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Fire Retardant Technologies 2014

fire retardant material

27 Jun 2014

The recent Fire Retardant Technologies 2014 international conference was held in the Darwin Lecture Theatre, University of Central Lancashire (UCLan), Preston, UK on 14 - 17 April 2014.  The delegates were welcomed by UCLan's Vice-Chancellor, Professor Gerry Kelleher who stressed the importance of ensuring that fundamental and applied research could be applied beneficially in the world.  The conference was organised by the Royal Society of Chemistry (RSC) and COST-Flaretex, with support from SCI's Fire and Materials Group.  It comprised two days of presentations on developments in fire retardant technologies followed by a workshop updating delegates on possible changes in the UK flammability regulations for upholstered furniture.  The conference was attended by over 150 delegates from some 33 countries, indicating the considerable interest in emerging fire retardant technologies.

Introduction day 1: Prof Paul Kiekens

Cost Action MP1105 on Flame Retardancy - Professor Paul Kiekens, COST-Flaretex Project Coordinator, Ghent University)
The first session was chaired by Dr Anna Stec (UCLan, UK).  Professor Paul Kiekens (COST-Flaretex Project Coordinator, Ghent University, Belgium) discussed the COST Action MP1105 on Flame Retardancy which represented on European Opportunity for cutting edge research.  The main aim was to form a European multi-disciplinary knowledge platform on sustainable flame retardancy.  This would facilitate the rapid development and commercialisation of fire-safe textiles and related materials of low toxicity/ecotoxicity, using all the available/novel technologies.  This platform would promote cooperation between researchers from different scientific disciplines to exchange ideas/strategies efficiently to lead developments in fire safety, fire retardants and environmentally-friendly fire retarded textiles/related materials.

The COST Action MP 1105 commenced in Spring 2012 and runs until 22 May 2016.  Some 27 COST countries and one non-COST country (New Zealand) have joined, the Action being organised in four working groups (WG):

  • WG1 : Novel flame retardants
  • WG2 : Toxicological / environmental aspects
  • WG3 : Processing / Applications / Commercialisation
  • WG4 : Testing / Standardisation

The spread of COST Action activities included:

  • Conferences and Workshops
  • Training schools
  • Short Term Scientific Missions
  • Initiating joint research projects

Session 1: Overview - Prof Richard Hull, Ulrike Braun

The Fire Retardant Spectrum: From Aluminium to Zinc, Red or Green? Professor Richard Hull, University of Central Lancashire)
Professor Richard Hull (Professor of Chemistry and Fire Science, University of Central Lancashire, UK) discussed the fire retardant spectrum, describing the modes of action of the many types of fire retardants available.  He pointed out that fire retardants can act chemically and/or physically in the solid, liquid or gas phase, and demonstrated how specific polymer – fire retardant systems may have more than one mode of action.  The elucidation of the fire retardant mechanisms was aggravated by the effect of the fire retardant on the structure of the polymer.

The gas phase action of halogens and phosphorus was described as well as the action of diluents such as metal hydroxide and metal carbonates.  Cross-linked polymers produce less volatiles and more char provided the cross-links were thermally stable.  Char formation could involve cross-linking, aromatisation, fusion of aromatics, turbostratic char formation and graphitisation.  Intumescent systems, on heating, gave a swollen multicellular char which was more capable of protecting the underlying material from the action of the flame.  Polymer nanocomposites functioned through barrier layer formation, changing the thermal response, and through chemical effects such as catalysing char formation, changing the composition of the volatiles and releasing fire retardant agents.

Professor Hull concluded that fire was difficult to understand and different fire retardants were needed for different polymers.  There were plenty of alternatives to halogenated fire retardants but the hard work was to get the formulation to meet all the product demands.

Techniques for Understanding Fire Retardant Behaviour – Ulrike Braun, BAM Federal Institute of Materials Research and Testing, Berlin)
Ulrike Braun (BAM Federal Institute for Materials Research and Testing, Berlin, Germany) discussed techniques for understanding fire retardant behaviour.  Fire tests depended upon the application of the material and included flammability tests and the cone colorimeter test.  Thermal decomposition methods could utilise thermogravimetric analysis (TGA) coupled with evolved gas analysis (EVA) using FTIR (Fourier Transform Infra Red) spectroscopy.  The fire behaviour could be understood by molecular decomposition models and both thermo- and thermo-oxidative decomposition need to be considered.  The limitations of TGA-EVA were:

identification of decomposition products required high user knowledge;
no useful air measurements due to major total oxidation in the transfer system; and
no separation of chemically similar decomposition products due to overlapping spectra/fragmentation pattern.

The requirements for an improved method were:

controlled decomposition process;
chromatographic system is necessary; and
easy cleaning.

A new method had been developed based upon thermogravimetric solid-phase extraction using thermal desorption gas chromatographic mass spectrometry (TGA-SPE/TDS-GC-MS).  Using this new method the results of tests upon nylon 6.6 had shown synergistic effects to TGA-EGA, coupled with improved understanding of decomposition models.

Session 1: Overview - Prof Baljinder Kandola, Dr Sergei Levchik

Fire Retardant Behaviour Composites  -  Professor Baljinder Kandola, University of Bolton
Professor Baljinder Kandola (University of Bolton, UK) discussed the fire retardant behaviour of fibre-reinforced polymeric composites.  The flammability of thermoset resins decreased in the series vinyl ester and unsaturated polyester (highest) > epoxy > Bismaleimide > Polyimide > Phenolic (lowest).  The various approaches described involved developing flame retardant resins.  High loadings of fire retardant additives could reduce the mechanical properties of laminates.  A possible solution was to use reactive flame retardants or intumescents with/without nanocomposites.  The structural integrity of composite laminates during and after exposure to fire was important.  Chemical, polymerisable coatings can have effective flame retardant and thermal barrier properties.  The use of nanoparticles in reinforced chemical coatings was the way forward.

Gas Phase Flame Retardants - Dr Sergei Levchik, ICL-IP, USA
Dr Sergei Levchik (ICL-IP, USA) in describing how the action of gas phase flame retardants could be elucidated concluded that halogenated flame retardants remained the most efficient gas phase-active flame retardants.  Halogenated flame retardants easily split off active species which are not involved in secondary reactions.  Antimony trioxide mostly helped with the transport of halogens into the gas phase, but it also participated in the flame inhibition.  Halogenated flame retardants also showed significant condensed phase and physical effects.

Dr Levchik pointed out that phosphorus-based flame retardants should split out a volatile fragment or evaporated, but phosphorus was more prone to the secondary reactions in the condensed phase.  Volatilisation of phosphorus as an organic molecule or fragment led to heat generation as the organic part burned off in the flame.  Thus small organic groups were better.  Phosphorus was a more efficient flame inhibitor than halogens but a lower concentration of phosphorus was achieved in the flame, limiting the effectiveness in flame inhibition.

Session 2: Flame Retardant Strategies - Professor José-Marie Lopez-Cuesta, Professor John Ebdon, Professor Giovanni Camino

Fire Retardancy of Novel Hydrated Alumina in EVA - Professor Jose-Marie Lopez-Cuesta, Ecole des Mines d'Ales, France
In the second session, chaired by Professor Baljinder Kandola (University of Bolton, UK), Professor Jose;-Marie Lopez-Cuesta (Ecole des Mines d'Ales, France) discussed the flame retardancy of ethylene vinyl acetate (EVA) using new aluminium-based fillers, namely five types of hydrated alumina.  A variety of analytical techniques were used such as TGA and DTG, cone calorimeter data and the pyrolysis combustion flow calorimeter (PCFC).  The results showed that pseudoboehmites [AlO(OH) 0.66H2O and AlO(OH) 0.60H2O] exhibited greater flame retardant properties compared with commercial aluminium trihydroxide [Al(OH)3] and boehmite [AlO(OH)] by promoting a significant reduction in peak heat release rate (PHRR) values.

The improvement in fire performance was not explained by an increase in the melt viscosity, or the role of the endothermic effect and an increase of EVA thermal stability.  It was demonstrated through the use of PCFC in combination with the cone calorimeter data that the predominant factor is the barrier effect.  Environmental stereoscanning electron microscopy coupled with elemental analysis using EDX showed that the barrier effect in the case of pseudoboehmites was mainly caused by an outstanding migration phenomenon which generated a rapid formation of a cohesive and homogeneous insulating layer.

Phosphorus Compounds as Condensed Phase Flame Retardants for Polymer-based Materials, Professor John Ebdon, University of Bolton
Professor John Ebdon (University of Bolton, UK) discussed the use of phosphorus compounds as condensed phase flame retardants for polymer-based materials, concentrating on the modes of action of:

  • Inorganic phosphorus compounds;
  • Organophosphorus compounds;
  •  Reactives
  •  Additives
  • Elemental phosphorus; and
  • Mixed element flame retardants.

Session 2: Flame Retardant Strategies - Professor Giovanni Camino, Professor Yuan Hu, Dr Jenny Alongi

Novel Nanocomposite Fire Retardants, Professor Giovanni Camino, Politecnico di Torino, Italy
Novel nano-composite fire retardants were reviewed by Professor Giovanni Camino (Politecnico di Torino, Italy).  The action of three-dimensional (3D) particles e.g. silica, 2D tubes e.g. carbon nanotubes, sepiolates, and 1D lamellar inorganics such as phyllosilicates, phosphates etc. on flame retardancy were discussed.  Low melting synthetic hybrid talc provided lamellar interspace engineering, and hollow spherical nanoball allophones were also an interesting development.  Layered double hydroxide-montmorillonite could lead to combined flame retardant mechanisms possibly leading to synergistic improvements in effectiveness.  The use of nanocellulose nanofiller and graphite-derived nanoparticles such as graphene nanoplatelets, and graphite nanocomposites were also new developments.  Flame retardants could also be generated in situ via the sol-gel approach by reactive extrusion.

Synthesis and Mechanism of Flame Retardant Microencapusulation and Inorganics Additives , Professor Yuan Hu, University of Science & Technology of China, China

Professor Yuan Hu (University of Science & Technology of China (UTC), China) described the preparation of silica gel microencapsulated ammonium polyphosphate (APP) and its migration mechanism.  Micro-encapsulation could be used to:

  • protect sensitive substances;
  • mask the organoleptic properties;
  • obtain controlled release;
  • provide safe handling; and
  • avoid adverse effects.

Using sol-gel microencapsulation the APP core was enclosed within a silica gel shell.  The crosslinked shell material improved the water resistance, imparted better compatibility within thermoplastic polyurethane, provided a higher initial degradation temperature, while silicon was an excellent flame retardant.  Together all these compounds provided a nitrogen-phosphorus synergistic flame retardant.

The production of a vinyl group-functionalised silica microcapsule decreased the water solubility and changed the surface properties of the flame retardant from hydrophilic to hydrophobic.  The presence of silica in the shell of the microencapsulated flame retardant improved the char stability, especially at higher temperatures thereby protecting EVA from decomposing during a fire.  An increase in tensile strength and decrease in elongation at break of the flame retarded EVA occurred because of irradiation induced crosslinking while the hydrophobic silica gel shell could be considered as an insulating shield which could isolate the flame retardant from the EVA matrix.  The migration mechanism of the silica microcapsule was also studied using ATR-FTIR and XPS analysis of the carbon layer.

Layer by Layer Assembly: A Current Emerging Technique for Conferring Flame Retardancy, Dr Jenny Alongi, Politecnico di Torino, Italy
Dr Jenny Alongi (Politecnico di Torino, Italy) gave a presentation on layer by layer assembly : a current emerging technique for conferring flame retardancy co-authored by her colleagues Federico Carosio and Giulio Malucelli.  Nanocoatings could be generated by:

  • nanoparticle adsorption;
  • layer by layer assembly;
  • sol-gel processes;
  • dual-cure processes;
  • biomacromolecule-based coatings; and
  • enzyme immobilisation.

Layer by layer assembly nanocoatings are based upon the attraction of oppositely charged species using water as a solvent.  All polyelectrolyte species can be used at very low concentrations (<1wt%), the deposition occurring regardless of the substrate type and shape.  Multifunctionality is possible with no changes in colour or mechanical properties of the substrate.  Silica and zirconium phosphate-based treatments yield barrier effects on polyester via inorganic coating.  Ammonium polyphosphate-based treatments yield an organic-inorganic coating that provides a barrier effect on polyester/cotton plus the release of phosphorus-based flame retardants.

Char-forming coatings based upon chitosan plus ammonium polyphosphate and the quadlayer based upon PDAC/PAA/PDAC/APP were described where PDAC [poly (diallyldimethyl ammonium) chloride], PAA (polyacrylic acid), PDAC, and APP (ammonium polyphosphate) are sequentially deposited on the fibre surface.  Biomacromolecules could offer a new era for flame retardant materials using deoxyribose nucleic acid (DNA) which could be considered as an all-in-one intumescent material (negatively charged) applied with chitosan (positively charged) to form multiple bilayer coatings.  Dipping or spraying could be used to form layer by layer assembly.

Session 3: Applications of Fire Retardants - Dr John Liggat, Dr Andrew P Taylor, Dr Sabyasachi Gaan

Intumescence: A Versatile Concept for Diverse Applications, Dr John Liggat, University of Strathclyde
In the third session, chaired by Dr John Liggat (University of Strathclyde, UK), Professor Serge Bourbigot (&Eacute;cole Nationale Sup&eacute;rieure de Chimie de Lille (ENSCL), France) gave a detailed overview of intumescence, a versatile concept for diverse applications.  Carbon fibre reinforced plastics in aircraft structures has introduced potential fire threats.  Silicone-based highly intumescent coatings based upon a silicone matrix (56%) expandable graphite (25%), calcium carbonate (12%) and clay (7%) gave good fire protection through the heat barrier produced by high expansion under the action of heat.  The protective barrier possessed high structural cohesion because of chemical interactions (SiC, Ca-Si).

Small scale furnace tests had shown that intumescent paints could decrease the temperature rise in steel, and inorganic formulations which were halogen-, phosphorus- and boron-free could decrease smoke opacity.  The residual intumescent layer could also give thermal protection against initial blasting by a hot airjet at 900&deg;C.  Studies on polylactic acid (PLA) using a PLA racemic crystal structure (SC-PLA) had shown it to consist of alternating L- and D-PLA chains packed side by side with a 1:1 ratio of L:D monomer units.  Production of the PLA stereocomplex by reactive extrusion and incorporation of melamine-ammonium polyphosphate and C30B had decreased the total heat release by 75% and the peak heat release by 70%.

Developments in Fire Resisting Intumescent Coatings for Structural Steel - Dr Andrew P Taylor, Sherwin Williams, Bolton

In the third session on applications of fire retardants Dr Andrew P Taylor (Sherwin-Williams, Bolton, UK) discussed developments in fire resisting intumescent coatings for structural steel in an offshore environment.  The differences between civil construction and offshore environments depended upon:

  • cellulosic curve versus hydrocarbon curve;
  • offshore steel failure temperature 400C versus civil construction 500C
  • life barrier versus structure protection; and
  • different fire cases  - jetfire and explosion risk.

Thin film (300 micrometres to 2mm) intumescent coatings dealt with cellulosic fibres, the resin binder usually melting in the fire, the volume expansion being up to 50 times.  Thick film (3mm to 20mm) intumescent coatings dealt with both hydrocarbon and cellulosic fibres, the resin binder epoxy not melting but being very durable to give a low volume expansion of up to five times.  Different fire cases had be considered:

  • jetfires;
  • point fire with lots of fuel;
  • extreme turbulence;
  • divisions - life barrier; and
  • explosion testing.

The considerations surrounding appropriate test procedures were discussed and then BLEVE (boiling liquid expanding vapour explosions) were described using a test on an unprotected propane gas (LPG) vessel.

Reinforcement of coatings at mid-depth using metal mesh or high temperature fibre cloth could be used with mesh-free coatings a possibility for the future.  Many products used boric acid / borate chemistry which gave good results but borates had toxicological/environmental hazards.  New chemistry was directed towards finding a material that releases water early in a fire and had vitrifying properties to replace the use of borates.

Offshore fire protection had used intumescent technology successfully for over 20 years but it was a challenging market to be in due to:

  • severe fire protection requirements;
  • challenging environment/lifetime performance guarantees; and
  • safety critical coating systems.

Recent Developments in N and P Based Flame Retardants - Dr Sabyasachi Gaan, Empa, St Gallen, Switzerland
Dr Sabyasachi Gaan (Empa, St Gallen, Switzerland) discussed recent developments in nitrogen and phosphorus-based flame retardants.  Research studies had demonstrated that phosphoramidates had a strong condensed (i.e. solid) phase activity on cellulose (e.g. cotton and viscose), the functional group of the amine playing an important role.  The smaller methyl group ester had a higher flame retardant efficacy compared with the ethyl group ester.  Aromatic bis-phosphoramidates were stable to hydrolysis and suitable for viscose fibre yielding a lower heat release and higher char content.

On polyurethane foams the standard commercial flame retardants were Exolit OP560 and Tris (2 chloroisopropyl) phosphate (TCPP).  Phosphoramidates and phosphonates were better than phosphates for flame retarding polyurethane foam, the former primarily exhibiting gas phase activity.  Phosphonamidates were versatile flame retardants with bis- and multi-DOPO derivatives (DOPO = 9,10-dihydro-9-oxa-phosphaphenanthrene-10-oxide) providing the best flame retardant rating on polyurethane foam.  Various DOPO derivatives were shown to be gas-phase-active flame retardants for thermoplastic polymers such as polyamide 6 fibres.  Hybrid flame retardants had been developed at Empa based upon a meltable Phosphorus-based additive with high thermal stability and built-in condensed and gas phase activity.  Hybrid flame retardants could be applied to various polyester production methods for polyethylene terephthalate and polybutylene terephthalate fibres.

Session 3: Applications of Fire Retardants -Dr Roland Kramer, Franck Gyppaz,

Industrial Applications of Flame Retardants for Thermoplastics - Dr Roland Kramer, BASF SE, Ludwigshafen, Germany
Dr Roland Kramer (standing in for Dr Martin Klatt) (BASF SE, Ludwigshafen, Germany) then discussed industrial applications of flame retardants for thermoplastics.  A flame retardant must prevent ignition / flame spread under defined risk scenarios and must prove its action under defined and standardised test conditions e.g. the UK 94 test and glow wire test.  Considerations other than flame retardancy were also important such as:

  • toxicological / operational safety;
  • price;
  • processing (mould deposits, corrosion);
  • electrical properties;
  • migration during use;
  • mechanical properties; and
  • other properties e.g. colour, odour etc.

Issues such as corrosion and wear affected the choice of materials for compounding machinery and migration of the flame retardant during end use application could create problems.  Off-gassing of flame retardant during injection moulding could also give rise to problems.  Halogenated flame retardants used on thermoplastics included polypentabromoacrylate, polybromostyrene and TBBA-polycarbonate.  Oligomeric flame retardants were non-migrating.  Ultradur B4300G6 and Ultradur B4406G6 were flame retardants for use on polybutylene terephthalate (PBT).

Red phosphorus-based Ultramid A3WG5 and Ultramid A3X2G5 gave high performance at low loading in polyamide 66 and other BASF additives in the Ultramid range gave best in class impact properties and excellent mechanical properties in polyamide and high temperature polyamide.  Melapur MC based on melamine cyanurate, phosphinic acid and melamine salts were also used in PBT, polyamide 66 and high temperature polyamide.  The latter provided both gas phase inhibition and charring.

Fire Retardant Cables - Franck Gyppaz, Nexans Research Centre, Lyon France
Fire safety in buildings &ndash; reaction to fire and cable applications was discussed by Franck Gyppaz (Nexans Research Centre, Lyon, France). Nexans had produced a novel self-ceramifying technology (INFIT Technology) for new fire resistant cables.  Cables are also used as conductors, insulation, bedding and sheath and can be anywhere in a building.  They were not generally the source of fire but, being composed of combustible organic material to various degrees, could be a vital vector for fire propagation and gas emission.

Standard cables used PVC (polyvinyl chloride) material as the jacket and/or insulation.  The system was cost-effective and usually comprised PVC, plasticiser, filler, stabiliser and additives.  However these produced opaque smokes and 90% of deaths, during fire, result from smoke inhalation.  The gases in smoke could be irritants and impact on the evacuation time.

Cables with high fire retardancy were mainly based upon LSZH (low smoke zero hazard) material which gave, in cone calorimeter tests, low peak HRR, THRR and low smoke production.  Fillers were key components of LSZH materials.  Fillers were available to delay ignition, reduce peak HRR, decrease smoke production and increase char cohesion.  In this way a range of cable materials had been devised that could produce either flame retardant properties or fire retardant properties, the latter being more costly to produce.

Session 4: Testing, Toxicity and the Environment - Professor Richard Hull, Dr Anna Stec, Professor Heather M Stapleton

Fire Safety Regulations and Testing - Their Impact on the Use of Polymers and Flame Retardants &ndash; Professor Richard Hull, University of Central Lancashire
In the fourth session, chaired by Professor Richard Hull (University of Central Lancashire, UK), Dr Jurgen H Troitzsch (Fire & Environment Protection Service, Hessen, Germany) then discussed the latest developments in fire safety regulations and testing and their impact on the use of polymers and flame retardants.  Fire protection regulations in most countries cover building and construction, transportation (all forms), electrical and electronic equipment, furniture and furnishings and textiles.  A summary of Dr Troitzsch's very detailed paper follows.

For buildings in the European Union, EU reaction to fire classification and tests cover:

  • small ignition sources : flammability to EN ISO 11925-2 and;
  • larger ignition sources: time to ignition, heat release, lateral flame spread to EN13823;
  • Classification and tests compulsory for all EU Member States, fire safety levels still national;
  • New Construction Products Regulation (CPR) requires revision of all EU product standards for obtaining CE-Mark;
  • Focus on dangerous substances (contents, emissions) in EU product standards; and
  • Possible barriers to trade against CE-Mark from national indoor emission marks (Germany, France, Belgium).

Summary of Fire Safety of Rail Vehicles in the EU:

  • EN 45545-2 reaction to fire classification and tests cover
  • Smaller ignition sources : radiant panel tests at 25kW/m2 and in some cases flammability to EN ISO 11925-2 and Oxygen index to EN ISO 4589-2
  • Larger ignition sources : radiant panel tests at 50kW/m2
  • Revision of EN 45545-2 with proposals for
  • Continuous smoke gas toxicity measurement
  • Fire tests for seats with higher burner performance (28kW)
  • Lower heat fluxes in cone and smoke chambers (35 kW/m2)
  • Most EU railways fire tests also internationally used for ships in the IMO Fire Test Procedures (FTP) Code

Summary of Fire Safety in E&E

  • E&E ignition/flammability classification and tests cover
  • Smaller ignition sources: open flame and glow wire tests for materials and end products simulating malfunction of electrical parts
  • Introduction of requirements for external ignition sources
  • Failed because of campaigns against flame retardants
  • Flame retardants are necessary for meeting ignitability/flammability requirements in E&E equipment
  • Not using flame retardants in E&E equipment may dramatically increase the number of fires caused by malfunction of electrical parts and external ignition sources

Summary of Fire Safety Furniture and Furnishings

  • Fire tests for furniture in private homes
  • Smaller ignition sources : smouldering (cigarette) and open flames (small burners)
  • Larger ignition sources : Bunsen burners, wood cribs
  • Revised California TB 117 now only with cigarette test because here no FRs are needed. Result of campaigns against FRs
  • The elimination of open flame tests reduces fire safety of furniture and time for escape

Fire Retardants and Smoke Toxicity &ndash; Dr Anna Stec, University of Central Lancashire
Dr Anna A Stec (University of Central Lancashire, Preston, UK) discussed fire retardants and fire smoke toxicity pointing out that increasingly synthetic polymer materials were being used as substitutes for natural-based materials.  Recent research focussed on preventing ignition and fire growth, shifting the focus of fire safety towards reducing peak heat release rates (PHRRs).  Fire safety relied upon valid modelling of appropriate fire scenarios and different existing bench-scale test methods were adapted for the hazard assessment.  Fire hazards included impaired vision from smoke obscuration, pain and breathing difficulties from smoke irritants, asphyxiation from toxic gases, and pain to exposed skin and respiratory tract followed by burns from exposure to radiant/convected heat leading to collapse.

In a wide-ranging presentation Dr Stec concluded that:

  • Fire retardants which act in the gas phase ('flame retardants') often increase fire effluent toxicity;
  • CO is a good indicator of incomplete combustion however it is not always the major toxicant. The asphyxiants, CO and HCN, are much more prevalent in developed flaming;
  • Brominated flame retardants increase the yield of both CO and HCN, and have a more pronounced effect than aluminium phosphinate;
  • Insulation materials vary widely in their toxic product yields, and potential hazard; and
  • Irritants (e.g. organics and smoke particles) are also more prevalent in developed flaming, while HCI is independent of fire condition and Nox is favoured by well-ventilated conditions.

Environmental Concerns Regarding Chemical Flame Retardants &ndash; Professor Heather M Stapleton, Duke University, North Carolina, USA
In a challenging presentation Associate Professor Heather M Stapleton (Duke University, Durham, North Carolina, USA) described current environmental concerns regarding chemical flame retardants, focussing principally upon brominated flame retardants (BFRs) and organophosphate flame retardants (OPFRs):

  • polybrominated diphenyl ethers (PBDEs);
  • hexabromocyclododecane (HBCD);
  • tetrabromobisphenol A (TBBPA);
  • tris (1,3-dichloropropyl phosphate) (TDCPP); and
  • triphenyl phosphate (TPP).

She pointed out that additive flame retardants migrate out of products over time and contaminate indoor air and dust particles.  Flame retardant chemicals can persist for:

> 2 months in water;
> 6 months in sediment/soil; and
> probably 6 months in indoor dust.

The Bioaccumulation Potential may be increased because the halogenation (bromination/chlorination) increases the hydrophobicity of the flame retardant molecule, increasing log KOW.  There was now widespread PBDE contamination of water, sediments, biosolids and biota (i.e. the flora and fauna of a region).  Bioaccumulation in aquatic and terrestrial food webs has occurred with the dominant congeners BDE-47, BDE-99, BDE-100, BDE-153 and BDE 154.  The bioaccumulation in fish was ten times higher in North America than in Europe.  BDE-209 (Decabromodiphenyl ether) and higher congeners were increasing in Herring Gull eggs (Great Lakes) with a doubling time of around 2-5 years.  In human samples the PBDE levels (ng/g lipid) were in the order North America > Europe > Japan.

Children's exposures to PBDEs were greater than in adults because children were spending more time indoors, and indoor environments are often more polluted than outdoor environments (PBDEs in dust >>>>> PBDEs in soils).  In addition children have a high number of hand-to-mouth contacts and are physically in contact with many flame retardant treated products.  Handwipe tests showed that the PBDE residues on the hands could reasonably predict the level of PBDEs in the body.  Prenatal PBDE levels measured in 301 women at 16 weeks gestation showed that with each 10-fold increase in serum PBDEs there was a five point decrement in Bayky's Mental Development Index, and a 7.5 point decrement in Weschler's Full Scale Test of IQ (Intelligence Quotient).  Increased hyperactivity symptoms were also observed with increased exposure levels.

PentaBDE had been phased out and replaced by TDCPP, TCPP and Firemaster 550 (Chemtex).  DecaBDE was being replaced with Decabromodiphenyl ethane.  TDCPP and its brominated analogue had been shown to be mutagenic, with increased incidence by tumours in rats exposed to TDCPP over two years.  Heather Stapleton said that her studies also suggested TDCPP may also be a neurotoxicant.  The primary metabolite of TDCPP had been detected in >95% of human urine samples in the USA.  TBBPA had been found to affect thyroid hormone regulation and experimental studies on rats suggested that it could possibly be a potential carcinogen.

New flame retardants detected in the environment included TBC (Tris (2,3-dibromopropyl) isocyanurate (used in polypropylene, polyethylene and polystyrene), and also OBIND (octabromotrimethylphenylindane), detected in birds eggs.  The latter was used in several types of plastics.  The human health effects of these flame retardants were currently unknown.

Heather Stapleton completed her fact-filled presentation with a challenging question, namely, 'Are there better ways to maintain fire safety without the use of additive flame retardants?'  At present, the answer is no, but if the environmental concerns over the use of additive flame retardants continue to spiral, other approaches to flame retarding fibres, polymers and plastics will have to be discovered.

Ian Holme

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