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

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The brown nitrogen dioxide gas condenses to a yellow liquid which freezes to colourless

crystals of dinitrogen tetroxide. Below 150°C

the gas consists of molecules of dinitrogen tetroxide

and nitrogen dioxide in equilibrium and the proportion of dinitrogen tetroxide

increases as the

temperature falls. Above 150°C nitrogen dioxide dissociates into nitric oxide and oxygen.

Nitrogen dioxide is an oxidizing agent; it gives up all, or part, of its oxygen to reducing agents,

leaving a residue of nitrogen and nitric oxide. It reacts with potassium, hydrogen sulphide,

mercury, burning phosphorus or carbon, heated iron and copper. Explosions have been reported

between nitrogen dioxide and a host of materials including alcohols (to produce alkyl nitrates),

boron compounds, carbonyl metals, propyl nitrite, nitroaniline dust, sodium amide, triethylamine,

and vinyl chloride.

Nitrogen dioxide reacts with water, giving first a mixture of nitrous and nitric acids, and

ultimately nitric acid and nitric oxide:

O + 2NO

→ HNO

+ HNO

O + 3NO

→ 2HNO

+ NO

When dry the gas is not corrosive to mild steel at normal temperatures and pressures. Metals and

alloys such as carbon steel, stainless steel, aluminium, nickel and Inconel are satisfactory. For wet

usage stainless steels resistant to 60% nitric acid are suitable. Important uses include use as a

bleaching agent, an oxidation catalyst, polymerization inhibitor, a nitrating agent, oxidizing agent,

rocket fuel, and in explosives manufacture. Its physical properties are summarized in Table 9.23

and its vapour pressure/temperature relationship is shown in Figure 9.10.

Table 9.23 Physical properties of nitrogen dioxide

Molecular weight 46.005 (or 92.01 for the tetroxide)

Vapour pressure @ 21°C 14.7 psia

Specific volume @ 21°C, 1 atm 293.4 ml/g

Boiling point @ 1 atm 21.25°C

Freezing point @ 1 atm –9.3°C

Specific gravity (gas) @ 20°C, 1 atm 1.58

Density (gas) @ 21°C, 1 atm 3.3 g/l

Density (liquid) @ 20°C 1.448 g/ml

Critical temperature 158.0°C

Critical pressure 1470 psia (100 atm)

Critical density 0.56 g/ml

Latent heat of vaporization @ bp 99.0 cal/g

Specific heat (gas) @ 25°C, 1 atm

0.1986 cal/g °C

Viscosity (liquid) @ 20°C 4.275 millipoises

A key feature of its toxicity (page 154) at low concentrations is the delay between exposure and

onset of symptoms. The OES is 3 ppm (8 hr TWA) and 5 ppm (15 min STEL). Effects of exposure

are summarized in Table 5.33. Chronic exposures to low concentrations may cause chronic

irritation of the respiratory tract with cough, headache, loss of weight, loss of appetite, dyspepsia,

corrosion of the teeth and gradual loss of strength. Concentrations above 60 ppm produce immediate

irritation of the nose and throat with coughing, choking, headache, shortness of breath and

restlessness. Even brief exposures above 200 ppm may prove fatal. Liquid nitrogen dioxide

(dinitrogen tetroxide) is corrosive to skin.

First-aid measures include removal from the contaminated atmosphere, rest and administration

of pure oxygen. Skin or eyes in contact with liquid should be thoroughly irrigated. Medical

attention should be sought. Other special precautions include:

NITROGEN OXIDES 299

300 COMPRESSED GASES

1000

500

200

100

20015010070°F

93663721°C

Temperature

Vapour pressure (psia)

• Handle in well-ventilated area, preferably with hood equipped with forced extract ventilation.

• Ensure adequate number of emergency exits.

• Consider the need for personal protection such as skin, eye (goggles/face shield) and respiratory

protection including self-contained breathing apparatus.

• Provide instant-acting safety showers and eye-wash facilities in the location of the work

area.

• Train staff in appropriate first-aid measures including how to seek immediate medical assistance.

Figure 9.10

Nitrogen dioxide vapour pressure vs temperature

Oxygen

Oxygen occurs free in air in which it forms 21% by volume. It is also found combined with

hydrogen in water and constitutes 86% of the oceans, and with other elements such as minerals

constituting ca 50% of the earth’s crust. In the laboratory it is usually prepared by the thermal

decomposition of potassium chlorate in the presence of manganese dioxide catalyst:

2KClO

→ 2KCl + 3O

Industrially, it is manufactured either by fractional distillation of air, or by electrolysis of sodium

hydroxide and it is distributed as a non-liquefied gas in pressurized black cylinders at ca 2200 psig

at 21°C. Since it is non-corrosive no special materials of construction are required.

Selected physical properties of oxygen are included in Table 9.24. It is a colourless, odourless

and tasteless gas which is essential for life and considered to be non-toxic at atmospheric pressure.

It is somewhat soluble in water and is slightly heavier than air. Important uses are in the steel and

glass industries, oxyacetylene welding, as a chemical intermediate, waste-water treatment, fuel

cells, underwater operations and medical applications.

Table 9.24 Physical properties of oxygen

Molecular weight 32.00

Specific volume @ 21°C, 1 atm 755.4 ml/g

Boiling point @ 1 atm –183.0

Triple point –218.8°C

Density (gas) @ 0°C, 1 atm 1.4291 g/l

Density (liquid) @ bp 1.141 g/l

Critical temperature 1118.4°C

Critical pressure 737 psia (50.14 atm)

Critical density 0.427 g/l

Latent heat of vaporization @ bp 50.94 cal/g

Specific heat (gas) @ 15°C, 1 atm

0.2200 cal/g°C

0.1554 cal/g°C

ratio

1.42

Viscosity (gas) @ 25°C, 1 atm 0.02064 centipoise

Solubility in water @ 0°C, 1 atm 1 volume/21 volumes water

Explosive reactions can occur between oxygen and a wide range of chemicals including organic

compounds (such as acetone, acetylene, secondary alcohols, hydrocarbons), alkali and alkaline

earth metals, ammonia, biological specimens previously anaesthetized with ether, hydrogen and

foam rubber.

Oxygen supports combustion and the hazard is increased if the concentration in air exceeds

21% (page 199) or at pressures above atmospheric pressure. Substances ignite more readily, burn

at a faster rate, generate higher temperatures and may be extremely difficult to extinguish. Substances,

e.g. plastics, clothing or metals, which may not normally burn easily can burn vigorously in

oxygen-enriched air. Oxygen may become trapped within clothing; this can then be ignited and

cause serious burn injuries. Because some substances, e.g. oil and grease, may react explosively

with pressurized oxygen it is important never to use lubricants on oxygen equipment and to free

pipelines from deposits of them.

Enrichment of the atmosphere in any workplace to about 25% oxygen can be hazardous; this

is particularly so in a confined space. Inhalation of 100% oxygen at atmospheric pressure for

OXYGEN 301

302 COMPRESSED GASES

16 hr per day for several days poses no undue problems but longer periods of exposure to high

pressures can adversely affect neuromuscular coordination and the power of concentration.

In addition to the control measures given in Table 9.3, the following precautions are appropriate

when using industrial and medical oxygen, or mixtures of oxygen with other gases.

Never:

• Use oxygen to sweeten the air of a workplace.

• Use oxygen instead of fresh air to ventilate or cool a confined space.

• Use oxygen instead of compressed air or as a source of pressure, e.g. to clear blockages in

pipelines or to power air-driven tools.

• Use oxygen to blow down clothing, benches or machinery.

• Use oxygen to inflate vehicle tyres, rubber boats etc.

• Use oxygen to start a diesel engine.

• Use oxygen to cool the person.

• Use oil or grease on oxygen equipment.

• Use jointing compound or tape to cure leaks in oxygen equipment, e.g. at cylinder connections.

• Cut off the supply of oxygen by nipping or kinking flexible hose when changing equipment.

Always:

• Only use materials and equipment which are suitable for oxygen service and to a recognized

standard.

• Regularly check equipment for signs of leaks, e.g., at hose connections; replace damaged or

worn items. Usually the system is pre-tested with, e.g., nitrogen.

• Ensure that equipment, e.g. pipework for oxygen service, is kept clean and free from oil, grease

or dust.

• Ensure that the rated maximum inlet pressure of the regulator is not less than the cylinder

supply pressure. (For cylinder pressures up to 200 bar, pressure regulators should comply with

BS 5741. For higher cylinder pressures check with the manufacturer that the pressure regulator

has been shown to be suitable by appropriate testing.)

• Ensure that the pressure adjusting screw of a pressure regulator is fully unwound, so that the

regulator outlet valve is closed before opening the oxygen cylinder valve.

• Open cylinder valves slowly.

• Ensure that the cylinder valves are closed and piped supplies isolated whenever work is stopped.

• Ensure that flexible oxygen hose for welding etc. complies with BS 5120. The correct colour

for oxygen is blue.

• Ensure that proper fresh air ventilation is provided in oxy-fuel gas welding and cutting operations.

• Ensure that high-pressure oxygen systems are designed, constructed, installed and commissioned

by competent people with specialized knowledge of the subject.

• When working on ships, remove pipes or hoses when work stops, other than for short intervals.

• Store oxygen cylinders in a well-ventilated area or compound away from combustible materials

and separated from cylinders of flammable gases.

• Handle oxygen cylinders carefully, preferably using a purpose-built trolley and keep secured to

prevent cylinders from falling.

• Wear protective clothing appropriate to the work, e.g. leather gloves, fire-retardant overalls,

safety shoes or boots and eye protection.

• If applicable, locate oxygen cylinders outside any confined space and in an area of good

ventilation.

Ozone

Ozone is an allotrope of oxygen containing three oxygen atoms. It occurs naturally in the upper

atmosphere and is formed in small quantities during electrical discharges from electrical machines

or when white phosphorus smoulders in air. In the laboratory it is most conveniently obtained by

subjecting air to electrical discharges in ‘ozonizers’ when some of the oxygen molecules dissociate

into oxygen atoms which then combine with other oxygen molecules. However, the yield of

ozone is only 10% even when pure oxygen is used. It may also be prepared by electrolysis of ice-

cold dilute sulphuric acid using a high current density. Here the concentration of ozone liberated

at the platinum-in-glass anode is about 14%.

Pure ozone is made by fractional distillation of the blue liquid resulting from the cooling of

ozonized oxygen in liquid air. Commercially it is often supplied dissolved in chlorofluorocarbons

in stainless steel cylinders at ca 475 psig cylinder pressure at 20°C often transported chilled with

dry ice. These solutions can be handled safely at vapour concentrations of ca 20% by volume of

ozone.

The physical properties of ozone are summarized in Table 9.25.

Table 9.25 Physical properties of ozone

Molecular weight 47.998

Boiling point @ 1 atm –111.9°C

Freezing point @ 1 atm –192°C

Density (gas) @ 0°C, 1 atm 2.143 g/l

Density (liquid) @ –183°C 1.571 g/l

Critical temperature –12.1°C

Critical pressure 802.6 psia (54.6 atm)

Viscosity (liquid) @ –183°C 1.57 cP

Latent heat of vaporization @ bp 3410 cal/mole

Dielectric constant (liquid) @ –183°C 4.79

Dipole moment 0.55D

Solubility in water @ 0°C, 1 atm 0.494 volume/volume of water

Ozone is strongly exothermic in its reactions and neat solid or liquid phases are highly explosive.

Pure ozone is a toxic, slightly bluish, unstable, non-flammable but potentially explosive gas

with a smell akin to that of much-diluted chlorine. It is used mainly because of its extreme

oxidizing ability (second only to fluorine in oxidizing power) in chemical syntheses or because

of its powerful germicidal activity on many bacterial organisms, e.g. as a water purification agent

(e.g. swimming pools) although it may leave an unpleasant taste, as a bleach, in treatment of

industrial waste, sterilization of air (e.g. in the ventilation of premises of underground railways

with limited access to fresh air), deodorizing sewage and stack gases, and in food preservation.

Indeed, algae and certain fungi resistant to chlorine are highly susceptible to ozone. It decomposes

slowly at room temperature and rapidly at 200°C and is decomposed by many finely-divided

metals. It reacts readily with unsaturated organic moieties to form ozonides:

—CH

CH—R

+ O

→

—CH CH—R

O O

(Ozonide)

OZONE 303

304 COMPRESSED GASES

where R

and R

are univalent organic groups.

Violent reactions have occurred between ozone and many chemicals, a small selection being

acetylene, alkenes, dialkyl zincs, benzene/rubber solution, bromine, carbon monoxide and ethylene,

diethyl ether, hydrogen bromide, and nitrogen oxide.

Ozone is an irritant to eyes and mucous membranes. Inhalation can cause pulmonary oedema

and bleeding at ‘high’ concentrations, whilst at lower exposures symptoms include headache,

shortness of breath, or drowsiness. Long-term effects may include chronic pulmonary effects,

ageing, and possibly lung cancer. The ACGIH classify ozone as one of those ‘Agents which cause

concern that they could be carcinogenic for humans but which cannot be assessed conclusively

because of the lack of data. In vitro or animal studies do not provide indications of carcinogenicity

which are sufficient to classify the agent into one of the other categories.’ The TLV is set as a

sliding scale for exposures during different workloads, thus:

• 0.05 ppm for heavy work.

• 0.08 ppm for moderate work.

• 0.10 ppm for light work.

• 0.20 ppm for heavy, moderate, or light workloads for up to a maximum exposure of 2 hours.

Because of the odour threshold of ca 0.015 ppm, exposure to ozone below the TLV can usually

be detected by smell.

Precautions in addition to those in Table 9.3 include:

• Keep cylinders chilled (to help prevent decomposition rather than as a safety measure).

• Avoid copper and copper alloys since these can catalyse the decomposition, and rubber components

are unsuitable.

• Pre-test systems for leaks with inert gas.

• Prevent contact with grease, oil or other combustible material.

• Clean all equipment for oxygen service.

• Handle in a ventilated hood to protect surrounding atmosphere from leaks.

• Consider the need for appropriate personal protection including eye, skin and respiratory

equipment.

• Consider the need for leak detection systems.

• Where possible avoid explosions by working with dilute solutions at low temperatures in

suitable solvents.

Sulphur dioxide

Sulphur dioxide is used as a preservative for beer, wine and meats; in the production of sulphites

and hydrosulphites; in solvent extraction of lubricating oils; as a general bleaching agent for oils

and foods; in sulphite pulp manufacture; in the cellulose and paper industries; and for disinfection

and fumigation.

It is a non-flammable colourless gas which is twice as dense as air, and slightly soluble in water

forming sulphurous acid. It is readily liquefied as a gas under its own vapour pressure of about

35 psig (2.4 bar) at 21°C. Figure 9.11 depicts the effect of temperature on vapour pressure; Table

9.26 lists the physical properties. Cylinders tend to be protected against over–pressurization by

metal plugs melting at about 85°C.

Gaseous sulphur dioxide is highly irritant and practically irrespirable. Effects on the body are

summarized in Table 5.3. It can be detected at about 3.5 ppm and the irritating effects would

2752502252001751501251007550250–25–50°F

13512110793796652372510–4–18–32–46°C

Temperature

1000

900

800

700

600

500

400

300

200

100

Vapour pressure (psia)

Boiling point

Figure 9.11

Sulphur dioxide vapour pressure vs temperature

preclude anyone from suffering prolonged exposure at high concentrations unless unconscious, or

trapped.

Liquid sulphur dioxide may cause eye and skin burns resulting from the freezing effects upon

evaporation. Dry sulphur dioxide is non-corrosive to common materials of construction except

zinc. The presence of moisture renders the environment corrosive.

In addition to the precautions listed in Table 9.3, the following controls are appropriate:

• Use in well-ventilated areas.

SULPHUR DIOXIDE 305

306 COMPRESSED GASES

Table 9.26 Physical properties of sulphur dioxide

Molecular weight 64.063

Vapour pressure at 21°C 2.37 bar

Specific volume at 21°C, 1 atm 368.3 ml/g

Boiling point at 1 atm –10.0°C

Freezing point at 1 atm –75.5°C

Specific gravity, gas at 0°C, 1 atm (air = 1) 2.264

Density, gas at 0°C, 1 atm 2.927 g/l

Density, liquid at –10°C 1.46 g/ml

Critical temperature 157.5°C

Critical pressure 78.8 bar

Critical density 0.524 g/ml

Latent heat of vaporization at boiling point 92.8 cal/g

Latent heat of fusion at melting point 27.6 cal/g

Specific heat, liquid at 0°C 0.318 cal/g °C

Specific heat, gas at 25°C, 1 atm

0.1488 cal/g °C

0.1154 cal/g °C

ratio

1.29

Thermal conductivity at 0°C 2.06 × 10

–5

cal/s cm

°C/cm

Viscosity, gas at 18°C, 1 atm 124.2 mP

Solubility in water at 0°C, 1 atm 18.59% by weight

at 20°C, 1 atm 10.14% by weight

• Wear eye/face protection, approved footwear and rubber gloves.

• Showers and eye-wash facilities and respiratory protection should be conveniently located for

emergencies.

• Insert traps in the line to avoid liquid suck-back into the cylinder.

• Check for leaks with soap solution, aqueous ammonia or colour indicator tubes.

• First aid measures include those in Table 9.9.

Monitoring techniques

As mentioned in Chapters 4, 5 and 16 chemicals can be a nuisance or pose safety, health and

environmental risks, or become wasteful of expensive resources if allowed to escape excessively

and uncontrollably into the general or workplace environment. Escapes can result from inadequate

process control, errors in operation or maintenance, incomplete understanding of the process, etc.

Such problems can arise from both: periodic emissions of chemicals due to the need to open, or

enter, the ‘system’ occasionally (e.g. during sampling, cleaning, line-breaking) including both

planned and unplanned releases (e.g. due to accidents, human error) and, continuous low-level

fugitive emissions from normally-closed points, e.g. valve seals, flange gaskets, pump seals, drain

valves.

The need to monitor the impact of activities involving chemicals on the environment may stem

from sound management practice or to satisfy a host of specific legal requirements. Thus, in the

UK under the Environmental Protection (Prescribed Substances and Processes) Regulations 1991,

operators must apply BATNEEC to prevent or minimize the release of prescribed substances into

the environment, or to render harmless any emissions. The prescribed substances for release into

the air are given in Table 10.1. No prescribed process may be operated without an authorization

from the Environment Agency and air pollutants which must be measured and the frequency of

monitoring are set out in the authorization. Compliance with emission limits for municipal waste

incineration plants (Table 10.2) also requires monitoring.

Table 10.1 Prescribed substances for release into the air

Oxides of sulphur and other sulphur compounds

Oxides of nitrogen and other nitrogen compounds

Oxides of carbon

Organic compounds and partial oxidation compounds

Metals, metalloids and their compounds

Asbestos, glass fibres and mineral fibres

Halogens and their compounds

Phosphorus and its compounds

Particulate matter

In addition to pollution episodes, risks may arise due to atmospheric oxygen concentrations

fluctuating beyond its normal level of 21% posing health (page 72) or fire hazards. Fire and

explosion dangers may also arise from the presence of flammable gases, vapours, or dusts in the

atmosphere (Chapter 6).

Thus, as illustrated by Table 17.13 monitoring emissions of hazardous chemicals into the

environment may be required for a variety of reasons such as:

308 MONITORING TECHNIQUES

• Assessing fire or explosion risks from atmospheres containing flammable gas, vapour or dust.

• Determining oxygen content of the working atmosphere.

• Determining sources of leaks of toxic, flammable, or nuisance pollutants.

• Identifying unknown pollutants.

• Assessing process efficiency and control.

• Assessing environmental risk from effluent discharges or for formal environmental impact

assessment.

• Determining employee exposure to known toxic substances.

• Providing data for internal company environmental audits.

• Investigation of the causes of accidents.

• Investigation of the cause and nature of problems (e.g. local complaints of odour) or pollution

incidents.

Selected general analytical techniques for

monitoring environmental pollution

Stages in environmental monitoring include obtaining representative samples of the environment

in question and subsequent analysis of physical, chemical or microbiological attributes. Monitoring

techniques range from sophisticated in-line, continuous sampling and instantaneous analysis

linked to audible/visual alarms or features to control the pollution; samplers running continuously,

e.g. throughout a normal day for subsequent analysis; to grab samples (i.e. samples collected over

a short time span of, e.g., a few minutes). Continuous monitoring is common in personal dosimetry

studies where an appropriate collection device samples air wherever a worker is throughout a

specified period, e.g. 15 minutes or 8 hours (page 111). A selection of common analytical techniques

include the following.

Gases and vapours

Atomic absorption/emission spectrometry

Metal ions are most commonly measured using atomic absorption spectrometry. In this technique

Table 10.2 Selected emission limits for municipal waste incineration (units: mg/m

)

Country EU EU EU UK UK

Plant capacity 3 1–3 <1 >1 <1

(tonne per hour)

Particulates 30 100 200 30 200

CO 100 100 100 100 100

300 300 – 300 300

Volatile organic 20 20 20 20 20

compounds

HF 2 4 – 2 –

as NO

– – – 350 –

Cr, Cu, Mn, Pb 5 5 –

Ni, As 1 1 – 1 (incl Sn)

Cd, Hg 0.2 0.2 – 0.1 each

Dioxins – – – 1

}