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

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from an appliance in which the flame has been extinguished. Any fire near an LPG cylinder may

cause it to overheat and catch fire, or result in a BLEVE with missiles projected over long

distances.

The following safety measures supplement the general precautions listed in Table 9.3:

• Do not store or use a cylinder on its side, but upright with the valve uppermost.

• Do not store or leave full or empty cylinders below ground level.

• Never change a cylinder without first closing the cylinder valve and extinguishing naked lights

in the vicinity.

Table 9.15 Properties of LPGs

Propane Butane isoButane

Molecular weight 44.1 58.1 58.1

Vapour pressure at 21°C, i.e. cylinder 7.7 1.15 21.6

pressure (kg/cm

gauge)

Specific volume at 21°C/l atm (ml/g) 530.6 399.5 405.8

Bp at 1 atm (°C) –42.07 –0.5 –11.73

Mp at 1 atm (°C) –187.69 –138.3 –159.6

SG, gas at 16°C/l atm (air = 1) 1.5503 2.076 2.01

Density, liquid at sat. pressure (g/ml) 0.5505 0.5788 0.563

(20°C) (20°C) (15°C)

Density, gas at 0°C/l atm (kg/m

) 2.02 2.70 –

Critical temperature (°C) 96.8 152 135

Critical pressure (atm) 42 37.5 37.2

Critical density (g/ml) 0.220 0.225 0.221

Latent heat of vap. at bp (cal/g) 101.76 92.0 87.56

Latent heat of fusion at mp (cal/g) 19.10 19.17 18.67

Specific heat, liquid at 16°C (cal/g°C) – 0.5636 0.5695

Specific heat, gas at 16°C:

(cal/g°C) 0.3885 0.3908 0.3872

(cal/g°C) 0.3434 0.3566 0.3530

ratio

1.13 1.1 1.1

Specific heat ratio at 16°C/l atm, C

1.131 1.096 1.097

Gross heat of combustion at 16°C/l atm 22.8 30.0 29.8

(cal/ml)

Viscosity, gas at 1 atm (centipoise) 0.00803 0.0084 0.00755

(16°C) (15°C) (23°C)

Coefficient of cubical expansion at 15°C 0.0016 0.0011 –

(per °C)

Surface tension (dynes/cm) 16.49 16.02 15.28

(–50°C) (–10°C) (–20°C)

Solubility in water at 1 atm (volumes/100 6.5 – 1.7

volumes water) (18°C) – (17°C)

Flammable limits in air (% by volume) 2.2–9.5 1.9–8.5 1.8–8.4

Autoignition temp. (°C) 467.8 405 543

Max. explosion pressure (MPa) 0.86 0.86 –

Min. ignition energy (MJ) 0.25 0.25 –

Max. flame temperature (°C) 2155 2130 –

Max. burning velocity (m/s) 0.45 0.38 –

Necessary min. inert gas conc. for explosion

prevention in case of emergent outflow of gas

in closed volumes (% v/v):

Nitrogen 45 41 –

Carbon dioxide 32 29 –

LIQUEFIED PETROLEUM GASES (LPG) 289

290 COMPRESSED GASES

1000

500

100

300

149

200

100

°F25

–4°C

Temperature

Vapour pressure (psia)

• Store cylinders, both full and empty, in a cool location away from flammable, toxic, or corrosive

materials and preferably at least 6.1 m from any source of ignition or heat.

• Replace any valve-protecting covers on empty cylinders, or those not in use. Handle cylinders

with care.

• Unless the installation is designed to be permanent, always disconnect a cylinder after use.

• Always wear appropriate protective equipment, including gloves and goggles, when filling an

LPG cylinder.

Figure 9.6

n-Butane vapour pressure vs temperature

The general requirements for the storage of LPG cylinders are given in Tables 9.16 to 9.18.

Considerations in the transport of cylinders by road are given in Chapter 15.

Methane

Methane is obtained commercially from natural gas wells and from cracking of petroleum fractions.

Figure 9.7

Propane vapour pressure vs temperature

1000

100

1501000–100°F

6637–18–73°C

Temperature

Vapour pressure (psia)

METHANE 291

292 COMPRESSED GASES

Table 9.16 General requirements for storage of LPG cylinders

• Store in the open in a well-ventilated area at ground level.

• Avoid other materials stacked near restricting natural ventilation.

Flammable liquid and combustible, corrosive, oxidizing or toxic substances and compressed gases should be kept

separately.

• Avoid cylinders impeding or endangering means of escape from premises or from adjoining premises.

• The store floor should be level. A load-bearing surface (concrete, paved or compacted) is required where cylinders are

to be stacked.

• Security arrangements should be such as to prevent tampering or vandals. Fencing should be of robust wire mesh which

does not obstruct ventilation.

• The area should be at the separation distance from the property boundary, any building or fixed source of ignition quoted

in Table 9.17. This may only be reduced if suitable fire-resisting separation is provided.

• To give additional protection from thermal radiation from any cylinder stack fire the minimum separation distance to any

nearby building housing a vulnerable population should, for quantities >400 kg, be 8 m or as in Table 9.17, column 3,

whichever is the greater. This may be reduced to those in Table 9.17, column 4, by the installation of fire-resisting

separation or a fire wall.

• Prohibit all sources of ignition, including smoking, within a store or within the separation distance (exclude motor

vehicles other than fork-lift trucks and those for delivery/collection from open-air stores).

• Avoid openings into buildings, cellars, or pits within 2 m or the separation distances, whichever is greater. (Any gully or

drain unavoidably within 2 m should have the opening securely covered or fitted with a water seal to prevent vapour

ingress.)

• Electrical equipment suitable for a Zone 2 area (e.g. to BS 5345) and constructed to a recognized standard should be

installed within the store and separation distance. Zone 2 areas are summarized in Table 9.18.

• Clearly mark the area with notices indicating an LPG storage area, flammable contents, prohibition of ignition sources

and procedures to follow in case of fire.

• Avoid accumulation of rubbish, small bushes, dry leaves etc. within the separation distance. Remove weeds and long

grass within the separation distance and up to 3 m from cylinders.

• Cylinders should be stored upright with the valves closed with any protective cover, cap or plug in place. Cartridges

without valves may be stored on their sides.

• Cylinders on a vehicle or trailer parked overnight rate as a single stack so that the separation distance in Table 9.17,

column 3, is applicable.

• Cylinders received into store and taken out for delivery should be checked for damage or leakage. Stacks should be

inspected daily for stability and that they contain no damaged/leaking cylinders.

• Cylinders should be handled carefully to avoid personal injury or damage to them.

The physical properties of methane are given in Table 9.19 and the relationship between pressure

and temperature in Figure 9.8. It is considered to be non-toxic but is an asphyxiant at high

concentrations. Coalminers have inhaled air containing up to 9% methane with no apparent

untoward effect but higher concentrations of at least 10% in air result in a feeling of pressure on

the eyes and forehead which will disappear after breathing fresh air. Characteristic symptoms of

asphyxiation occur at higher concentrations (i.e. rapid respiration, fatigue, nausea, vomiting

possibly leading to loss of consciousness and anoxia). At low concentrations the odour of methane

is undetectable; at exposures of >5000 ppm there is a sweet oil-type odour. Selected grades

contain an odorizer, e.g. natural gas for commercial and domestic full.

It is considered to be chemically inert at room temperature and atmospheric pressure but it does

react under more forcing conditions and vigorous reactions have occurred with halogens, interhalogen

compounds, and oxidizing agents such as liquid oxygen and dioxygen difluoride.

The main hazard is that of flammability. The following precautions supplement those in Table

9.3 for the storage of methane gas cylinders:

• Store in a purpose-built compound preferably in the open air and well ventilated.

• Locate free from fire risk and away from sources of heat and ignition.

• Maintain clear access, and restrict access to the compound. Mark with hazard warning signs.

• Prohibit the use of naked flames or smoking in the vicinity of, or inside, the compound.

• Store separately from oxygen and oxidants, using a fire-resistant partition where necessary.

• Store the minimum quantity practicable.

• Check periodically for general condition and leakage.

Nitrogen

Nitrogen is an odourless, colourless gas which comprises ca 79% by volume of air and is an

essential constituent of all living organisms, e.g. as protein. It is made in the laboratory by gently

Table 9.17 Recommended minimum separation distances for total storage of LPG in cylinders or size of maximum

stack (the greater of the two distances is advised)

(1) (2) (3) (4)

Total quantity LPG store Size of largest stack Minimum separation Minimum separation

distance to boundary, distance to boundary,

building or fixed building or fixed ignition

ignition sources from the source from fire wall

nearest cylinder (where (where provided)* **

no fire wall provided)

(kg) (kg) (m) (m)

From 15 to 400 1*** Nil

,, 400 to 1000 Up to 1000 3 1

,, 1000 to 4000 4 1

,, 4000 to 6000 From 1000 to 3000 5 1.5

,, 6000 to 12 000 6 2

,, 12 000 to 20 000 ,, 3000 to 5000 7 2.5

,, 20 000 to 30 000 ,, 5000 to 7000 8 3

,, 30 000 to 50 000 ,, 7000 to 9000 9 3.5

,, 50 000 to 60 000 ,, 9000 to 10 000 10 4

,, 60 000 to 100 000 11 4.5

,, 100 000 to 150 000 ,, 10 000 to 20 000 12 5

,, 150 000 to 250 000 ,, 20 000 to 30 000 15 6

Above 250 000 20 7

*The distance from the nearest cylinder to a boundary, building etc. should be not less than in column 3 when measured

around the fire wall.

**Minimum distance from nearest cylinder to fire wall should normally be 1.5 m except as qualified.

***No separation distance is required for these quantities where boundary walls and buildings are of suitable construction.

Table 9.18 Areas classified as requiring Zone 2 electrical equipment

Location Extent of classified area

Storage in open air In the storage area up to a height of 1.5 m above the top of the

stack or beneath any roof over the storage place.

Outside the storage area or the space covered by any roof up to

1.5 m above ground level and within the distance set out for a

fixed source of ignition in Table 9.17, column 3.

Storage within a specially designed building or in The entire space within the building or storage area and outside

a specially designed storage area within a building any doorway, low level ventilator or other opening into the

store within the separation distance set out in Table 9.17,

column 3, up to a height of 1.5 m above ground level.

NITROGEN 293

294 COMPRESSED GASES

–110–150–200–250°C

–79–102–129–157°F

Temperature

1000

300

100

Vapour pressure (psia)

warming a concentrated solution of equimolar proportions of ammonium chloride and sodium

nitrite:

Cl + NaNO

→ NaCl + NH

→ N

+ 2H

On the industrial scale nitrogen is obtained by the fractional distillation of liquid air (see page

261). It will neither burn nor support combustion. Nitrogen is distributed as a pressurized gas in

grey cylinders with black shoulders. (Oxygen-free nitrogen has opposed white spots on the

cylinder shoulder.) It finds wide use in its inert capacity, e.g. in electrical equipment and in the

chemical and food industries. Large volumes of atmospheric nitrogen are converted into ammonium

sulphate for fertilizer and into nitric acid.

Figure 9.8

Methane vapour pressure vs temperature

Since it is chemically inert no special materials of construction are required. Selected physical

properties are listed in Table 9.20.

Nitrogen is non-toxic but will cause asphyxiation through oxygen depletion of air and is the

most common cause of gassing accidents in industry. There are no warning signs before

unconsciousness occurs, and at high concentrations almost instant unconsciousness may occur

and prove fatal (page 77). Table 5.7 summarizes the health effects of oxygen-deficient atmospheres.

Nitrogen oxides

The various oxides of nitrogen are given in Chapter 5.

Nitrous oxide is a colourless, non-flammable, non-corrosive gas with a sweetish odour and

taste. It is prepared both in the laboratory and on a commercial scale by heating ammonium

nitrate:

→ N

O + 2H

Heating must be terminated when two-thirds of the nitrate has decomposed since explosive

nitrogen trichloride may be formed from traces of ammonium chloride impurity.

Nitrous oxide may also be obtained by the controlled reduction of nitrates or nitrites, decomposition

of hyponitrites, or thermal decomposition of hydroxylamine.

It is generally considered not to be toxic and non-irritating. One of its main applications is, in

combination with air or oxygen, as a weak anaesthetic in medicine and dentistry. At low concentrations

it produces hysteria (hence the term laughing gas). At high concentrations in the absence of air it

is a simple asphyxiant. It is also used as a dispersing agent in whipping cream.

It does not react with oxygen, ozone, hydrogen, chlorine, potassium, phosphine or aqua regia.

However, whilst stable at ordinary temperatures, it decomposes readily to oxygen and nitrogen at

600°C and therefore supports combustion of burning substances. When nitrous oxide is transferred

from a stock cylinder to smaller cylinders the gas expansion results in cooling and a reduction in

pressure. On heating the stock container to increase pressure and thereby facilitate transfer the gas

Table 9.19 Physical properties of methane

Molecular weight 16.04

Specific volume @ 21°C 1479.5 ml/g

Boiling point @ 1 atm –161.5

Freezing point @ 1 atm –182.6°C

Triple point –182.5°C

Triple point pressure 0.115 atm

Specific gravity (gas) @ 16°C, 1 atm 0.5549

Density (gas) @ 0°C, 1 atm 0.72 g/l

Density (liquid) @ bp 0.4256 g/l

Critical temperature –82.1°C

Critical pressure 673.3 psia (45.8 atm)

Critical density 0.162 g/ml

Latent heat of vaporization @ bp 121.54 cal/g

Specific heat (gas) @ 16°C, 1 atm

1.307

Flammable limits in air 5.3–14%

Autoignition temperature 540°C

Minimum ignition energy 0.28 mJ

Flame temperature 1880°C

Limiting oxygen index 11.5%

Viscosity (gas) @ 1 atm, 4.4°C 0.0106 cP

NITROGEN OXIDES 295

296 COMPRESSED GASES

decomposes causing explosive rupture of the stock cylinder. This emphasizes the importance of

keeping cylinders away from heat sources, e.g. oxyacetylene welding operations. Explosive reaction

has also occurred between nitrous oxide and a variety of chemicals including amorphous boron,

ammonia, carbon monoxide, hydrogen, hydrogen sulphide, and phosphine. Because the oxygen

content of 36.4% is higher than the 21% in air, combustion or oxidation in nitrous oxide is much

faster than in air.

It is transported in high pressure steel cylinders equipped with brass valves.

Physical properties are summarized in Table 9.21 and the vapour pressure/temperature relationship

is depicted by Figure 9.9. The general precautions in Table 9.3 apply.

Nitric oxide is made commercially by oxidation of ammonia above 500°C in the presence of

platinum, or by reduction of nitrous acid with ferrous sulphate or ferrous halides. The physical

Table 9.20 Physical properties of nitrogen

Molecular weight 28.0134

Specific volume @ 21°C 861.5 ml/g

Boiling point @ 1 atm –195.8°C

Triple point –210.0°C

Triple point pressure 94.24 mm Hg

Density (gas) @ 20°C 1.250 g/l

Density (liquid) @ bp 0.8064 g/ml

Critical temperature –147.1

Critical pressure 33.5 atm

Critical density 0.311 g/ml

Latent heat of vaporization @ bp 47.51 cal/g

Specific heat (gas) @ 16°C, 1 atm

0.2477 cal/g°C

0.1765 cal/g°C

ratio

1.4

Viscosity (gas) @ 15°C, 1 atm 0.01744 centipoises

Dielectric constant (liquid) @ bp 1.433

Solubility in water @ 0°C 2.3 ml/100 ml water

Table 9.21 Physical properties of nitrous oxide

Molecular weight 44.013

Vapour pressure @ 21°C 745 psig

Specific volume @ 21°C, 1 atm 543 ml/g

Boiling point @ 1 atm –89.5°C

Freezing point @ 1 atm –90.84°C

Specific gravity (gas) @ 15°C, 1 atm 1.530

Density (gas) @ 0°C, 1 atm 1.907 g/l

Density (liquid) @ bp 1.266 g/l

Critical temperature 36.5°C

Critical pressure 1054 psia (71.7 atm)

Critical density 0.457 g/l

Latent heat of vaporization @ bp 89.9 cal/g

Specific heat gas @ 25°C, 1 atm

0.2098 cal/g°C

0.1610 cal/g°C

ratio

1.3

Viscosity (gas) @ 0°C, 1 atm 0.01362 centipoise

Solubility in water @ 0°C, 1 atm 1.3 volumes/volume of water

1300

1000

500

100

1000–60–80°F 60

38–18–51–62°C 16

Temperature

Vapour pressure (psia)

properties of nitric oxide are given in Table 9.22. This is also a colourless, non-flammable gas

which is basically non-corrosive to standard materials of construction. Liquid nitric oxide like

other cryogenic oxidizers (e.g. ozone) is very sensitive to detonation in the absence of fuel. It is

the simplest molecule that is capable of detonation in all three phases: the liquid oxide may

explode during distillation. Nitric oxide is more toxic than nitrous oxide. It decomposes into its

elements only when heated to 1000°C and therefore it is not a ready supporter of combustion.

Vigorously burning phosphorus continues to burn in the gas but burning sulphur or charcoal is

extinguished.

Figure 9.9

Nitrous oxide vapour pressure vs temperature

NITROGEN OXIDES 297

298 COMPRESSED GASES

Nitric oxide combines readily with atmospheric oxygen at ambient temperature to produce

brown fumes of pungent nitrogen dioxide, and in the presence of charcoal with chlorine to form

nitrosyl chloride:

2NO + O

→ NO

2NO + Cl

→ 2NOCl

It is shipped in cylinders as a non-liquefied gas at a pressure of about 500 psig at 21°C and is

primarily used as a chemical intermediate (e.g. in production of nitric acid). It is somewhat

soluble in water producing nitric acid, making the gas slightly irritating to the lower reaches of

the respiratory system and mucous membranes causing congestion to the throat, bronchi and

oedema of the lungs with little warning. The acids neutralize alkali in tissue with subsequent

adverse effect on blood pressure, producing headaches and dizziness. The OEL is 25 ppm (8 hr

TWA) and 35 ppm (15 min STEL), but generation of the more toxic dioxide on release to air is

always a major consideration.

Some special safety measures include:

• Handle only in well-ventilated areas, preferable with a hood equipped with forced ventilation.

• Provide adequate number of exits from the work area.

• Use approved personal protection as appropriate, including self-contained breathing apparatus

and associated training.

• Provide suitable first-aid cover.

• Prevent air contamination in high-pressure reactions since the nitrogen dioxide which could

form may pose ignition and detonation hazards.

Gaseous nitrogen dioxide is a brown, paramagnetic, non-flammable, toxic, strongly oxidizing,

corrosive substance shipped in approved, low-pressure steel cylinders. It is prepared in situ by

heating lead nitrate:

2Pb(NO

)

→ 2PbO + 4NO

+ O

It is available commercially from several routes including as a product from the manufacture of

sodium nitrate from sodium chloride and nitric acid, and from a process involving the passage of

ammonia and air over heated platinum and treating the nitric oxide so formed with oxygen.

Table 9.22 Physical properties of nitric oxide

Molecular weight 30.006

Specific volume @ 21°C, 1 atm 811 ml/g

Boiling point @ 1 atm –151.7°C

Freezing point @ 1 atm –163.6°C

Density (gas) @ 0°C, 1 atm 1.3402 g/l

Density (liquid) @ bp 1.269 g/l

Critical temperature –93°C

Critical pressure 940.8 psia (64 atm)

Critical density 0.52 g/ml

Latent heat of vaporization @ bp 110.2 cal/g

Specific heat (gas) @ 15°C, 1 atm

0.2328 cal/g°C

0.1664 cal/g°C

ratio

1.4

Viscosity (gas) @ 15°C 1 atm 0.0178 cP

Solubility in water @ 0°C, 1 atm 7.34 ml/100 g water