Flame retardants are materials that inhibit or resist the spread of fire. Fire is the heat and light energy released during a Chemical reaction, in particular a combustion reaction. These can be separated into several categories:
Many of these chemicals are considered harmful, having been linked to liver, thyroid, reproductive/developmental, and neurological effects.  PCBs were banned in 1977 and the EU has banned several types of brominated flame retardants as of 2008, following evidence beginning in 1998 that the chemicals were accumulating in human breast milk. Brominated flame retardants are a group of Flame retardants that consist of organic compounds containing Bromine.  Currently some US states and various countries are investigating PBDEs as well; of the major ones only decaBDE remains on the North American market. Decabromodiphenyl ether (decaBDE deca-BDE DBDE deca decabromodiphenyl oxide DBDPO bis(pentabromophenyl ether is a Brominated flame retardant which belongs to the group 
Aside from various conventional alternatives such as antinomony or phosphorus-based retardants which have toxicological problems of their own, Environmental Health Perspectives surveys the halogen-free alternatives being explored. Environmental Health Perspectives (EHP is a peer-reviewed journal of the United States' National Institute of Environmental Health Sciences, published monthly  These include a technique to fuse flame retardants into products (so no chemicals leak), nanoclays incorporating montmorillonite, an entirely new plastic which produces water when burned called bishydroxydeoxybenzoin (BHDB), and possibly other nanomaterial solutions. Montmorillonite is a very soft phyllosilicate mineral that typically forms in microscopic Crystals forming a clay. Inherently flame-resistant products are ideal, and the aerospace industry uses such plastics, but they are too costly for widespread use.
Some compounds break down endothermically when subjected to high temperatures. In Thermodynamics, the word endothermic "within-heating" describes a process or reaction that absorbs Energy in the form of Heat. Magnesium and aluminium hydroxides are an example, together with various hydrates. Hydrate is a term used in Inorganic chemistry and Organic chemistry to indicate that a substance contains Water. The reaction removes heat from the surrounding, thus cooling the material. The use of hydroxides and hydrates is limited by their relatively low decomposition temperature, which limits the maximum processing temperature of the polymers.
Inert fillers, eg. talc or calcium carbonate, act as diluents, lowering the combustible portion of the material, thus lowering the amount of heat per volume of material it can produce while burning. Talc (derived from the Persian via Arabic talq) is a Mineral composed of Hydrated Magnesium Silicate with Calcium carbonate is a Chemical compound with the Chemical formula Ca[[Carbon C]] O 3
A way to stop spreading of the flame over the material is to create a thermal insulation barrier between the burning and unburned parts. Intumescent additives are often employed; their role is to turn the polymer into a carbonized foam, which separates the flame from the material and slows the heat transfer to the unburned fuel. An intumescent is a substance which swells as a result of Heat exposure thus increasing in Volume, and decreasing in Density.
Inert gases (most often carbon dioxide and water) produced by thermal degradation of some materials act as diluents of the combustible gases, lowering their partial pressures and the partial pressure of oxygen, and slowing the reaction rate. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Water is a common Chemical substance that is essential for the survival of all known forms of Life.
Chlorinated and brominated materials undergo thermal degradation and release hydrogen chloride and hydrogen bromide. Hydrogen bromide is the diatomic molecule H[[Bromine Br]] Under standard conditions HBr is a gas but it can be liquified These react with the highly reactive H· and OH· radicals in the flame, resulting in an inactive molecule and a Cl· or Br· radical. In Chemistry, radicals (often referred to as free radicals) are atoms molecules or ions with Unpaired electrons on an otherwise Open shell The halogen radical has much lower energy than H· or OH·, and therefore has much lower potential to propagate the radical oxidation reactions of combustion. Antimony compounds tend to act in synergy with halogenated flame retardants. Antimony (IPA (Received Pronunciation, /ˈæntɪmoʊni/ (US is a Chemical element with the symbol Sb (stibium meaning "mark" and The HCl and HBr released during burning are highly corrosive, which has reliability implications for objects (especially fine electronics) subjected to the released smoke.
Flame retardants have faced renewed attention in recent years. The earliest flame retardants, polychlorinated biphenyls (PCBs) were banned in the 1977 when it was discovered that they were toxic. Polychlorinated biphenyls ( PCB s are a class of Organic compounds with 1 to 10 Chlorine atoms attached to Biphenyl which is a molecule composed  Industries shifted to using brominated flame retardants instead, but these are now receiving closer scrutinty. Brominated flame retardants are a group of Flame retardants that consist of organic compounds containing Bromine. The EU has banned several types of polybrominated diphenyl etherss (PDBEs) as of 2008, 10 years after Sweden discovered that they were accumulating in breast milk. Polybrominated diphenyl ethers or PBDE, are Organic compounds that are used as a Flame retardant.  Nearly all Americans tested have trace levels of flame retardants in their body. Recent research links some of this exposure to dust on television sets, which may have been generated from the TV heating up the flame retardants in the TV. Careless disposal of TVs and other appliances such as microwaves or old computers may greatly increase the amount of environmental contamination. 
UK scientist Barry Richardson claimed in 1989 that a fungus in bedding broke down the antimony, phosphorus, and arsenic flame retardants in infant bedding to form toxic gases. Sudden infant death syndrome (SIDS is a syndrome marked by the symptoms of sudden and unexplained death of an apparently healthy Infant aged one month to one year This research was taken up by New Zealand scientist Jim Sprott, who published a book on it, and eventually aired on The Cook Report in 1994. The Cook Report was a British Television programme shown on ITV, produced for the network by Central Television from A 1998 UK government-sponsored study called the Limerick Report found that toxic gases were not created.  Sprott maintains that his findings were not refuted.