Hazardous Chemicals Handbook 2 Episode 5 potx

Vapours often travel a considerable distance to an ignition source remote from the point of chemical escape.. • Explosion: a confined vapour cloud explosion CVCE can result from ignition

α-Alumina, see Aluminium oxide

Ammonium chloride fume – 10 – 20 – 10 – 20

Antimony and antimony compounds

Butanethiol, see Butyl mercaptan

2-Butanone, see Methyl ethyl ketone

respirable dust, as Cd

10 (totalinhalable dust) –

10 (total

4 (respirable dust)Camphor, synthetic, see Bornan-2-one

Carbonyl chloride, see Phosgene



2-Chloroethanol, see Ethylene

chlorohydrin

Chloroethylene, see Vinyl chloride

Chromium (VI) compounds, as Cr

Chrysotile, see Asbestos

(ppm) (mg/m) (ppm) (mg/m) (ppm) (mg/m) (ppm) (mg/m) (ppm; v/v)

(m-cresol)Cristobalite, see Silica, crystalline

Crocidolite, see Asbestos

1,2-Dibromoethane, see Ethylene

Dichlorophenoxyacetic acid, see 2,4-D

1,2-Dichloropropane, see Propylene

Dihydroxybenzene, see Hydroquinone

Diisopropyl ether, see Isopropyl ether

Dimethoxymethane, see Methylal

Diphenyl ether (vapour),

see Phenyl Ether

Diphenylmethane diisocyanate, see

(ppm) (mg/m) (ppm) (mg/m) (ppm) (mg/m) (ppm) (mg/m) (ppm; v/v)Enzymes, see Subtilisins

1,2-Epoxypropane, see Propylene oxide

2,3-Epoxy-1-propanol, see Glycidol

Ethanethiol, see Ethyl mercaptan

Ethanol, see Ethyl alcohol

Ethylene glycol methyl ether acetate,

see 2-Methoxyethyl acetate

Ferrous foundry particulate

(ppm) (mg/m) (ppm) (mg/m) (ppm) (mg/m) (ppm) (mg/m) (ppm; v/v)Gypsum, see Calcium sulphate

Hexachlorocyclohexane, see Lindane

Hexahydro-1,3,5-trinitro-1,3,5-triazine, see Cyclonite

1,6-Hexanolactam, see Caprolactam

2-Hexanone, see Methyl n-butyl ketone

Hydrogen bromide – – C3 C9.9 – – 3 10 2.0

Hydrogen cyanide and cyanide salts

(excluding cyanogen and cyanogen

Isopropyl glycidyl ether (IGE), see

2,3-Epoxypropyl isopropyl ether

respirable dust)

10 (totalinhalable dust)

Marble, see Calcium carbonate

Mercaptoacetic acid, see

Inorganic forms including

Methanethiol, see Methyl mercaptan

Methanol, see Methyl alcohol

Methylene chloride, see

Dichloro-methane)

Mineral wool fibre – 10 – MEL – –

Nuisance particulates, see Particulates

not otherwise classified (PNOC);

Dusts

Particulate polycyclic aromatic

hydrocarbons (PPAH), see

Coal tar pitch volatiles

2-Pentanone, see Methyl propyl ketone

Pentyl acetate, see Amyl acetates

Perlite – 10 – – – – – –

Petroleum distillates, see Gasoline;

Stoddard solvent; VM&P naphtha

Phenacyl chloride, see

Phenylethylene, see Styrene, monomer

2-Pivalyl-1,3-indandione, see Pindone

Plaster of Paris, see Calcium sulphate

(ppm) (mg/m) (ppm) (mg/m) (ppm) (mg/m) (ppm) (mg/m) (ppm; v/v)Polyvinyl chloride

Propargyl calcohol, see Prop-2-yn-1-ol)

Propylene glycol monomethyl ether,

Pulverized fuel ash

Pyrocatechol, see Catechol

Quartz, see Silica, crystalline

Quinone 0.1 0.44 – – 0.1 0.4 0.3 1.3 0.084RDX, see Cyclonite

Silica, Crystalline (Respirable)

(ppm) (mg/m) (ppm) (mg/m) (ppm) (mg/m) (ppm) (mg/m) (ppm; v/v)Silver

100% pure crystalline enzyme)

Sulphur monochloride, see Disulphur dichloride

Synthetic vitreous fibres

Continuous filament glass fibres

Talc (containing asbestos fibres) Use asbestos

TLV-TWA

TEDP, see Sulfotep

Toluol, see Toluene

Toxaphene, see Chlorinated camphene

Trimellitic anhydride, see

Benzene-1,2,4-tricarboxylic acid 1,2-anhydride

Vinyl benzene, see Styrene

Vinyl cyanide, see Acrylonitrile

MEL Maximum exposure limit

NOC Not otherwise classified

SEN Capable of causing respiratory sensitization; skin sensitizers have not been given a separate notation

SK Can be absorbed through skin

This table is a useful guide but because standards are continually under review and many caveats apply reference should be made to the most recent edition of HSE EH

40 and the AGGIH TLV list for current values and their interpretation Often carcinogens are not assigned a hygiene standard

(a) Parts of vapour or gas per million parts of contaminated air by volume at 25°C and 760 torr (1.013 bar)

(b) Milligrams of substance per m3 air

(c) Value shown is OES unless otherwise indicated as MEL

Simple asphyxiant Some gases and vapours present at high concentrations act as asphyxiants by reducing the oxygen content of air Many of these are odourless andcolourless Many also pose a fire or explosion risk, often at values below which asphyxiation can occur (Although capable of asphyxiation, they are not considered to

be substances hazardous to health under COSHH.)

(e) Suspected human carcinogens – see TLV Appendix A, Category A2 (below)

(f) The value is for total dust containing no asbestos and <1% crystalline silica

(g) Confirmed human carcinogen – see TLV Appendix, A, Category A1 (below)

(h) Fibres longer than 5 µm and with an aspect ratio ≥3:1 as determined by the membrane filter method at 400–450X magnification (4 mm objective) phase contrastillumination

(i) Welding fumes cannot be classified simply The composition and quantity of both are dependent on the alloy being welded and the process and electrodes used.Reliable analysis of fumes cannot be made without considering the nature of the welding process and system being examined; reactive metals and alloys such asaluminium and titanium are arc-welded in a protective inert atmosphere such as argon These arcs create relatively little fume, but they do create an intense radiationwhich can produce ozone Similar processes are used to arc-weld steels, also creating a relatively low level of fumes Ferrous alloys also are arc-welded in oxidizingenvironments that generate considerable fume and can produce carbon monoxide instead of ozone Such fumes generally are composed of discrete particles ofamorphous slags containing iron, manganese, silicon, and other metallic constituents depending on the alloy system involved Chromium and nickel compounds arefound in fumes when stainless steels are arc-welded Some coated and flux-cored electrodes are formulated with fluorides and the fumes associated with them cancontain significantly more fluorides than oxides Because of the above factors, arc-welding fumes frequently must be tested for individual constituents that are likely to

be present to determine whether specific TLVs are exceeded Conclusions based on total fume concentration are generally adequate if no toxic elements are present inwelding rod, metal, or metal coating and conditions are not conducive to the formation of toxic gases

Most welding, even with primitive ventilation, does not produce exposures inside the welding helmet above 5 mg/m3 That which does, should be controlled.(j) UK control limits for asbestos:

Chrysotile 0.3 fibres/ml of air averaged over any continuous 4 hr period

0.9 fibres/ml of air averaged over any continuous 10 min periodAny other form of asbestos, 0.2 fibres/ml of air averaged over any continuous 4 hr period

alone or in mixtures 0.6 fibres/ml of air averaged over any continuous 10 min period

Action levels for cumulative exposures within a 12 week period:

(a) for chrysotile, 72 fibre hours/ml of air

(b) for any other form of asbestos, alone or in mixtures, 48 fibre hours/ml of air

(c) for both types of exposure at different times within the period, a proportionate number of fibre hours/ml

The lack of limits should not be taken to imply an absence of hazard In the absence of a specific OEL for a particular dust, exposure should be adequately controlledand where there is no indication of the need for a lower value, personal exposure should be kept below both 10 mg/m3 8 hr TWA total inhalable dust and 4 mg/m3

8 hr TWA respirable dust

(k) UK limits for lead are 8 hr TWA concentrations as follows:

Lead other than lead alkyls – 0.15 mg/m3 of air

These are ceiling values that must not be exceeded when calculating 8 hr TWA They should be read in conjunction with biological limits for lead

(l) As measured by the vertical elutriator cotton-dust samples

(m) Polytetrafluoroethylene decomposition products: thermal decomposition of the fluorocarbon chain in air leads to the formation of oxidized products containingcarbon, fluorine and oxygen Because these products decompose in part by hydrolysis in alkaline solution, they can be quantitatively determined in air as fluoride toprovide an index of exposure No TLV is recommended pending determination of the toxicity of the products, but air concentration should be minimal (Trade names:Algoflon, Fluon, Teflon, Tetran.)

(n) In the UK vinyl chloride is also subject to an overriding annual maximum exposure limit of 3 ppm

(o) As sampled by a method that does not collect vapour

TLV Appendix A: Carcinogens (excerpts)

The Chemical Substances Threshold Limit Values Committee classifies certain substances found in the occupational environment as either confirmed or suspected human

Two categories of carcinogens are designated:

A1 – Confirmed Human Carcinogens Substances, or substances associated with industrial process, recognized to have carcinogenic potential

A2 – Suspected human carcinogens Chemical substances, or substances associated with industrial process, which are suspect of inducing cancer, based on their limitedepidemiological evidence or demonstration of carcinogenesis in one or more animal species by appropriate methods

Exposures to carcinogens must be kept to a minimum Workers exposed to A1 carcinogens without a TLV should be properly equipped to eliminate to the fullest extentpossible all exposure to the carcinogen For A1 carcinogens with a TLV and for A2 carcinogens, worker exposure by all routes should be carefully controlled to levels

as low as reasonably achievable (ALARA) below the TLV

6 Flammable chemicals

Certain chemicals pose fire and explosion risks because:

• They ignite easily Vapours often travel a considerable distance to an ignition source remote from the point of chemical escape.

• Considerable heat is generated Many volatile substances liberate heat at a rate some ten times faster than burning wood.

• The fire spreads easily by, e.g., running liquid fire, a pool fire, a fire ball, heat radiation or thermal lift (convection).

• Explosion: a confined vapour cloud explosion (CVCE) can result from ignition of vapour within a building or equipment; a boiling liquid expanding vapour explosion (BLEVE) can result when unvented containers of flammable chemicals burst with explosive violence as a result of the build-up of internal pressure; unconfined vapour cloud explosion (UVCE) can result from ignition of a very large vapour or gas/air cloud.

Clearly, flammable chemicals also pose a health risk if the substance or its thermal degradation

or combustion products are toxic, (e.g carbon monoxide) or result in oxygen deficiency because oxygen is consumed Hot smoke and other respiratory irritants, e.g aldehydes, are also produced.

Ignition and propagation of a flame front

Normally flame propagation requires

(a) fuel, gas or vapour (or combustible dust) within certain concentration limits,

(b) oxygen supply (generally from air) above a certain minimum concentration, and

(c) ignition source of minimum temperature, energy and duration.

All three, represented by the three corners of a triangle (Figure 6.1), must generally be present But no ignition source is needed if a material is above a specific temperature (see p 214), and no additional oxygen is required if an oxidizing agent is present or in a few cases when oxygen is within the fuel molecule (e.g ethylene oxide).

Fuel

Liquids and solids do not burn as such, but on exposure to heat vaporize or undergo thermal degradation to liberate flammable gases and vapours which burn Some chemicals undergo spontaneous combustion (see page 214).

Mist/frothDust of combustible solid

Ignition source

Flames

Sparks (of sufficient energy)

Self heating etc

Oxygen

AirOxidizing agentincluding e.g chlorine

Flammable limits

Flammable gases and volatile liquids are particularly hazardous because of the relative ease with which they produce mixtures with air within the flammable range An increase in the surface area

of any liquid facilitates vaporization For each substance there is a minimum concentration of gas

or vapour below which flame propagation will not occur (i.e the mixture is too lean) There is also a concentration above which the mixture is too rich to ignite The limits of flammability are influenced by temperature and pressure (e.g the flammable range expands with increased temperature) Generally, the wider the flammable range the greater the fire risk Flammability limits for a range of chemicals are summarized in Table 6.1.

The vapour pressure of a flammable substance also provides an indication of how easily the material will volatilize to produce flammable vapours; the higher the vapour pressure, the greater the risk Lists of vapour pressures usually contain data obtained under differing conditions but inspection of boiling points (when the vapour pressure equals atmospheric pressure) gives a first approximation of the ease with which substances volatilize Table 6.1 therefore includes both boiling point and vapour pressure data.

Flash point

The flash point represents the minimum temperature at which an ignitable mixture exists above

a liquid surface By definition, flash points are inapplicable to gases Some solids, e.g naphthalene and camphor, are easily volatilized on heating so that flammable mixtures develop above the solid surface and hence flash points can be determined (However, although these substances can be ignited, they generally need to be heated above their flash points in order for combustion to be sustained: this is the ‘fire point’.)

Flash point determinations may be made in ‘closed’ or ‘open’ containers, giving different values;

Figure 6.1 Fire triangle

198 FLAMMABLE CHEMICALS

these are non-equilibrium methods Alternatively equilibrium methods are available Typical flash points are quoted in Table 6.1 and, unless otherwise stated, these relate to closed cup measurements In general, the lower the flash point the greater the potential for fire: materials with flash points at or below ambient temperature are highly flammable and can inflame at ambient temperature on contact with ignition sources Flash point is used to classify liquids under many legislative systems: in the UK liquids with flash points <32 °C (and which, when heated under specific test conditions and exposed to an external source of flame applied in a standard manner, supports combustion) are defined as ‘highly flammable’ under the Highly Flammable Liquid and Liquefied Petroleum Gas Regulations.

Chemicals may ignite below their flash points if the substance:

• Is in the form of a mist (or froth).

• Covers a large surface area (e.g when absorbed on porous media).

• Contains a small amount of a more volatile flammable liquid, e.g due to deliberate or accidental contamination.

in close proximity Storage of flammable chemicals, therefore, needs careful consideration.

Vapour density

The density of a vapour or gas at constant pressure is proportional to its relative molecular mass and inversely proportional to temperature Since most gases and vapours have relative molecular masses greater than air (exceptions include hydrogen, methane and ammonia), the vapours slump and spread or accumulate at low levels The greater the vapour density, the greater the tendency for this to occur Gases or vapours which are less dense than air can, however, spread at low level when cold (e.g release of ammonia refrigerant) Table 6.1 includes vapour density values.

Dust explosions

Increasing the surface area of a combustible solid enhances the ease of ignition Hence dust burns more rapidly than the corresponding bulk solid; combustion of dust layers can result in rapid flame spread by ‘train firing’ Solid particles less than about 10 µm in diameter settle slowly in air and comprise ‘float dust’ (see p 51 for settling velocities) Such particles behave, in some ways, similarly to gas and, if the solid is combustible, a flammable dust–air mixture can form within certain limits Larger particles also take part, since there is a distribution of particle sizes, and ignition can result in a dust explosion.

Dust explosions are relatively rare but can involve an enormous energy release A primary

explosion, involving a limited quantity of material, can distribute accumulations of dust in the

atmosphere which, on ignition, produces a severe secondary explosion.