In the tale of the three little pigs, the third pig's brick house withstood the wolf's blustery breath. Had there been a wildfire in the woods, the brick house would have also fared better than the wood and straw houses the pig's brothers made. For that matter, it would have held up better than most modern homes.
Today's houses, made of engineered wood and full of synthetic materials, burn hotter and faster than homes built a few decades ago. This can lead to devastating loss of property and life as more people build closer to wildland areas, creating urban-wildlife interfaces packed with trees and other flammable materials.
Flame retardants, which prevent and slow down combustion, provide precious minutes for people to escape or for help to arrive before a small fire turns into a roaring blaze. Unfortunately, some of these chemicals pose a risk to human health-they have been linked to cancer, neurological damage, and hormone disruption-and to the environment. Since the early 2000s, some flame retardants have been banned and removed from the market in many countries. That doesn't stop their illegal and legal use globally. New chemistries that take their place can sometimes bear similar risks but continue to be used because of inadequate testing and varying regulations.
Unlike wildfires, the flame-retardant industry moves slowly. "Some technologies that are in use today were in use 20 years ago," says Alexander B. Morgan, a chemist and fire safety researcher at the University of Dayton. "Flame retardants are better now than they were in the '90s, but there is a lot of room for improvement."
Researchers around the world showcased their latest developments-from spray-on water-based flame retardants to those made from wine industry waste and seed husks-at the 20th European Meeting on Fire Retardant Polymeric Materials, held in Madrid in early June.
Finding a flame retardant that meets fire, health, and environmental safety standards is not easy. Every material-cotton, plywood, and each of the dozens of synthetic polymers-burns differently and needs a unique flame-retardant chemistry. Often, there is no benign option that resists fire without affecting the polymer's performance.
"You want to make flame retardants more effective so that you need less of them to avoid altering the beneficial properties of the polymer," says Jaime Grunlan, a mechanical engineer at Texas A&M University. "You want to be very effective with very little toxicity. It's complicated, but that's the dream."
Flame retardants are not new. Humans started using asbestos to make fireproof clay pots and textiles thousands of years ago. Ancient Egyptians infused wood with aluminum salts to slow its burn rate. Natural materials such as wool, silk, and leather that humans have used for centuries inherently resist burning.
Society's shift to synthetic materials fueled the need for complex, flame-retarding chemicals. Between 150 and 200 commercial flame retardants are available today. They are used in electronics, furniture foam, insulation, paints, textiles, wire sheathing, and many other products. About 3.5 million metric tons of flame retardants per year are used globally, and 85% goes into plastics, according to Pinfa (the Phosphorus, Inorganic and Nitrogen Flame Retardants Association), a global consortium of over 40 makers and users of flame retardants.
A flame retardant's main job is to stop the feedback loop between fuel and oxygen to starve the fire. Some release inert gases such as nitrogen to dilute the oxygen in the flame. Intumescent systems form a char layer that keeps oxygen from getting to the flammable material.
The first modern flame retardants were based on brominated and chlorinated organic molecules, which work by scavenging free radicals that are key for combustion. After facing fire from health and environmental groups because of their toxicity, some halogenated compounds were restricted in the European Union and in some US states.