Can Dry Ice Put Out Fires That Burn Underground?

Imagine a fire that appears to have been extinguished, only to keep burning beneath the surface. That’s what makes peatland fires so difficult to control. And in Indonesia, an unusual substance has entered the conversation: dry ice.

Indonesia is experiencing one of its worst wildfire seasons in over a decade. The forest and peatland fires have sent thick smoke into neighbouring countries, increased respiratory illnesses and left large areas of Southeast Asia covered in haze.

Singapore and Malaysia have been particularly affected, while the smoke has also reached Timor-Leste and the Philippines. Schools have closed in affected areas, flights have been disrupted and people are struggling with dangerously polluted air.

According to independent forest monitoring platform Nusantara Atlas, more than 895,000 hectares of land had burned across Indonesia by the end of August 2026. The platform also recorded more than one million wildfire hotspots by mid-October. These hotspots are satellite detections of heat, not necessarily individual fires.

Much of the concern is centred on the peatlands of Borneo and Sumatra, where fires burn very differently from those in ordinary forests.

Can dry ice put out an underground fire?

As videos of Indonesia’s smoke-covered cities circulate on social media, authorities are trying different ways to control the situation. A prolonged drought, aggravated by severe El Niño conditions, has made forests and peatlands across Sumatra and Borneo especially vulnerable to fire.

Indonesia has already used cloud seeding and water bombing to tackle the fires. Now, authorities are experimenting with dry ice to reduce the haze. According to reports, the trial involves dispersing 1.5 tonnes of dry ice from an aircraft over Palembang in South Sumatra.

There are two different ways dry ice is being considered in such situations: applying it directly to burning peat to cool and suppress combustion, or dispersing it into the atmosphere to influence atmospheric conditions.

One aims to tackle the fire itself, while the other attempts to manage the haze.

Indonesia’s proposed aerial trial falls into the second category, and whether it can provide significant relief remains uncertain.

How does dry ice work on a fire?

Dry ice is solid carbon dioxide. Unlike ordinary ice, it doesn’t melt into water but turns directly into gas. At around −78.5°C, it is extremely cold.

When applied directly to burning peat, dry ice absorbs heat and releases carbon dioxide, which can reduce the oxygen available for combustion.

A team of researchers led by Zhang and Huang tested four agents on smouldering peat in a laboratory: water, ice, dry ice and liquid nitrogen.

Dry ice performed best under the experimental conditions. It required the least mass among the tested agents to achieve comparable suppression and provided the longest effective cooling duration, lasting up to 175 minutes.

Liquid nitrogen cooled the peat rapidly, but its effect was short-lived, allowing temperatures to rise again. Ordinary ice also helped, although dry ice was more effective in the tests.

The findings suggest that dry ice could be useful for controlling underground peat fires. However, laboratory experiments are different from fighting fires spread across vast areas of land.

What is peatland, and why are its fires so hard to put out?

Peat is soil made up of plant material that has only partially decomposed over thousands of years in waterlogged conditions.

Borneo and Sumatra have vast peatlands that become especially vulnerable to fire during the dry season. Land clearing for crops such as palm oil, along with drainage, has lowered water levels in many areas and dried out the soil, increasing the risk of fire. The problem is that the fire isn’t always apparent on the surface.

Unlike a typical forest fire with visible flames, peat fires can continue smouldering through layers beneath the ground. These fires are difficult to put out because they are concealed and can reignite even after the surface appears safe.

In some conditions, smouldering can continue for weeks or months, spreading slowly through the underground material. Water is the obvious solution, but it takes a lot. In laboratory tests, Papuan peat required approximately 4.22 litres of water per kilogram to extinguish the fire, while Jambi peat required around 3.81 litres per kilogram.

Water can struggle to reach every burning pocket because it doesn’t always spread evenly through the porous peat. Even when the surface is wet, some underground layers may remain hot enough for the fire to continue.

This is why researchers are investigating alternatives such as dry ice.

Is dry ice the solution?

The research is promising, but there’s still a considerable difference between extinguishing peat in a laboratory and controlling fires across hundreds of thousands of hectares.

Getting dry ice to reach the burning layers underground would be difficult. Its effectiveness on such a large scale has not yet been established.

Indonesia’s aerial dry ice trial is also aimed at managing atmospheric conditions rather than directly extinguishing the fires beneath the surface. Even if it provides temporary relief from the haze, the smoke will continue as long as the fires remain active.

There is also a larger problem that dry ice cannot solve.

Peatlands naturally hold enormous amounts of water. When they are drained for agriculture or land development, the soil becomes much more vulnerable to fire. Keeping peatlands wet and restoring damaged areas can significantly reduce the risk.

When we think of a wildfire, we imagine large flames consuming forests. But in Indonesia, some of the most difficult fires to fight are the ones we cannot see.

Dry ice may offer another way to tackle them, and the early research is encouraging. But preventing peatlands from drying out remains one of the most effective ways to reduce these fires in the first place.