The funeral for Senior Sergeant Lyn Fleming is in Nelson today and California remains under critical fire threat. Video / NZ Herald, AFP
Above the roaring fires devastating parts of Los Angeles is an incongruous sight: air tankers dropping gallons of bright red and Barbie-pink slurry over forest, homes, cars, and anything else that might lie in the blazes' path.
The substance, vivid against the grey smoke and charred landscape, is fire retardant – much of it a product called Phos-Chek that has been used by the US Forest Service since the 1960s.
“You can see it so easily ... it’s amazing stuff,” says Jason Colquhoun, a 53-year-old pilot with HeliQwest, a charter helicopter company specialising in putting out fires.
But over the past week it’s been dropped on residential neighbourhoods at an “unprecedented” scale, says Daniel McCurry, an associate professor of civil and environmental engineering at the University of Southern California.
That’s led to one overwhelming question: how safe is it?
Sold by fire protection equipment supplier Perimeter Solutions, Phos-Chek is a mixture of primarily ammonium phosphate or ammonium polyphosphate – fertiliser – with additives such as iron oxide – rust – to give it colour.
A firefighting aircraft drops the fire retardant Phos-Chek near homes during the Palisades fire. Photo / AFP
Its bright hue – which, Perimeter told AFP, is actually all the same colour, but can look different depending on time of day, lighting, smoke and so on – helps pilots as they try to ensure overlapping, unbroken lines around the fires, Colquhoun explains.
When pilots drop water from the air, he says, they must search for “the shine and the darkness” to know where to make the next drop. The vivid retardant, however? “So much easier to spot.”
The other advantage compared to water: it keeps working, even after the water it is mixed with evaporates, McCurry says.
Thickeners add viscosity and help ensure it doesn’t drift off target, adds McCurry, who led recent research into heavy metal content in such retardants.
It comes in a powder and is mixed in – essentially – giant paddling pools, before being loaded on to planes and helicopters for coordinated drops, Colquhoun says.
He gave an enthusiastic “Oh yeah” when asked by AFP if it works.
It does so by forming a non-flammable carbon coating, Perimeter explained in a statement to AFP. The water in the slurry boils off, helping to quench the flames; and the retardant works until it is diluted by rain – when it fertilises the ground.
McCurry said he has seen photos “where a brush fire burned right up to a Phos-Chek line and then stopped,” but expressed some caution.
He cited a former firefighter as telling him that in a high-intensity fire it’s “not much use”, and said that the high winds which have fanned the fires in Los Angeles may have limited its effectiveness.
The Forest Service said it only uses retardants that “meet the Environmental Protection Agency’s criteria for being ‘practically non-toxic’ to mammals, including humans, and aquatic species”.
The charred remains of homes destroyed by the Palisades fire in the Pacific Palisades neighbourhood of Los Angeles. Photo / AFP
It prohibits drops in waterways and areas home to vulnerable species – unless the fire is threatening human life or public safety, and the retardant could be “reasonably expected” to stave off that threat, spokesman Wade Muehlhof told AFP.
But accidents do happen, he said, “whether through wind drift or an inadvertent drop”.
The service says it phased out Phos-Chek’s older formulation, LC95 – which McCurry’s study showed had high levels of heavy metals that can contaminate drinking water – nationwide as of December 31.
Now it uses a new, less toxic formulation called MVP-Fx, it says. Phos-Chek contains no so-called forever chemicals and no substances “that are known to cause cancer or other harms” under California law, Perimeter added.
McCurry says the Forest Service has been successfully sued in the past on environmental grounds, and that Phos-Chek is “likely not harmless to the environment” now.
“On the other hand, the human health impact is still a little unclear,” he says.
He says it would take “a lot” of retardant to poison, say, a reservoir.
“However in the last week we’ve seen it dropped on neighbourhoods at an unprecedented scale,” he continues, adding that it’s more often used further from populated areas, or in lower amounts.
