FIRE SAFETY and FLAME RETARDANTS

Statistics suggests that India leads the global chart in fire accidents where more than 25000 people die in India every year and this is the second cause of unnatural deaths, after road accidents.

In fire accidents, people die or get injured because of three reasons –

1. Burns in the flame
2. Suffocation in smoke due to its high density
3. Inhaling of toxic gases generated in the fire

Flame retardants is an important passive fire protection measure and helps in reducing the impact of fires affecting people, property and the environment. They are added to or treat potentially flammable materials, including textiles and plastics. The term “flame retardant” refers to a function, not a family of chemicals. A variety of different chemicals, with different properties and structures, act as flame retardants and these chemicals are often combined for effectiveness. It is important to understand what type of flame retardants are used, toxic or non-toxic, to ensure maximum fire safety.

Flame retardants are added to different materials or applied as a treatment to materials (e.g., textiles, plastics) to prevent fires from starting, limit the spread of fire and minimize fire damage. Some flame retardants work effectively on their own; others act as “synergists” to increase the fire protective benefits of other flame retardants. A variety of flame retardants is necessary because materials that need to be made fire-resistant are very different in their physical nature and chemical composition, so they behave differently during combustion. The elements in flame retardants also react differently with fire. As a result, flame retardants have to be matched appropriately to each type of material.

Flame retardants work to stop or delay fire, but, depending on their chemical makeup, they interact at different stages of the fire cycle. To better understand how flame retardants work, it’s helpful to understand the fire cycle:

• Initial ignition source can be any energy source (e.g., heat, incandescent material, a small flame).
• Ignition source causes the material to burn and decompose (pyrolysis), releasing flammable gases.
• If solid materials do not break down into gases, they remain in a condensed phase. During this phase, they will slowly smolder and, often, self-extinguish, especially if they “char,” meaning the material creates a carbonated barrier between the flame and the underlying material.
• In the gas phase, flammable gases released from the material are mixed with oxygen from the air. In the combustion zone, or the burning phase, fuel, oxygen and free radicals combine to create chemical reactions that cause visible flames to appear. The fire then becomes self-sustaining because, as it continues to burn the material, more flammable gases are released, feeding the combustion process.

When flame retardants are present in the material, they can act in three key ways to stop the burning process. They may work to:

Development of a fire

1. Disrupt the combustion stage of a fire cycle, including avoiding or delaying “ flashover,” or the burst of flames that engulfs a room and makes it much more difficult to escape.
2. Limit the process of decomposition by physically insulating the available fuel sources from the material source with a fire-resisting “char” layer.
3. Dilute the flammable gases and oxygen concentrations in the flame formation zone by emitting water, nitrogen or other inert gases.

While an ever-evolving list of new products—from hair dryers and small appliances to laptops and flat-screen televisions—is incorporated into our homes, offices and commercial environments, we seldom think about how the products are made. Flame retardants provide consumers with a critical layer of fire protection and are vital to reducing the risks associated with fire.

Today, flame retardants are used predominantly in four major areas:

Electronics and Electrical Devices

• Television and other electronic device casings, Computers and laptops, Telephones and cell phones, Electronic circuit boards
• Refrigerators,Washers & dryers, Vacuum cleaners, battery charger
• Electrical and optical wires and cables, Small household appliances

Building and Construction Materials

• Electrical wires, cables, Insulation materials, Paints and coatings
• Structural and decorative wood products, Roofing components, Composite panels and Decorative fixtures

Furnishings

Natural and synthetic filling materials, textile fibers, Foam upholstery, Curtains and fabric blinds, Carpets

Transportation (Airplanes, Trains, Automobiles)

• Overhead compartments, Seat covers and fillings, Seats, headrests and armrests
• Roof liners, Textile carpets, Curtains, Sidewall and ceiling panels
• Internal structures, including dashboards and instrument panels
• Car bumpers, Stereo components, GPS and other components 

Experts recognize the use of flame retardants as essential to stopping or slowing the spread of fire. Flame retardants are used to prevent ignition by increasing the threshold required to start a fire; reduce the spread of fire; and delay flashover, the “fireball” that can quickly occur when the combined heat and the release of flammable gases cause automatic combustion. Delaying flashover reduces the rate and intensity of burning and increases the amount of time people have to escape.

Types of Flame Retardants

Flame retardants are not all the same, and they are not interchangeable when it comes to the fire safety of materials and products. A variety of flame retardants is necessary because the elements in flame retardants react differently with fire. In addition, materials that need to be made fire-resistant are very different in their physical nature and chemical composition, and they behave differently during combustion. As a result, chemical manufacturers have developed different flame-retardant chemistries to suit different products to render them fire-resistant and allow them to retain their intended functionality and performance standards. Further innovation by the chemical manufacturing industry is being done to keep pace with advancements in technology, and, with it, a steady increase in new products.

Flame retardants are generally classified according to their chemical makeup. The most common classes of flame retardants are: Brominated, Phosphorus, Nitrogen, Chlorinated and Inorganic.

Brominated

Brominated compounds are used for a number of purposes, but the major use is as flame retardants. Bromine interacts with the fire cycle in the gas phase to stop the chemical chain reaction that leads to flame formation and a self-sustaining fire. 

Phosphorus

Flame retardants containing phosphorus interrupt the combustion process by promoting “charring.” In the presence of a heat source, phosphorus flame retardants release phosphoric acid which causes the material to char and form a thick glassy layer of carbon. This carbonated char stops the decomposition process (pyrolysis) and prevents the release of flammable gases, essentially cutting off fuel to the flame. It also provides a barrier between the material and the heat source. 

Nitrogen

Nitrogen flame retardants work in several key ways to provide fire protection. At high temperatures, they enable the formation of stable molecular compounds that stop the decomposition process (pyrolysis) and prevent the release of flammable gases.

Chlorinated

Like bromine-based flame retardants, chlorinated flame retardants interact with the fire cycle to stop flame formation.

Inorganic

A variety of inorganic compounds, most notably hydrated aluminum and magnesium oxides, are used as flame retardants, or, as is the case with antimony trioxide, as part of a flame retardant system in conjunction with bromine, phosphorus or nitrogen flame retardants.

Issues with traditional Halogenated (Brominated/Chlorinated) Flame Retardants

• Persistence

Resist breakdown in the environment (non-degradable)

• Toxicity

Firefighters at risk                    

• Dioxins and furans produced at high levels
• European Union banned the use of all polybrominated diphenyl ethers (PBDEs) and polybrominated biphenyls (PBBs) in electronic products starting in 2006.
• Halogenated Organic Compounds are considered Persistent Organic Pollutants(POP)
• Antimony Oxide – possible link to Sudden Infant Death Syndrome.
• Other effects – Elevated rates of multiple myeloma, non-Hodgkin’s lymphoma, prostate and testicular cancers

Most commonly used bromine free alternatives

• Inorganic
• Aluminium Trihydroxide

• Magnesium Hydroxide

• Ammonium Polyphosphate

• Red Phosphorous

• Zinc Borate

• Organophosphorous
• Triphenyl Phosphate

• Tricresyl Phosphate

• Resorcinol bis(diphenyl phosphate)

• Phosphonic Acid (2-((hydroxymethyl) carbamyl)ethyl)- dimethyl ester

• Phosphorous and Nitrogen containing thermosets

• Nitrogen Containing
• Melamine

Advantages of non-halogenated Exolit (from Clariant) flame retardants

• Low smoke density and smoke gas corrosivity
• Reduction of damage and extended escape times
• Highly-effective, low dosage, high polymer compatibility
• Only low impact on material properties
• Excellent incorporation into matrix
• No migration of FR
• Low fogging and VOC values
• Excellent ageing stability ppm
• Good recyclability

Exolit flame retardants offer a “green” alternative to halogenated FR for various applications.

Non-halogenated flame retardant chemicals are gaining more traction across regions due to their environment friendly nature, whereas the demand for the halogenated flame retardant chemicals are declining due to their high toxicity levels, especially in North America and Europe owing to stringent regulations.

By : Mr. P.A Murli- BE(Fire) , NESC, Nagpur