Hazardous Chemicals Handbook 2 Episode 6 pot

218 FLAMMABLE CHEMICALS Table 6.9 Pyrophoric chemicals in common use Pyrophoric alkyl metals Carbonylpotassium Pyrophoric metal Triethylarsine and derivatives Carbonylsodium sulphides Triethylborane Groups Dodecacarbonyldivanadium (Ammonium sulphide) Triethylphosphine Alkyl lithiums Dodecacarbonyltetracobalt Barium sulphide Triisopropylphosphine Dialkylzincs Dodecacarbonyltriiron Calcium sulphide Trimethylarsine Diplumbanes Hexacarbonylchromium Chromium (II) sulphide Trimethylborane Trialkylaluminiums Hexacarbonylmolybdenum Copper (II) sulphide Trimethylphosphine Trialkylbismuths Hexacarbonyltungsten Diantimony trisulphide Nonacarbonyldiiron Dibismuth trisulphide Pyrophoric alkyl Compounds Octacarbonyldicobalt Dicaesium selenide non-metal halides Bis-dimethylstibinyl oxide Pentacarbonyliron Dicerium trisulphide Butyldichloroborane Bis(dimethylthallium) acetylide Tetracarbonylnickel Digold trisulphide Dichlorodiethylsilane Butyllithium Europium (II) sulphide Dichlorodimethylsilane Diethylberyllium Pyrophoric metals Germanium (II) sulphide Dichlor(ethyl)silane Diethylcadmium (in finely-divided state) Iron disulphide Dichloro(methyl)silane Diethylmagnesium Caesium Iron (II) sulphide lododimethylarsine Diethylzinc Calcium Manganese (II) sulphide Trichloro(ethyl)silane Diisopropylberyllium Cerium Mercury (II) sulphide Trichloro(methyl)silane Dimethylberyllium Chromium Molybdenum (IV) Trichloro(vinyl)silane Dimethylbismuth chloride Cobalt sulphide Dimethylcadmium Hafnium Potassium sulphide Pyrophoric alkyl Dimethylmagnesium Iridium Rhenium (VII) sulphide non-metals Dimethylmercury Iron Silver sulphide Hydrides Dimethyl-phenylethynylthallium Lead Sodium disulphide Diethylarsine Dimethyl-l-propynlthallium Lithium Sodium polysulphide Diethylphosphine Dimethylzinc Manganese Sodium sulphide Dimethylarsine Ethoxydiethylaluminium Nickel Tin (II) sulphide 1,1-Dimethyldiborane Methylbismuth oxide Palladium Tin (IV) sulphide 1,2-Dimethyldiborane Methylcopper Platinum Titanium (IV) sulphide Dimethylphosphine Methyllithium Plutonium Uranium (IV) sulphide Ethylphosphine Methylpotassium Potassium Methylphosphine Methylsilver Rubidium Pyrophoric alkyl Methylsilane Methylsodium Sodium non-metals Poly(methylenemagnesium) Tantalum Bis(dibutylborino) Propylcopper Thorium acetylene Tetramethyldistibine Titanium Bis-dimethylarsinyl oxide Tetramethyllead Uranium Bis-dimethylarsinyl Tetramethylplatinum Zirconium sulphide Tetramethyltin Bis-trimethylsilyl oxide Tetravinyllead Alloys Dibutyl-3-methyl-3- Triethylantimony Aluminium–mercury buten-1-ynlborane Triethylbismuth Bismuth–plutonium Diethoxydimethylsilane Triethylgallium Copper–zirconium Diethylmethylphosphine Trimethylantimony Nickel–titanium Ethyldimethylphosphine Trimethylgallium Tetraethyldiarsine Trimethylthalium Pyrophoric non-metals Tetramethyldiarsine Trivinylbismuth and metal carbides Tetramethylsilane Vinyllithium Phosphorus Tribenzylarsine Silane mixo-Tributylborane Pyrophoric carbonyl metals Phosphine Tributylphosphine Carbonylithium Calcium carbide Uranium carbide Rarely found uncombined Other types of explosion involve, • Pressure rupture, due to rapid release of high pressure. Blast is generated by rapid expansion of gas down to atmospheric pressure and rupture of the container generates missiles. • Steam explosion: rapid vaporization of water within molten metal, molten salts or hot oil or through them contacting surface or adsorbed moisture (refer to page 47). The last two types do not involve a combustion reaction but the damage they cause can similarly be related to the overpressure generated at a given distance from the event. Control measures Strategies for handling flammable materials • Minimize at the design stage the risk of fire/explosion, e.g. by substitution with a less volatile chemical or operation at lower temperature, avoidance of air ingress or use of inerting. Design to minimize leakages and avoidance of potential ignition sources. Table 6.10 Electrochemical series Metal Symbol Electro-negativity Occurrence Reactivity with water Lithium Li 0.97 Caesium Cs 0.86 React with cold water to Potassium K 0.91 Never found yield hydrogen Barium Ba 0.97 uncombined Strontium Sr 0.99 Calcium Ca 1.04 Sodium Na 1.01 Magnesium Mg 1.23 Aluminium Al 1.47 Burning metals decompose Manganese Mn 1.60 water and hot metals Zinc Zn 1.66 decompose steam Chromium Cr 1.56 Iron Fe 1.64 Cadmium Cd 1.46 Cobalt Co 1.70 Nickel Ni 1.75 Very little reaction unless Tin Sn 1.72 at white heat Lead Pb 1.55 Hydrogen H 2.20 Phosphorus P 2.06 Oxygen O 3.50 Bismuth Bi 1.67 Copper Cu 1.75 Sometimes found Mercury Hg 1.44 uncombined Silver Ag 1.42 Inactive with water or steam Platinum Pt 1.44 Found uncombined Gold Au 1.42 with other elements CONTROL MEASURES 219 220 FLAMMABLE CHEMICALS • Minimize the risk by appropriate systems of work. • Mitigate the effects of fire or explosion, e.g. by detection provision, spacing, appropriate construction materials, shielding, venting, extinguishment, provision for evacuation of personnel. Fire prevention Theoretically, if one corner of the ‘fire triangle’ is eliminated a fire or explosion is impossible. However, in practice, if flammable gases or vapours are mixed with air in flammable concentrations, sooner or later the mixture is likely to catch fire or explode because of the difficulty of eliminating every source of ignition. For reliable control of flammable materials, including combustible dusts, the aim is to remove two corners from the fire triangle. This can include some combination of: • Prevention of a mixture forming within the flammable range. • Elimination of ignition sources (see Table 6.3). Fire control Fire detection and suppression form the basis of fire control, with emergency back-up procedures to mitigate the consequences. Selected key tactics for working with flammable chemicals are summarized in Table 6.11. Refer also to ‘Fire extinguishment’ (page 221). Dust explosions The avoidance, and mitigation of the effects, of a dust explosion may involve some combination of: • Elimination of ignition sources, which is inherently difficult to ensure. • Atmosphere control, e.g. controlling dust concentrations or inerting. • Containment of explosion overpressure, i.e. by designing plant capable of withstanding in excess of the maximum explosion overpressure, or safe venting of forces, e.g. via blow-off panels, doors, membranes. • Limitation of inventory. • Restriction of spread by means of baffles, chokes or by advance inerting. • Use of water sprays or very rapid injection of suppressant gas or powder. • Good housekeeping, particularly to avoid a devastating secondary explosion, following redispersion of any accumulations of combustible dust. A similar logic is applicable to the control of explosions involving gas or vapour, but other measures, e.g. dispersion by steam or containment by water curtains, may be applicable to vapour clouds in the open air. Containment or diversion of a blast (e.g. by blast walls) and reducing its effect by appropriate spacing of equipment, buildings etc. are also applicable. Pyrophorics Control measures to reduce the risk from handling pyrophorics include: • Handling and storing the minimum quantities necessary at any time. • Segregation of the material from other chemicals, particularly‘fuels’, i.e. solvents, paper, cloth etc. • Handling in dry, chemically-inert atmospheres or beneath other appropriate media, e.g. dry oil or inert gas. • Handling in solution (e.g. aluminium alkyls in petroleum solvents). • Immediate destruction and removal of spilled materials. • Careful selection and provision of appropriate fire extinguishers in advance. • Provision and use of appropriate eye/face protection, overalls and gloves. Fire extinguishment Detection If a flammable gas or vapour is present, a pre-fire condition may be identified by a flammable- gas detector. This will actuate an alarm at a fraction of the LFL. Banks of detectors may be installed at high or low level depending, in part, upon the gas density. Fire detection may be by: Table 6.11 Control measures for working with flammable chemicals Substitute with less volatile/flammable material where possible (i.e. higher flash point/autoignition temperature, lower vapour pressure) Check on legal requirements and relevant standards/codes etc. Minimize quantities in use/in store Keep below LEL, e.g. chill to lower airborne concentration, use exhaust ventilation, inerting, keep air out. Design plant/equipment so as to contain the material and provide adequate dilution or exhaust ventilation as appropriate Provide means to contain spillages, e.g. bund walls, kerbs Eliminate ignition sources Eliminate static Consider need for inerting, flame arresters, pressure relief valves, explosion vents (venting to safe location) Consider need for checks on oxygen levels or loss of inert medium Apply appropriate zoning criteria, e.g. with respect to standards of electrical equipment (refer to Table 12.6) Set up procedures to prevent inadvertent introduction of other ignition sources and to avoid oxygen enrichment: Physical segregation, e.g. fences Warning signs to indicate flammable hazard, no smoking etc. Permits–to-work (including hot work permits) Safe systems of work to control plant modifications etc Keep flammable chemicals apart from oxidizing agents Design layout to avoid domino effects/fire spread Segregate ‘empty’ and ‘full’ containers Check for plant integrity/flammable leaks periodically or continuously on-line, as appropriate Install appropriate fire/smoke detection, audible alarms Provide adequate fire suppression systems Deal with mishaps such as spillage immediately Train staff in hazards and precautions, and practise emergency evacuation drills Remember that flammable chemicals can also be toxic or asphyxiant FIRE EXTINGUISHMENT 221 222 FLAMMABLE CHEMICALS • Personnel, e.g. operating, maintenance or security staff, or neighbours, or passers-by. • Heat sensing, as actual temperature or rate-of-temperature rise, and depending upon melting of a metal (fusion); expansion of a solid, liquid or gas; electrical sensing. • Smoke detection depending upon absorption of ionizing radiation by smoke particles; light scattering by smoke particles; light obscuration. • Flame detection by ultraviolet radiation or infra-red radiation sensing. A combination of detectors may be appropriate. They may activate an alarm only, or actuate a combined alarm/extinguishment system. With a bank of detectors a voting system may be used to increase reliability and reduce the frequency of spurious alarms. Detection/alarm systems may also be interlinked with, e.g., fire-check doors held back on electromagnetic catches such that the doors close automatically upon activation of the detection system. Extinguishment Removal of one of the corners of the fire triangle normally results in extinguishment of a fire. Propagation of a flame can also be stopped by inhibition of the chain reactions, e.g. using dry powders or organo–halogen vaporizing liquids. Classification of fires Class Type A Fire involving solid materials, generally organic materials, in which combustion normally takes place with the formation of glowing embers. B Fire involving a liquid or liquefiable solid (the miscibility or otherwise with water is an important characteristic). C Fire involving a gas. D Fire involving a burning metal, e.g. magnesium, aluminium, sodium, calcium or zirconium. An additional class not currently included in British Standard EN2 is Class F fires including cooking oils or fats. Electrical fires are not classified since any fire involving, or initiated by, electrical equipment will fall within Class A, B or C. Fire-extinguishing materials The penetration and cooling action of water is required with Class A fires, e.g. those involving paper, wood, textiles, refuse. Water is applied in the form of a jet or spray; foam or multi-purpose powder extinguishers are alternatives. Extinguishment of a Class B fire can be achieved by the smothering action of dry chemical, carbon dioxide or foam. Most flammable liquids will float on water (refer to Table 6.1 under ‘Specific gravity’), so that water as a jet is unsuitable: a mist may, however, be effective. Water is also widely used to protect equipment exposed to heat. Dry powders are effective on flammable liquid or electrical fires. Foam is a proportioned mixture of water and foam concentrate aspirated with air to cause expansion, e.g. from 6 to 10 times the volume (low expansion foam) up to >100 times (high expansion foam). It transports water to the surface of flammable liquids and enables it to float and extinguish the fire. An effective system depends upon: • The type of flammable liquid – determines the type of foam, e.g. standard or alcohol-resistant grade. Aqueous film-forming foam may be used for rapid ‘knock-down’. • The type of hazard – determines the method and rate of application, e.g. by fixed pourers, mobile monitors, portable foam-towers or fixed semi-subsurface systems. • The size of the hazard – determines the requirements for foam concentrate and water. Carbon dioxide is useful where the minimum damage should be caused to the materials at risk, on fires in liquid, solids or electrical fires but not where there is a high risk of reignition. It is likely to be ineffective outdoors due to rapid dispersal. It is unsuitable for reactive metals, metal hydrides or materials with their own oxygen supply, e.g. cellulose nitrate. Dry powders are effective on flammable liquid or electrical fires. Special powders are available for use on metals. Dry powder extinguishers may be used on Class C fires, including gases and liquefied gases in the form of a liquid spillage or a liquid or gas leak. This must be accompanied by other actions, e.g. stopping the leak; this is necessary to avoid accumulation of an unburned flammable gas–air mixture which could subsequently result in an explosion. Activation may be automatic by a detection system, or manual. Vaporizing liquid halogen agents are electrically non-conductive and are effective on a wide range of combustibles, particularly flammable liquids and electrical fires. A ‘lock-off’ system is required on fixed installations to protect personnel, the normal extinguishing concentration being 5% by volume. The use of such liquids is being phased out; except for defined essential uses they will be banned from 31 December 2003. Portable extinguishers and fire blankets are normally provided at strategic points in the work area. The range of application of portable extinguishers is summarized in Table 6.12. British Standard EN3: Part 5 requires all new extinguisher bodies to be red. A zone of colour above, or within, the section used to provide operating instructions may be used to identify the type of extinguisher. The colours used are: Standard dry powder or multi-purpose dry powder blue AFFF (aqueous film-forming foam) cream Water red Vaporizing liquid, including Halon green Carbon dioxide black Fixed installations for fire-fighting may be either: • Manually operated for general protection, e.g. hose reels, hydrants and foam installations, or • Automatically operated for general protection, e.g. sprinklers, or for special-risk protection, e.g. carbon dioxide installations. The general requirements of such an installation are summarized in Table 6.13. Fire precautions A range of precautions are based on the principles summarized earlier. However, general precautions, applicable to the majority of work situations, are listed in Table 6.14, many of which are included in legal requirements. In the UK duties under the Fire Precautions (Workplace) (Amendment) Regulations 1999 are to: • carry out a fire risk assessment of the workplace; • identify significant findings and details of anyone specifically at risk; FIRE PRECAUTIONS 223 Table 6.12 Portable fire extinguishers Extinguisher type Water Carbon dioxide Dry powder Foam Vaporizing liquid (3) Fire blanket Sand Class A fire Wood, cloth, paper Most suitable Small fires only Small fires only Yes Small fires only (1) No, except for No or similar personal combustible clothing on material fire Cooling by water most effective Class B fire Flammable liquids, Dangerous Most suitable Most suitable Most suitable (2) Small fires only (1) Most suitable Small fires only petrol, oils, Small fires only greases, fats Blanketing/ smothering most effective Electrical plant, electrical Dangerous Most suitable Most suitable No Yes (1) No No installations Non-conductivity of extinguishing agent most important (1) Toxic products may be produced: care must be exercised after use in confined spaces. (2) Special foam required for water-miscible liquids. (3) Subject to replacement. Table 6.13 General requirements for fixed fire-extinguishing systems (Activation may be automatic by a detection system, or manual) • Capability to control and extinguish the anticipated fire condition without recourse to outside assistance (unless planned for). • Reliability, allowing for environmental features likely to be detrimental to operation, e.g. dust, corrosion, tar. • Agents must be compatible with the process, with each other, and with any other installed systems. • Consideration of the potential toxicity of the agent, any thermal degradation products, or products generated on contact with chemicals present will dictate safety measures. • If manual fire-fighting is also anticipated following agent discharge, visibility in the fire zone requires consideration. Table 6.14 General fire precautions Area designation Zoning for electrics Control portable heaters etc. No smoking Restricted areas Electrical equipment Regular inspection and maintenance by qualified electricians Prohibition of makeshift installations Waste disposal Prevention of combustible waste accumulation in corners, passageways or other convenient ‘storage’ areas Storage Segregated storage Uncongested storage of combustibles: gangways/adequate breaks Material stacked in the open should be away from windows Flammable liquids in properly designed storerooms: bulk quantities in fixed, bunded, adequately spaced tanks Contractors Clearance Certificate control of contractors/temporary workers Close control of temporary heating, lighting, cooking etc. Escape/access Escape doors and routes must be kept free of obstructions Access for emergency services must be maintained Fire equipment Fire alarm and fire-fighting equipment must be regularly inspected, maintained and tested Portable extinguishers to have designated locations/be of correct type. Instructions must be provided as to where and how to use them. Practice is necessary Flues Passages for services or other ducts must be adequately fire-stopped to prevent their acting as flues for fire/smoke transmission Sprinklers Maintain sprinkler systems Institute alterations if building is modified, use changes etc. Observe use specifications, e.g. for stack heights, fire loading Prevention of arson Control access at all times Screen employees and casual labour Lock away flammable substances and keep combustibles away from doors, windows, fences Provide regular fire safety patrols, even where automatic systems are provided Secure particularly storage and unmanned areas Fire and smoke stop Ensure that fireproof doors and shutters are self-closing doors Keep all doors free from obstruction Ensure that fire check doors are kept closed FIRE PRECAUTIONS 225 226 FLAMMABLE CHEMICALS 1 Identify fire hazards Sources of ignition Sources of fuel Work processes 2 Identify the location of people at significant risk in case of fire 3 Evaluate the risks Adequacy of existing fire safety measures Control of ignition sources Control of fuel sources Fire detection/warning Means of escape Means of fighting fire Maintenance and testing of fire precautions Fire safety training of all employees Implement any if necessary 4 Record findings and take action Prepare emergency plan Inform, instruct and train all employees in fire precautions 5 Keep assessment under review Revise if situation changes Figure 6.2 Action plan for fire risk assessment • provide and maintain fire precautions to safeguard those at the workplace; • provide relevant information, instruction and training. In the UK the Building Regulations impose fire safety requirements on: • structural stability; • compartmentalization to restrict fire spread; • fire resistance of elements and structures; • reduction of spread of flame over surfaces of walls and ceilings; • space separation between buildings to reduce the risk of fire spread from one building to another; • means of escape in case of fire; • access for fire appliances and assistance to the fire brigade. An action plan for risk assessment is given in Figure 6.2. Table 6.15 Essentials for fire instruction and training Action to be taken upon discovering a fire Action to be taken upon hearing the fire alarm Raising the alarm, including the location of alarm call points, internal fire alarm telephones and alarm indicator panels Correct method of calling the fire service The location and use of fire-fighting equipment Knowledge of the escape routes The importance of fire doors and the need to close all doors at the time of a fire and on hearing the fire alarm Stopping machines and processes and isolating power supplies where appropriate Evacuation of the building: • procedures for alerting visitors, members of the public etc., including if necessary directing/escorting them to exits; • familiarity with how to open all escape doors and the use of any emergency fastenings; • understanding of the reason for not using lifts except those designated, and of special design, for evacuation of disabled persons The minimum fire instruction and training needs are summarized in Table 6.15. FIRE PRECAUTIONS 227 [...]... 428 – – – – 22 0 – – – 26 0–371 – 343 470 445 – 363 24 5 300 23 8 – 309 420 334 – 28 8 3.4– 114 7.3– 101 – 304 2. 6 131 2. 6 120 – 23 2 – 22 0 – 23 8 – 29 0–301 1.0–4 .66 125 – 24 0 – 194 – 178 – 360 – 360 – – – – – – – – – 360 – >370 – – 1.3– 128 0.4– 58 1.4–8 36 1.4–7 .6 28 – 24 0 – 1 36 40 –90 28 60 –108 –93 15 –4.1 52 – –57 16 –17 –39 . 4.07 25 – – 1 26 –43 insol. 10 /24 Diethyl cellosolve 0.8 6. 56 35oc 20 7 – 121 –74 – 9.4 Diethylene glycol 1. 12 3 .66 124 22 9 2 24 5 –8 sol. 1/ 92 Diethylene glycol-monoethyl 1.11 4 .6 96 20 4 1 .2 20 2. –9 – – 94 – 92 insol. – n -Butyraldehyde 0. 82 2.5 6. 7 23 0 2. 5– 76 –99 4 – iso-Butyraldehyde 0.79 2. 5 –40 25 4 1 .6 10 .6 64 66 4 – n -Butyric acid 0. 96 3.0 66 4 52 2–10 164 –7.9 ∞ 0.4 /20 iso-Butyric. 4 .6 71 4 12 1 6 1 82 –81 – 1 /23 iso-Butyl benzene 0.9 4 .6 52 418 1–7 174 –83 – 1/19 n -Butyl bromide 1 .28 4.7 18 26 5 2 6. 6 101 –1 12 0. 06 – Butyl carbitol 1.0 5 .6 78 22 8 – 23 1 68 – 0. 02/ 20 Butyl