A spray of red color falls from a plane over a burning hill. Although it looks like a gaseous cloud, it is long-lasting retardant liquid: a new generation substance that is beginning to be applied on a large scale in forest fires inside and outside Spain as a last barrier against the advance of the fire. “The soaked area becomes sticky, so when the flame arrives it cannot burn it. The relationship between fire, air, and fuel does not occur,” explains Federico Grillo, spokesperson for the College of Forest Engineers.
“In the case of active firefighting, the usual practice is the use of retardant in what is known as indirect attack. It is generally applied aerially, advancing along the fire front,” adds Xavier Vaquer, vice president of Perimeter Solutions, parent company of the Asturian company Auxquimia and a world leader in the retardant sector. Founded more than 50 years ago, it now leads sales of red water in Spain, although 90% of its sales come from exports. Its retardants are the only ones currently certified by entities such as the U.S. Forest Service in the United States and CEREN (Center for Testing and Fighting Forest Fires, by its French acronym) on the other side of the Pyrenees.
This liquid has become a fundamental tool in an emergency context like the one Spain has been experiencing in recent weeks. “It creates a firebreak barrier that allows stopping the advance and containment of the fire,” says Vaquer. So far, the fire has devastated 80,000 hectares between Madrid, Ávila, and Toledo, and another 9,300 in Castellón. Just a few days ago, it burned 32,000 in La Mierla (Guadalajara). Four of the five most severe fires in Spain’s history have occurred in 2025 and 2026.
“Something this big had never happened before. Our country has a lot of experience, which makes us quite efficient, but a historic episode with such great force demands a very good strategy. And in these extraordinary situations, there is always room for improvement,” Grillo acknowledges the innovative contribution of retardants.
“It requires a certain level of anticipation in planning, preparation, training, and investment of the necessary resources for its proper use in forest fire extinction,” admits the vice president of Perimeter Solutions, who finds it hard to find a slot in his schedule amid this firestorm. “During the fire season and especially during the fight and extinction of active fires, the workload and demand are usually high, as we must guarantee the capabilities of our clients in fighting forest fires,” he points out.
The horror caused by seeing the environmental disaster contrasts with the relief caused by seeing the deployment of forest brigades. Over these days, we have seen how the retardant works. Its red color comes from a pigment based on iron and oxide. It is not arbitrary either: it allows marking the area where it was dropped to better identify from the sky the zones already sprayed. For the manufacture of this product, Vaquer explains, it is necessary to add several active compounds used in other agricultural applications to the water, as well as components that improve the product’s efficacy and stability in the long term.
For its effective application, the water bomber plane must head to an aerodrome or airport, park next to pools equipped with a motor pump – which stirs the water to prevent the product from settling – and proceed to inject the liquid, explains the forest engineer. Vaquer highlights that the retardant works long-term in the prevention and protection of strategic or critical areas, as it takes several months to be washed away by precipitation. “It remains adhered to the vegetation, completely safe and harmless, and will only react in the presence of the high temperatures caused by the fire,” he assures.
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“Phosphate and ammonium polyphosphate retardants are components of fertilizers and the amount is very small,” Grillo assesses the degree of environmental impact, although he warns that spraying them in places like lagoons or streams is not recommended, as they can degrade the water, cause algae blooms, and be toxic to fish, amphibians, and other animals.
The United States, Canada, and Australia – scenes of some of the worst environmental catastrophes caused by fire in recent centuries – are the countries that use retardant the most, although its use is increasingly spreading to more countries. France has introduced an Airbus A400M capable of dropping up to 20,000 liters of ‘red water’. Spain is not falling behind, although for now it prioritizes other techniques. “There is no definitive solution; each tool has its advantages and disadvantages,” warns Grillo. “The combination of different techniques opens up a range of possibilities,” he adds.
Besides Auxquimia’s product, last year another with similar characteristics called Ecofire Fighting appeared. Its creator, César Sallén, appeared on some TV programs to show how a liquid that promises to be 30 to 40 times more effective than water works. Although it has undergone studies such as the INIA-CSIC one, which certified its effectiveness as an extinguisher, it does not yet have the same scientific backing as the competition.
The major drawback of the retardant is its high cost. “We are talking about million-euro figures to put out a fire: a 1,000-liter drop can cost between 600 and 1,000 euros,” points out the spokesperson for the College of Forest Engineers. Also, as this expert argues, foam is cheaper since it requires a very low percentage of concentrate diluted in water compared to retardant. However, Vaquer clarifies that investing in one product or the other will depend on the strategy to be implemented. “Both are complementary and effective in their application field,” he emphasizes. “They have completely different mechanisms of action. Foams help improve the extinguishing capacity of water, while retardants prevent the fire from generating or spreading. They break the fire triangle cellulose-oxygen-heat,” he specifies.
Likewise, according to the forest engineer, the use of this innovative technology requires more complex logistics. “We would lose a lot of time going to an airport with a helicopter to load. In the case of amphibious aircraft that collect water from reservoirs, the flight approaches the water, reloads, and drops again,” he reviews.
However, the Airbus A400M used this week in France has a greater capacity than other planes. For now, it is the only active model, despite Spain announcing its acquisition in May and its manufacture involving the Spanish Air Force and the Ministry of Ecological Transition. Four months ago, the Prime Minister, Pedro Sánchez, announced that Spain would have 15 Airbus A400Ms with firefighting kits, but their systems are still under development and certification.
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