Hazardous Chemicals Handbook 2 Episode 6 pot

Control measures Strategies for handling flammable materials • Minimize at the design stage the risk of fire/explosion, e.g.. Selected key tactics for working with flammable chemicals ar

218 FLAMMABLE CHEMICALS

Table 6.9 Pyrophoric chemicals in common use

Pyrophoric alkyl metals Carbonylpotassium Pyrophoric metal Triethylarsine

Alkyl lithiums Dodecacarbonyltetracobalt Barium sulphide Triisopropylphosphine

Diplumbanes Hexacarbonylchromium Chromium (II) sulphide TrimethylboraneTrialkylaluminiums Hexacarbonylmolybdenum Copper (II) sulphide TrimethylphosphineTrialkylbismuths Hexacarbonyltungsten Diantimony trisulphide

Nonacarbonyldiiron Dibismuth trisulphide Pyrophoric alkyl

Bis-dimethylstibinyl oxide Pentacarbonyliron Dicerium trisulphide ButyldichloroboraneBis(dimethylthallium) acetylide Tetracarbonylnickel Digold trisulphide Dichlorodiethylsilane

Diethylberyllium Pyrophoric metals Germanium (II) sulphide Dichlor(ethyl)silaneDiethylcadmium (in finely-divided state) Iron disulphide Dichloro(methyl)silane

Dimethyl-l-propynlthallium Lithium Sodium polysulphide Diethylphosphine

Trimethylthalium Pyrophoric non-metals Tetramethyldiarsine

Uranium carbide

Rarely founduncombined

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

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 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:

flammable-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, lowervapour 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

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).

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:

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.

• 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

Flammable liquids, Dangerous Most suitable Most suitable Most suitable(2) Small fires only(1) Most suitable Small fires only

(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 plannedfor)

• 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 contactwith 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 smokingRestricted 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

Uncongested storage of combustibles: gangways/adequate breaksMaterial stacked in the open should be away from windowsFlammable 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 beprovided 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 labourLock away flammable substances and keep combustibles away from doors, windows, fencesProvide 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 ignitionSources of fuelWork processes

2 Identify the location of people at significant risk in case of fire

3 Evaluate the risks

Adequacy of existing fire safety measuresControl of ignition sources

Control of fuel sourcesFire detection/warningMeans of escapeMeans of fighting fireMaintenance and testing of fire precautionsFire safety training of all employeesImplement any if necessary

4 Record findings and take action

Prepare emergency planInform, instruct and train all employees in fireprecautions

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 panelsCorrect 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 disabledpersons

The minimum fire instruction and training needs are summarized in Table 6.15.

FIRE PRECAUTIONS 227

Table 6.1 Properties of flammable chemicals

Acetylene dichloride, see

1,2-Dichloroethylene

Allylene, see Propyne

2-Aminoethanol, see

Ethanolamine

n-Amyl alcohol 0.82 3.0 33 300 1–10 137 –79 sl sol 1/14

p-Benzoquinone, see Quinone

Benzylidene chloride, see Benzal

Boron hydrides, see Di-, Penta-,

or Deca-Boranes

1-Bromobutane, see Butyl bromide

Bromoethane 1.46 3.76 none 511 6.7–11.3 38 –119 sl sol 400/21Bromomethane, see Methyl

bromide

Bromopentane, see Amyl bromide

Bromopropane, see Propyl

n-Butanol, see n-Butyl alcohol

Butanone, see Methyl ethyl

(air = 1) (°C) (°C) (%) (°C) (°C) (g/100 g) (mm Hg/°C)

Butyl ether, see Dibutyl ether

Caprylic acid, see Octanoic acid

Caprylic alcohol, see 1-Octanol

Carbitol, see Diethylene glycol

Carbonyl sulphide 1.07 2.1 – – 12–29 –50 –138 8014

Carvene, see Dipentene

Chloroethane, see Ethyl chloride

Chloroethanol, see Ethylene

Cresylic acid, see o-Cresol

Table 6.1 Cont’d

(air = 1) (°C) (°C) (%) (°C) (°C) (g/100 g) (mm Hg/°C)

at 10 mm

Diethyl ether, see Ethyl ether

at 11 mm

Table 6.1 Cont’d

(air = 1) (°C) (°C) (%) (°C) (°C) (g/100 g) (mm Hg/°C)

Diethyl sulphate 1.18 5.3 104 436 – 208dec –25 insol 1/47Diglycol, see Diethylene glycol

(at 100°C)

2,2-Dimethyl propane 0.61 2.48 <–7 450 1.4–7.5 9.5 –18 insol 100/21

2-Ethoxy ethanol, see Cellosolve

2-Ethoxy ethylacetate, see

Cellosolve acetate

Ethyl alcohol, see Ethanol

Ethyl aldehyde, see Acetaldehyde

Ethyl bromide, see Bromoethane

Ethyl cyanide, see Propionitrile

Table 6.1 Cont’d

(air = 1) (°C) (°C) (%) (°C) (°C) (g/100 g) (mm Hg/°C)

Ethylene chlorohydrin 1.21 2.78 60oc 425 4.9–15.9 128 –69 ∞ 10/30

Ethylene glycol monobutyl ether,

see Butyl cellosolve

Ethylene glycol monoethyl ether,

see Cellosolve

Ethylene glycol monomethyl

ether, see Methyl cellosolve

Ethylenimine, see Aziridine

Ethyl mercaptan, see Ethanethiol

2-Ethyl-3-propyl acrolein 0.85 4.35 68oc – – 175 <100 insol 1/20