33. Chemical accident

Strong toxic substance is the primary hazard of chemical accident. The most

widely used strong toxic substances are chlorine, ammonia, sulfuric anhydride,

hydrogen sulfide, hydrocyanic acid, benzol, mercury.

Chlorine (Cl2): green-yellow gas with strong smell. Boiling point – 34.6 deg

C. Peack concentration 0.1 mg/l is fatal.

Technologic use: producing hydrochloric acid, bleaching, sterilization of

potable water and deactivation of wastes.

Health effects: inflammation of tissues where they are deposited. It may

cause reactions like eczema or dermatitis, shortness of breath, inflammatory

responses and oedema.

Ammonia (NH3): colorless gas with strong smell. It becomes liquid

at temperature -33.4 deg C, solid – at -77.8 deg C. 30-minutes exposure to

concentration 7 mg/l is fatal. It becomes liquid at relatively low pressure 0.7-0.8

MPa.

Since ammonia vaporizing absorbs essential amount of heat it is used in

cooling systems.

Health effects: cramps and inflammation of lungs and larynx which can be

fatal. Skin burns.

Sulfuric anhydride (SO2): colorless gas with strong smell. It becomes liquid

at temperature -10 deg C, solid – at -75 deg C. Twice heavier than air. Reaction

with air gives sulfuric acid. It’s produced by burning sulfur.

Technologic use: production of sulfuric acid, bleaching in papermaking and

fabric making, conservation in food industry, disinfection.

Health effects: coughing, eyes pain, difficult respiring and swallowing, skin

Inflammation.

Hydrogen sulfide (H2S): colorless gas with strong smell. It becomes liquid

at temperature -60.3 deg C, solid – at -85.5 deg C. 4-45% airborne concentration is

explosive. It’s produced as secondary product in petroleum or natural gas refining.

Technologic use: producing sulfuric acid, sulfur.

Medical use: sulfurated hydrogen baths (revitalizing health effect).

Health effects: irritating respiration organs, skin and mucous membranes.

Hydrocyanic acid (HCN): colorless light liquid, has almond fragrance.

Health effects: loss of consciousness, paralysis of respiratory tract.

Benzol (C6H6): colorless liquid, its vapor is heavier than air and explosive.

Health effects: weakness, headache, dizziness, sickness, muscle cramp.

Mercury (Hg): metal that is liquid at room temperature. Its vapor is

poisonous. Mercuric chloride used in dressing skin is very toxic.

To assess risk associated with chemical accident one should consider

exposure, dose and response.

Toxicity is the intrinsic capacity of a chemical agent to affect an organism

adversely.

Xenobiotics is a term for “foreign substances”, that is, foreign to the

organism. Its opposite is endogenous compounds. Xenobiotics include drugs,

industrial chemicals, naturally occurring poisons and environmental pollutants.

Hazard is the potential for the toxicity to be realized in a specific setting or

situation.

A dose is often expressed as the amount of a xenobiotic entering an

organism (in units such as mg/kg body weight). The dose may be expressed in

different (more or less informative) ways:

1. exposure dose, which is the air concentration of pollutant inhaled during a

certain time period (in work hygiene usually eight hours),

2. or the retained or absorbed dose (in industrial hygiene also called the body

burden), which is the amount present in the body at a certain time during

or after exposure.

3. The tissue dose is the amount of substance in a specific tissue

4. and the target dose is the amount of substance (usually a metabolite)

bound to the critical molecule. The target dose can be expressed as mg

chemical bound per mg of a specific macromolecule in the tissue.

To apply this concept, information on the mechanism of toxic action on the

molecular level is needed. The target dose is more exactly associated with the toxic

effect. The exposure dose or body burden may be more easily available, but these

are less precisely related to the effect.

In the dose concept a time aspect is often included, even if it is not always

expressed. The theoretical dose according to Haber's law is

D = CT,

(21)

where D is dose, C is concentration of the xenobiotic in the air and T the duration

of exposure to the chemical. If this concept is used at the target organ or molecular

level, the amount per mg tissue or molecule over a certain time may be used. The

time aspect is usually more important for understanding repeated exposures and

chronic effects than for single exposures and acute effects.

Latency time is the time between first exposure and the appearance of a

detectable effect or response. The term is often used for carcinogenic effects,

where tumours may appear a long time after the start of exposure and sometimes

long after the cessation of exposure.

A dose threshold is a dose level below which no observable effect occurs.

Thresholds are thought to exist for certain effects, like acute toxic effects; but

not for others, like carcinogenic effects (by DNA-adduct-forming initiators). The

mere absence of a response in a given population should not, however, be taken

as evidence for the existence of a threshold. Absence of response could be due to

simple statistical phenomena: an adverse effect occurring at low frequency may not

be detectable in a small population.

LD50 (lethal dose) is the dose causing 50% lethality in an animal population.

The

is often given in older literature as a measure of acute toxicity of

chemicals. The higher the

, the lower is the acute toxicity. A highly toxic

chemical (with a low

) is said to be potent. There is no necessary correlation

between acute and chronic toxicity.

ED50 (effective dose) is the dose causing a specific effect other than lethality

in 50% of the animals.

Chemical accident is breakdown of technological process, damage

of pipelines, tanks, reservoirs, transport facilities that causes ejection into

environment of strong toxic substances.

Zone of chemical pollution includes spot (I) of ejected chemical agents and

territory polluted with their vapor cloud (II) (fig. 9).

Fig. 9 Zone of chemical pollution

Alarm signal about chemical accident “Attention!”, sirens or interrupting

horn sound and also instructions about how to protect houses, food and water are

broadcasted via loudspeakers.

If you hear that sound, turn on TV and Radio to get more information

about accident and instruction how to behave. Shut the windows, shut down

electricity and turn off the gas. Put on rubber boots, coat, take documents, wear,

3-day storable food, inform your neighbors and quickly leave the house. Leave

possible zone of chemical pollution moving perpendicular to wind. Go the distance

about 1.5 km from your current position. To protect respiratory organs wear anti-

gas, filter mask, or just wet fabric. It’s recommended to wet fabric with 2-5%

baking soda mixture to protect against the chlorine or 2% lemon or acetic acid to

protect against ammonia. If you can’t leave polluted zone, shut the doors, widows,

ventilation and chimney tight. Seal the gaps in them with scotch or paper. Don’t

hide in basements or at the first floor. If you suspect chemical poisoning try to

avoid physical exertion, drink much milk, tea and immediately go to doctor.

34. NATURAL EMERGENCY SITUATIONS

Here the characteristic for some natural catastrophes is given.

The earthquake is the force shacking of the earth's crust induced by tectonic

or volcanic cause that results in ruin of structures, fires and people victims.

Main earthquake characteristics are size of hit site, magnitude, intensity

of energy on the earth surface. Earthquake’s size of hit site can be of 10..30 km,

sometimes it is much more.

Magnitude characterizes general energy of earthquake and represents a

common logarithm of ratio of maximum ground oscillation amplitude measured

in the investigated place by seismograph in microns to maximum amplitude of

ground oscillation defined on the distance of 100 km from the epicenter.

Magnitude (M) by Richter scale is measured from 0 up to 9 (last number

corresponds to the most powerful earthquake).

The intensity of energy on the surface of the ground is measured in numbers.

It depends on hit site size, magnitude, distance from epicenter, geological structure

of the ground. For earthquake energy intensity measurement in our country 12-

numbers Richter scale is accepted.

Table 5

Magnitude by

Richter scale

Earthquake characteristic

World annual

Earthquake

average rate of

duration, sec

earthquakes

1

30..90

15

20..50

140

10..30

900

2..15

8000

0..5

Radius of hit site, km

80..160

50..120

20..80

5..30

0..15

The earthquakes bring large material losses and kill thousands people. For

example, on June 21,1990 during earthquake having intensity of 8 numbers by the

Richter scale at northern Ural in the province of Shlyan more than 50,000 people

perished and about 1,000,000 people were injured and left out of living places.

Table 6

The largest earthquakes of XX century

Year

Place

Victims

(thousands)

1920

Ganyasu (China)

180

1923

Fokto (Japan)

over 100

1960

Agadir (Morocco)

12

1970

Chimbote (Peru)

66

1976

Tanshan (China)

243

1978

Iran

15

1988

Armenia

25

Protection from earthquakes implies beforehand detecting of seismic

dangerous zones in various regions of country, that is seismic zoning. On maps

of seismic zones where earthquakes of intensity above 7..8 numbers by Richter

scale are possible are marked. In such regions they carry out various protective

measures, chemical factories and nuclear power stations are not admitted to build

in.

Flood is a significant water filling of district after increasing of water

level in river, lake caused by various reasons (rain, ice jam on the rivers, dam

destruction and other). Floods result in material losses and human victims.

At the beginning of July, 1990 heavy showers in Zabaykallia caused the

flood which destroyed 400 bridges and brought the losses of 400,000,000 in

national currency. Thousands people remained without living place or perished.

Floods can cause fires as the result of short-circuit of power cable, and also

destruction of pipes, electrical, television and telegraphic networks.

The main direction in flood struggle is decreasing of maximum water gain in

a river by the redistribution of the flow in time (preservation of plants near water,

planting of forest shelter belts etc). For the protection from flood the system of

dams is used.

Land-slide is shifting of mountain masses down the slope, that appears

because of equilibrium breaking caused by many reasons (ground undermining,

unreasonable economic activity etc).

Land-slides can take place in all hills with slope 200 and more in any

season. They differ both in speed of mass moving (slow, middle and fast), and in

scale. The slow slides speed makes tens centimeters per one year, middle - some

meters per hour or 24 hours, fast - tens kilometers per hour and even more. Only

fast slides can get the cause of catastrophes with people victims. For example,

in 1911 in the Pamirs the powerful earthquake induced large land-slide. Near

2,500,000,000 m3 of loose masses moved down. Village Usoi with 54 residents

was dumped. The land-slide has parted off the valley of the river Murgay and

created the dump lake which has flooded the village of Saraz. The height of that

natural dam reached 300 m, depth of the lake - 284 m and length - 53 km.

Precaution measures are transformation of ground relief, fixing of a slope by

piles, construction of supports.

Snow avalanches are also referred to land-slides and appear as sliding

displacements. Gravity makes displacement of snow masses down the slope. Snow

avalanche is a compound of snow crystals and air. Large avalanches arise on

25..600 slopes. For example, on July 13, 1990 in the Pamirs the earthquake and

snow avalanche demolished camp of the climbers, which was located on the height

of 5300 m, 40 men perished.

The protection from avalanches can be passive and active. In passive

protection protecting shields are applied. In active protection avalanche-dangerous

slopes shooting is carried out.

Mudflow is a flood with a very large concentration of mineral particles,

stones, fragments of mountain rock (what makes from 10..15 up to 75 % of total

flow volume), which occurs in pools of small mountain rivers and is caused by

rain, sometimes by intensive snow thawing. Danger of mudflow consists not only