Carson Ph., Mumford C. Hazardous Chemicals Handbook (Справочник по опасным химическим веществам)

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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

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