miners experienced harmful effects, thus providing critical time for evacuation.

Use of canaries continued until the late 20th century, when they were replaced by mechanical and then electronic gas detectors in Spanish coal mines, especially prevalent in Asturias and León.

Notable grisú-related disasters include the San Nicolás mine accident in Mieres on August 31, 1995, which claimed the lives of 14 miners due to a grisú explosion, resulting in a fire that complicated rescue operations.

Similarly, the Emilio del Valle mine tragedy in León on October 28, 2013, resulted in the immediate asphyxiation of six workers due to grisú displacing oxygen.

The most devastating incident occurred on November 3, 1975, at the Figols mine near Barcelona, where an explosion killed 30 miners.