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

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Silver, platinum and Galvanized pipe or brass or

tantalum, carbon, graphite bronze fittings

for wet gas. At higher

pressures use extra heavy

black iron pipe. High-

pressure steel, Monel or

aluminium-iron-bronze valves

Hydrogen selenide F T Aluminium and stainless

steel are preferred but iron,

steel or brass are acceptable

Hydrogen sulphide F T Aluminium preferred. Iron and steel Many metals in the presence of

are satisfactory. Brass, though moist gas

tarnished, is acceptable

Isobutane F Most common metals

Isobutylene F Most common metals

Krypton Most common metals

Methane F Most common metals

Methyl acetylene F Most common metals Copper, silver, mercury and

their alloys

Methylamine C F T Iron and steel Copper, tin, zinc and their

alloys. Avoid mercury

Methyl bromide C F T Most common metals when dry Aluminium and its alloys

3-Methyl-1-butane F Most common metals

Methyl chloride F T Most common metals when Zinc, magnesium rubber and

dry neoprene particularly when

moist. Aluminium is forbidden

Methyl fluoride F T Most common metals

Methyl mercaptan F T Stainless steel and copper-free

steel alloys and aluminium.

Iron and steel for dry gas

Methyl vinyl ether F Most common metals Copper and its alloys

Neon Most common metals

Nickel carbonyl F T Most common metals for pure gas.

Copper or glass-lined equipment

for carbonyl in the presence

of carbon monoxide

Nitric oxide T O Most common metals for dry

gas. For moist gas use

18:8 stainless steel, PTFE

Nitrogen Any common metal

Nitrogen dioxide C T O Most common metals for dry

gas. For moist gas use

18:8 stainless steel

Nitrogen trifluoride T O Nickel and Monel are Plastics

preferred. Steel, copper

and glass are acceptable at

ordinary temperatures

Nitrogen trioxide C T O Steel for

dry

gas otherwise

use 18:8 stainless steel

Nitrosyl chloride C T O Nickel, Monel and Inconel. For

moist gas tantalum is suitable

Nitrous oxide O Most common metals

Octofluorocyclobutane T Cast iron and stainless steel <120°C, Avoid the metals opposite

steel ≤175°C, Inconel, nickel >500°C

and platinum ≤400°C

Oxygen O Most common metals On grease or combustible

COMPRESSED GASES 269

Table 9.1 Cont’d

Gas Hazard

(1)

Materials of construction for ancillary services

(2)

Compatible Incompatible

270 COMPRESSED GASES

Oxygen difluoride T O Glass, stainless steel, copper, materials

Monel or nickel ≤200°C. At

higher temperatures only

nickel and Monel are

recommended

Ozone F T O Glass, stainless steel, Teflon, Copper and its alloys, rubber or

Hypalon, aluminium, any composition thereof, oil,

Tygon, PVC and polythene grease or readily combustible

material

Perchloryl fluoride T Most metals and glass for dry Many gasket materials are

gas at ordinary embrittled

temperatures At higher temperatures many

organic materials and some

metals can be ignited

Some metals such as titanium

show deflagration in contact

with the gas under severe shock

Perfluorobutane Most common materials

Perfluorobutene T Most common materials when dry

Perfluoropropane Most common metals

Phosgene C T Common metals for dry gas.

Monel, tantalum or glass

lined equipment for moist gas

Phosphine F T Iron or steel

Phosphorus pentafluoride F T Steel, nickel, Monel and Pyrex for

dry gas. For moist gas hard

rubber and paraffin wax

Phosphorus trifluoride Steel, nickel, Monel and the

more noble metals and

Pyrex for dry gas

Propane F Most common metals

Propylene F Most common metals

Propylene oxide F T Steel or stainless steel Rubber

preferred though copper

and brass are suitable for

acetylene-free gas. PTFE gaskets

Silane F T Iron, steel, copper, brass

Silicone tetrafluoride C T Most common metals for the

dry gas. Steel, Monel and

copper for moist gas

Sulphur dioxide C T O Most common metals for dry gas. Zinc

Lead, carbon, aluminium and

stainless steel for moist gas

Sulphur hexafluoride Most common metals.

Copper, stainless steel and

aluminium are resistant to

the decomposition

products at 150°C

Sulphur tetrafluoride C T Stainless steel or ‘Hastelloy Glass for moist gas

C’ lined containers. Glass

suitable for short exposures

if dry. ‘Tygon’ for low-pressure

connections

Sulphuryl fluoride T Any common metal at normal Some metals at elevated

temperatures and pressures temperatures

Tetrafluoroethylene F Most common metals

Table 9.1 Cont’d

Gas Hazard

(1)

Materials of construction for ancillary services

(2)

Compatible Incompatible

Tetrafluorohydrazine T O Glass, stainless steel, copper or

nickel to temperatures of 200°C.

For higher temperatures use

nickel and Monel

Trichlorofluoromethane T Steel, cast iron, brass, Some of the opposite at high

copper, tin, lead, temperatures magnesium

aluminium under normal, alloys and aluminium coating

dry conditions >2% magnesium. Natural rubber

1,1,2-Trichloro-1,2,2- As above As above

trifluoroethane

Trimethylamine C F T Iron, steel, stainless steel and Copper, tin, zinc and most of

Monel. Rigid steel piping their alloys

Vinyl bromide F T Steel Copper and its alloys

Vinyl chloride C F T Steel Copper and its alloys

Vinyl fluoride F Steel Copper and its alloys

Xenon Most common materials

C Corrosive

F Flammable

T Toxic

O Oxidizing

(1)

Even non-toxic gases are potentially hazardous owing to asphyxiation (oxygen deficiency). Irrespective of material, all

equipment must be adequately designed to withstand process pressures.

(2)

This is a guide and is no substitute for detailed literature.

To prevent interchange of fittings between cylinders of combustible and non-combustible

gases, the valve outlets are screwed left-hand and right-hand thread, respectively (Table 9.2).

Primary identification is by means of labelling with the name and chemical formula on the

shoulder of the cylinder. Secondary identification is by use of ground colours on the cylinder

body. Unless specified in Table 9.2, gas and gas mixtures shall be identified by a colour classification

indicating gas properties in accordance with the risk diamond on the cylinder label e.g.

Toxic and/or corrosive Yellow

Flammable Red

Oxidizing Light blue

Inert (non-toxic, non-corrosive, Bright green

non-flammable, non-oxidizing

The full scheme is given in BS EN 1089–3: 1997.

This should be consulted for the colour coding of gas mixtures used for inhalation e.g. medical

and breathing apparatus mixtures containing oxygen.

COMPRESSED GASES 271

Table 9.1 Cont’d

Gas Hazard

(1)

Materials of construction for ancillary services

(2)

Compatible Incompatible

Table 9.2 Specific colour codes for selected compressed gases

Gas Colour

Acetylene Maroon

Argon Dark green

Carbon dioxide Grey

Helium Brown

Oxygen White

Nitrogen Black

Nitrous oxide Blue

272 COMPRESSED GASES

Table 9.3 General precautions for handling compressed gases

Consult the supplier for data on the specification, properties, handling advice and on suitable service materials for individual

gases.

Storage

Segregate according to hazard.

Stores should be adequately ventilated and, ideally, located outside and protected from the weather.

Store away from sources of heat and ignition.

Cylinders within workplaces should be restricted to those gases in use. Specially designed compartments with partitions may

be required to protect people in the event of explosion. Take into account emergency exits, steam or hot water systems,

the proximity of other processes etc. Consider the possibility of dense gases accumulating in drains, basements, cable

ducts, lift shafts etc.

Where necessary, provide fireproof partitions/barriers to separate/protect cylinders.

Protect from mechanical damage.

All cylinders must be properly labelled and colour coded (BS 349).

Store full and empty cylinders separately.

Use in rotation: first in, first out.

Restrict access to the stores to authorized staff.

Display ‘No smoking’ and other relevant warning signs.

Ensure that all staff are fully conversant with the correct procedures when using pressure regulators. (For cylinders without

handwheel valves, the correct cylinder valve keys should be kept readily available, e.g. on the valve. Only use such keys.

Do not extend handles or keys to permit greater leverage; do not use excessive force, e.g. hammering, when opening/

closing valves or connecting/disconnecting fittings. The pressure regulator must be fully closed before opening the

cylinder valve. This valve can then be opened slowly until the regulator gauge indicates the cylinder pressure but should

not be opened wider than necessary. The pressure regulator can then be opened to give the required delivery pressure.

When a cylinder is not in use, or is being moved, the cylinder valve must be shut. When a cylinder has been connected,

the valve should be opened with the regulator closed; joints should then be tested with soap/detergent solution.)

Clearly and permanently mark pressure gauges for use on oxygen. Do not contaminate them with oil or grease or use them

for other duties.

Cylinders that cannot be properly identified should not be used; do not rely on colour code alone.

Never try to refill cylinders.

Never use compressed gas to blow away dust or dirt.

Provide permanent brazed or welded pipelines from the cylinders to near the points of gas use. Select pipe materials suitable

for the gas and its application. Any flexible piping used should be protected against physical damage. Never use rubber

or plastic connections from cylinders containing toxic gases.

On acetylene service, use only approved fittings and regulators. Avoid any possibility of it coming into contact with copper,

copper-rich alloys or silver-rich alloys. (In the UK use at a pressure greater than 600 mbar g must be notified to HM

Explosives Inspectorate for advice on appropriate standards.)

On carbon dioxide service, rapid withdrawal of gas may result in plugging by solid CO

. Close the valve, if possible, to allow

the metal to warm up; this will prevent a sudden gas discharge.

Replace the correct caps or guards on cylinder valves when not in use and for return to the supplier.

Test and inspect cylinders and pressure regulators regularly in accordance with current legislation.

Design and manage cylinder stores in accordance with suppliers’ recommendations.

Wear appropriate personal protection when entering any store.

Inspect condition of cylinders regularly, especially those containing hazardous gases (e.g. corrosive).

Use

Transport gases in specially designed trolleys and use eye protection, stout gloves (preferably textile or leather) and protective

footwear.

Do not roll or drop cylinders off the backs of wagons; never lift cylinders by the cap.

Ideally, depending on the length of pipe run, locate cylinders outside (for hazardous gases, valves installed within the

workplace can be used for remote control of the main supply from the cylinder in the event of an emergency). Site

cylinders so that they cannot become part of an electrical circuit.

Securely clamp, or otherwise firmly hold in position, cylinders on installation. (Unless otherwise specified, cylinders containing

liquefied or dissolved gases must be used upright.)

Avoid subjecting cylinders containing liquid to excessive heat.

Table 9.3 provides general guidance for handling compressed gases.

The hazards and safety precautions for selected common compressed gases are discussed

below to illustrate the general approach. More details should be sought from suppliers. Some

methods for their preparation in situ are noted; full experimental details must be obtained from

the literature.

Acetylene

Acetylene is manufactured by the controlled reaction between water and calcium carbide:

CaC

+ 2H

O → Ca (OH)

+ C

Alternatively it is obtained from cracking low molecular-weight aliphatic hydrocarbons, or by the

partial oxidation of natural gas.

Because of its high chemical reactivity, acetylene has found wide use in synthesis of vinyl

chloride, vinyl acetate, acrylonitrile, vinyl ethers, vinyl acetylene, trichloro- and tetrachloro-

ethylene etc., in oxyacetylene cutting and welding, and as a fuel for atomic absorption instruments.

Acetylene is a simple asphyxiant and anaesthetic. Pure acetylene is a colourless, highly flammable

gas with an ethereal odour. Material of commercial purity has an odour of garlic due to the

presence of impurities such as phosphine. Its physical properties are shown in Table 9.4. Acetylene,

which condenses to a white solid subliming at –83

C, is soluble in its own volume of water but

highly soluble in acetone.

Under certain conditions acetylene can explode when mixed with air, hydrogen or ethylene.

Accidental heating of a small area of cylinder wall to 185

C or above may promote an extremely

dangerous condition. Violent reactions have occurred between acetylene and oxidants such as

oxides of nitrogen (see later), nitric acid, calcium hypochlorite, ozone and halogens. In the free

state acetylene can decompose violently, e.g. above 9 psig (0.62 bar) undissolved (free) acetylene

will begin to dissociate and revert to its constituent elements. This is an exothermic process which

can result in explosions of great violence. For this reason acetylene is transported in acetone

contained in a porous material inside the cylinder. Voids in the porous substance can result from

settling, e.g. if the cylinder is stored horizontally or through damage to the cylinder in the form

of denting. Voids may enable acetylene to decompose, e.g. on initiation by mechanical shock if

the cylinder is dropped.

Fit approved cylinder pressure regulators, selected to give a maximum pressure on the reduced side commensurate with the

required delivery pressure. (The regulator and all fittings upstream of it must be able to withstand at least the maximum

cylinder pressure.)

Fit in-line flame arresters for flammable gases and eliminate ignition sources.

Use compatible pipe fittings. (Flammable gas cylinders have valves with left-hand threads; cylinders for oxygen and non-

flammable gases, except occasionally helium, have valves with right-hand threads. Certain liquefied gas cylinders have

two supply lines, one for gas and one for liquid, dependent on cylinder position.)

Do not use oil, grease or joining compounds on any fittings for compressed gas cylinders.

Fit an excess flow valve to the outlet of a regulator, selected to allow the maximum required gas flow.

Use respirators and face protection etc. when changing regulators on cylinders of toxic gases.

Turn off gas supply at the cylinder at the end of each day’s use.

Consider the need for gas detection/alarms, e.g. for hazardous gases left in use out of normal hours.

Periodic checks:

Ensure no gas discharge when gauge reading is zero

Ensure reading on gauge does not increase as the regulator valve is closed

Check for ‘crawl’ due to wear on the regulator valve and seat assembly

Ensure no leak between cylinder and regulator

Overhaul regulators on a 3–6 month basis for corrosive gases, annually for others

Train staff in hazards and correct handling procedures.

ACETYLENE 273

Table 9.3 Cont’d

274 COMPRESSED GASES

Table 9.4 Physical properties of acetylene

Molecular weight 26.038

Vapour pressure of pure liquid at 21°C (not cylinder pressure) 43.8 bar

Specific volume at 15.6°C, 1 atm 902.9 ml/g

Boiling point at 1.22 atm –75°C

Sublimation point at 1 atm –84.0°C

Triple point at saturation pressure –80.8°C

Specific gravity, gas at 15.6°C, 1 atm (air = 1) 0.9057

Density, gas at 0°C, 1 atm 1.1709 g/l

Critical temperature 36.3°C

Critical pressure 62.4 bar

Critical density 0.231 g/ml

Latent heat of sublimation at –84°C 193.46 cal/g

Latent heat of fusion at triple point 23.04 cal/g

Flammable limits in air 2.5–81.0% by volume

Auto-ignition temperature 335°C

Gross heat of combustion at 15.6°C, 1 atm 13.2 cal/cc

Specific heat, gas at 25°C, 1 atm

0.4047 cal/g°C

0.3212 cal/g °C

ratio

1.26

Thermal conductivity, gas at 0°C 4.8 × 10

–5

cal/s cm

°C/cm

Viscosity, gas at 25°C, 1 atm 0.00943 cP

Entropy, gas at 25°C, 1 atm 1.843 cal/g °C

Solubility in water at 0°C, 1 atm 1.7 vol/vol H

Figure 9.1 illustrates the rise in cylinder pressure with temperature. Normally, acetylene cylinders

are fitted with a fusible metal plug which melts at about 100°C.

Acetylene can form metal acetylides, such as copper or silver acetylide, which on drying

become highly explosive: service materials require careful selection.

In addition to the general precautions for compressed gases in Table 9.3, the following control

measures should be considered for acetylene:

• Never use free acetylene at pressures above 9 psig (0.62 bar) unless special safety features are

employed.

• Store and use cylinders only in an upright position.

• Store reserves separate from oxygen cylinders.

• Ensure that no means of accidental ignition are in the area and provide adequate ventilation.

• Consult local regulations for use of this gas.

• Ensure that ‘empty’ cylinders have the valve closed to prevent evaporation of acetone.

• Close cylinder valve before shutting off regulator, to permit gas to bleed from regulator.

• When used e.g. for welding, avoid the careless use of flame which could fuse the metal safety

plug in the cylinder.

• In the event of fire issuing from the cylinder, close the gas supply if it is safe to do so and

evacuate the area.

• Consider the need for detection/alarm systems and in any event check periodically for leaks

with e.g. soap solution, never with a naked flame.

Air

The physical properties of air are given in Table 9.5. Air is a mixture of nitrogen, oxygen, argon,

500

400

300

200

100

30 40 50 60 70 80 90 100 110 120

–1 41016212732 384349

°F

°C

Temperature

Pressure (psia)

carbon dioxide, water vapour, rare gases and trace quantities of ozone, oxides of nitrogen, acetylene,

methane and other hydrocarbons. Its composition varies with altitude. Dry air is inert in its effect

on metals and plastics. The hazards associated with compressed air, in addition to those associated

with any pressure system (i.e. the potential for rupture of equipment or pipework), are:

• From inhalation at pressures above atmospheric, used in tunnelling or diving, or from breathing

apparatus or resuscitation equipment, if the pressure is too high or exposure is prolonged. This

may cause symptoms from pain to dyspnoea, disorientation and unconsciousness; it may be

fatal.

• From particulate matter blown from orifices or surfaces, e.g. into the eyes.

• From entry into any of the body orifices, which can result in serious internal damage.

• From penetration of unbroken skin, or cuts. Foreign matter, e.g. grease, metal, concrete, may

also be injected into subcutaneous tissues.

• From whipping of an unsecured hose on rapid gas release.

Figure 9.1

Acetylene (in acetone): full cylinder pressure versus temperature

Table 9.5 Physical properties of air

Density @ 20°C, 1 atm 0.0012046 g/l

Critical temperature –140.6°C

Critical pressure 546.8 psia (37.2 atm) (38.4 kg/cm

absolute)

Critical density 0.313 g/ml

Viscosity @ 0°C, 1 atm 170.9 micropoises

AIR 275

276 COMPRESSED GASES

The precautions include:

• Prohibition on playing around with compressed air hoses, e.g. aiming directly at any individual.

• Avoidance of blowing away dust or dirt from equipment, the floors, or clothing etc. (which

may also produce a dust inhalation or explosion hazard).

• Direction of the exhaust air from tools away from the operator.

• Proper training and instruction for anyone required to use air-fed breathing apparatus. Restriction

of exposures to compressed air to safe levels.

Ammonia

Ammonia can be made on a small scale by heating an intimate mixture of ammonium chloride

and dry slaked lime in a ratio of 1:3, respectively:

Ca(OH)

+ 2NH

Cl → CaCl

+ 2NH

+ 2H

Industrially, production is either from the Haber process at high pressure:

+ 3H

→ 2NH

or the cyanamide process

CaC

+ N

→ CaCN

+ C

CaCN

+ 3H

O → 2NH

+ CaCO

At room temperature and atmospheric pressure ammonia is a colourless, alkaline gas with a

pungent smell. It dissolves readily in water. Physical properties are summarized in Table 9.6. The

effect of temperature on vapour pressure of anhydrous ammonia is shown in Figure 9.2.

Ammonia is shipped as a liquefied gas under its own vapour pressure of 114 psig (7.9 bar) at

21°C. Uses are to be found in refrigeration, fertilizer production, metal industries, the petroleum,

chemical and rubber industries, domestic cleaning agents and water purification. Aqueous solutions

of ammonia are common alkaline laboratory reagents; ca 0.88 solution is the strongest available.

Ammonia gas is expelled on warming.

Ammonia gas is irritating to the eyes, mucous membranes and respiratory tract. Because of its

odour few individuals are likely to be unwittingly over-exposed for prolonged periods. Table 9.7

summarizes the physiological effects of human exposure. Clearly at high concentrations the gas

becomes corrosive and capable of causing extensive injuries. Thus 1% in air is mildly irritating,

2% has a more pronounced effect and 3% produces stinging sensations.

On contact with the skin, liquid ammonia produces severe burns compounded by frostbite due

to the freezing effect from rapid evaporation from the skin.

Moist ammonia attacks copper, tin, zinc and their alloys. Ammonia is also flammable with

flammability limits of 15–28%.

Ammonia can also react violently with a large selection of chemicals including ethylene oxide,

halogens, heavy metals, and oxidants such as chromium trioxide, dichlorine oxide, dinitrogen

tetroxide, hydrogen peroxide, nitric acid, liquid oxygen, and potassium chlorate.

Besides the control measures given in Table 9.3, the following precautions are appropriate:

• Wear rubber gloves, chemical goggles and, depending upon scale, a rubber apron or full

chemical suit.

• Never heat ammonia cylinders directly with steam or flames to speed up gas discharge.

• Use under well-ventilated conditions and provide convenient safety showers and eye-wash

facilities.

• Ensure that gas cannot be accidentally ignited.

• Check for leaks, e.g. with moist litmus paper or concentrated hydrochloric acid (which forms

dense white fumes of ammonium chloride).

• In the event of accident, administer first aid (see Table 9.9).

Carbon dioxide

Carbon dioxide is present in air and is a constituent of natural gas escaping from mineral springs

and fissures in the earth’s surface. It is also the ultimate product of combustion of carbon and its

compounds. Laboratory scale preparation usually entails reaction between dilute hydrochloric

acid and marble (calcium carbonate):

2HCl + CaCO

→ CaCl

+ H

O + CO

Industrially, it is obtained as a by-product of fermentation of sugar to alcohol:

→ 2C

OH + 2CO

or by burning coke/limestone mixture in a kiln:

CaCO

→ CO

+ CaO

Table 9.6 Physical properties of ammonia

Molecular weight 17.031

Vapour pressure at 21°C (cylinder pressure) 7.87 bar

Specific volume at 21°C, 1 atm 1.411 ml/g

Boiling point at 1 atm – 33.35°C

Triple point at 1 atm – 77.7°C

Triple point pressure 1.33 mbar

Specific gravity, gas at 0°C, 1 atm (air = 1) 0.5970

Density, gas at boiling point 0.000 89 g/ml

Density, liquid at boiling point 0.674 g/ml

Critical temperature 132.44°C

Critical pressure 113 bar

Critical density 0.235 g/ml

Flammable limits in air 15–28% by volume

Latent heat of vaporization at boiling point 327.4 cal/g

Specific heat, liquid at –20°C 1.126 cal/g K

Specific heat, gas at 25°C, 1 atm

0.5160 cal/g°C

0.4065 cal/g °C

ratio,

1.269

Thermal conductivity, gas at 25°C, 1 atm 5.22 × 10

–5

cal/s cm

°C/cm

Entropy, gas at 25°C, 1 atm 2.7 cal/g °C

Heat of formation, gas at 25°C –648.3 cal/g

Solubility at 0°C, 1 atm

in water 42.8% by weight

in methanol, absolute 29.3% by weight

in ethanol, absolute 20. 95% by weight

Viscosity, gas at 0°C, 1 atm 0.009 18 cP

Viscosity, liquid at –33.5°C 0.266 cP

CARBON DIOXIDE 277

278 COMPRESSED GASES

Boiling point

2252001751501251007550250–25–50–75–100°F

10793796652372510–4–18–32–46–60–73°C

Temperature

1000

900

800

700

600

500

400

300

200

100

Vapour pressure (psia)

Liquid carbon dioxide is discussed on page 261. Carbon dioxide gas is commonly used for

carbonating drinks, in fire extinguishers, for gas-shielding of welding and in shell moulding in

foundries. Its physical and toxicological properties are summarized in Tables 8.5, 8.6 and 5.29.

The gas is non-flammable, and is used for inert gas purging. Because it is 1.5 times

heavier than air it may accumulate at low level. The general handling precautions are those in

Table 9.3.

Figure 9.2

Ammonia vapour pressure versus temperature