Flame retardants (FRs) keep many of the everyday objects in our lives safe, but they also pose significant health and environmental hazards. In this must-read Q&A, LGC Standards’ Global End Market Manager for Environment and Forensics, Dr Kelly Cheshire, brings you up to speed with the fast-changing flame retardants picture around the world. We cover the most common FRs, best practice in flame retardant testing - and how regulatory change, green technology, and environment-friendly design are all currently shaking up the FR industry.

What are flame retardants, and why are they important in everyday products?

Flame retardants are chemical additives or treatments which are incorporated into, or applied onto, materials - including polymers, textiles, foams, and electronics. They’re there to inhibit, delay, or suppress the ignition and spread of fire. And they’re critical for safety: by slowing down combustion, they give people time to escape, reduce heat release rates, and prevent - or delay - fire propagation from becoming catastrophic. In many products - especially in electronics, construction materials, furnishings, and transportation - they are essential in meeting fire safety standards and reducing the risk of fire.

Which are the most common types of flame retardant?

There are four main classes of flame retardants – or FRs for short. The first is halogenated flame retardants, and especially brominated or chlorinated products, which are very effective at low loadings, or concentrations. They work by releasing halogen radicals to quench flame propagation reactions in the gas phase.

The next major class of FRs is phosphorus based – or organophosphorus - retardants. These act in the condensed phase by promoting char formation, or via phosphoric acid radicals interfering with flame chemistry. They are widely used, especially in more environmentally friendly formulations.

Next, we have mineral, or inorganic, retardants like aluminium hydroxide (ATH), magnesium hydroxide (MDH), antimony trioxide, and metal phosphonates. These are often lower cost, and nonhalogenated, but they require higher loadings – and that can affect the product’s physical properties.

Lastly, there are intumescent systems and synergistic combinations, which often combine phosphorus, nitrogen, or inorganic fillers that form an expanding protective char when exposed to heat.

Of course, choosing which type is optimal will depend on the material substrate – for example, is it plastic, foam, or textile? – as well as the fire performance required. Then there are cost constraints, regulatory pressures, and other property trade offs to consider.

Can you tell us more about how flame retardants affect material properties?

Sure. High loading of fillers (e.g. minerals) can make materials more brittle. And some FRs may leach, migrate, or degrade when exposed to UV light, heat, or humidity, which affects long-term performance. Additives can also affect a product’s transparency, colour stability, or surface finish, and so flame retardants are often chosen in order to balance fire performance with mechanical and aesthetic considerations.

What are the most common flame retardancy tests?

Well, there are many! But I’ll give you my top five, and try to explain why each one is important.

Let’s start with UL 94, which is important for classifying plastic parts for electronics, enclosures, and consumer products. It measures how a small flame applied to a plastic sample behaves: for example, does it self-extinguish? How long does it burn for? And what is the dripping behaviour?

Then there’s LOI – or Limiting Oxygen Index – which determines the lowest oxygen concentration in which a material will support combustion. A higher LOI indicates better flame resistance, and so this test is useful for ranking materials under controlled conditions.

Next, Cone Calorimeter tests, like ISO 5660 and ASTM E1354, give a realistic view of how a material behaves under severe fire exposure. They measure heat release rate (HRR), total heat released (THR), time to ignition, and mass loss, as well as smoke generation.

Meanwhile, smoke density and toxicity tests like ASTM E662 and ISO 5659 measure the amount and density of smoke generated, and possible toxic gas emissions during burning. And of course, they are critical for human safety in fire scenarios.

Last but not least, glow wire and ignitability tests like IEC 60695 measure whether material for electrical or wiring components will ignite, or continue to glow dangerously, when exposed to hot wires.

I’ve chosen these because each test targets a different aspect of fire performance: ignition resistance, flame spread, heat release, smoke production, and durability under thermal stress.

When should we retest materials or products for flame retardancy, and what are the typical failure points in these tests?

When to retest depends on several factors: for example, when significant formulation changes are made, or when raw material suppliers change, as well as when regulatory updates demand testing under new or stricter conditions.

Retesting is also going to be needed in response to failed lots, customer complaints, or ageing and degradation concerns. And of course, annual, and other regularly scheduled retesting programmes are an essential part of any organisation’s quality control.

When we talk about common failure modes, we’re often looking at sustained burning, a failure to self-extinguish, or excessive flaming drips that ignite cotton below (when using UL 94). And during Cone Calorimeter tests, we often encounter high heat release or rapid flame spread. We might also expect to find excess production of smoke or toxic gas, failures related to ageing or exposure, as well as delamination, cracking, or damage under thermal stress.

Are there any upcoming regulatory changes we should be aware of?

Yes, there is increasing regulatory pressure on halogenated flame retardants - especially brominated and chlorinated ones - due to their toxicity, persistence, and concerns about bioaccumulation. For example: some jurisdictions are already proposing, or enacting, tighter restrictions or bans on certain deca BDEs, HBCDs, and PBDEs.

There is also more of an emphasis on developing sustainable, or non-halogenated, alternatives - and stricter requirements under REACH for hazard data, use restrictions, and substitution. In addition, green building certifications like LEED and BREEAM increasingly reward low toxicity, sustainable materials. All of these factors are increasing demand for safer flame retardants.

OK, so what are the sustainable/halogen-free alternatives we should be considering?

There are already alternative FRs available that are often less toxic, or more environmentally benign, than traditional halogenated systems - although sometimes at the cost of higher loadings or performance trade-offs. Among the alternatives that companies should be considering are phosphorus-based, nitrogen-based, or silicon-based flame retardants - and mineral FRs like aluminium hydroxide and magnesium hydroxide.

Then there are intumescent systems which expand to insulate when heated, as well as nanocomposite or nano fillers with synergistic flame retardant behaviour, such as layered silicates and graphene oxide. Finally, they might also want to consider using bio based FRs made with renewable feedstocks, and reactive products that are covalently bound into a polymer matrix to reduce migration.

Apart from choosing alternative materials, how can the industry address the wider environmental and health concerns about FRs?

Thankfully, there are several other routes to becoming greener, such as taking a “benign by design” approach that embeds safer chemical design principles and better toxicity screening. There’s also considerable scope for collaboration between industry and research institutions on sustainable flame retardancy, as well as for integrating health and environmental impact into flame retardant selection through Lifecycle Assessments (LCAs). Looking at the longer term, we can do more to improve FR recycling and recovery strategies with the aim of reducing environmental release. And we can step up the monitoring and detection of FRs in environmental media like soil, dust, sediment, and biota.

Authors

Dr Kelly Cheshire

Global End Market Manager

Andy Blizzard

Copy Writer