Inert gas – fades burning;

sand – effective to extinguish oil substances, absorb heat and replace

oxygen;

covering materials – clothing, ground.

Fire fighting means are classified as:

primary;

fire alarm;

fire machines;

automatic fire fighting units.

Extinguishers types:

- chemical foam: operation time 60 sec, stream distance 6-8 m, can’t be used

to extinguish electric facilities;

- carbon dioxide: operation time 20-60 sec, stream distance 2 m, looks like

snow mass at temperature -79 deg C;

- powder: operation time 10-30 sec, stream distance 5 m.

Personal fire fighting rules include the steps which should be taken in such

priority:

1. call 01;

2. engage fighting fire;

3. evacuate people and property;

4. inform the higher-up staff;

5. leave the area through main or safe exits;

6. shut the door tight;

Personal safety rules in fire zone:

- breath through wet fabric;

- stay clone;

- stay near the walls.

30. THEORY OF BURNING

Burning is chemical process in which a substance reacts with oxygen to

produce a significant rise in temperature and the emission of light.

Key components for burning:

- flammable substance;

- oxidant (normally oxygen in air);

- igniter (impulse for ignition).

Types of burning by speed of fire spreading:

- deflagration – burning that spreads fire with the speed of dozens meters per

second;

- explosion – hundred meters per second;

- detonation – thousands meters per second.

Types of processes that initiate burning:

flash – rapid burning of inflammable mixture which is not followed with the

flame;

ignition – the act or process of initiating burning from igniter;

self-ignition – thermal initiating burning without igniter;

explosion – a violent release of energy resulting from a rapid chemical

reaction, esp. one that produces a shock wave, loud noise, heat, and light.

31. FIRE AND EXPLOSION RISK INDEXES

I. Self-ignition point: the lowest temperature of a substance that causes self-

ignition.

II. Concentration limits of ignition: lower and upper ones.

The lowest concentration of flammable gas or vapor at which it can already

be ignited is called lower limit of ignition.

The highest concentration of flammable gas or vapor at which it can still be

ignited is called upper limit of ignition.

III. Flashpoint: the lowest temperature of a substance that causes flash.

Using flash point flammable liquids are divided into two classes:

- high-inflammable: those with the flash point lower or equal 61 deg C, such

as gasoline, spirit, acetone;

- inflammable: those with the flash point over 61 deg C, such as oil, black oil.

IV. Ignition point: the lowest temperature of the substance that causes

ignition.

V. Temperature limits of ignition: temperatures corresponding to

concentration limits.

VI. Flammability group:

- inflammable (flammable): liable to catch fire;

- hard-inflammable: liable to catch fire only in presence of igniter;

- nonflammable: unable to catch fire.

The indexes applicability for certain substance (table 4) depends on what

aggregation state it has: liquid, gaseous, solid or dust.

Table 4

Applicability of fire-explosive indexes

Index

Fire-explosive indexes application for

gas

liquid

solid

dust

Flammability group

+

+

+

+

Flash point

-

+

-

-

Ignition point

-

+

+

+

Self- ignition point

+

+

+

+

Lower (upper) concentration limits of

+

+

-

-

ignition

Temperature limits of ignition

-

+

-

-

32. FIRE AND EXPLOSION RISK AREA CATEGORIES

In reference to standard «SNIP 24-86» all work areas are divided into 5

categories: «A», «Б», «В», «Г», «Д».

Work area is relevant to some category dependently on characteristics of

substances stored or used in the area (table 5).

Table 5

Fire and explosion risk area categories

Area Category

Characteristics of materials and substances stored in the area

1

2

«A»

Inflammable substances with:

fire and explosion lower limit of ignition 10% or lower;

risk area

flashpoint lower or equal 28 deg C;

in condition that mentioned substances can make explosive

mixtures in volume covering 5 % of the total area volume.

Such as: painting workshops, areas storing pressured gas.

Б

Inflammable substances with:

fire and explosion lower limit of ignition over 10%;

risk area

flashpoint over 28 to 61 deg C;

in condition that mentioned substances can make explosive

mixtures in volume covering 5 % of the total area volume.

Such as: areas using ammonia, and emitting flammable dusts.

«B»

Inflammable substances with:

fire risk area

flashpoint over 61 deg C;

solid flammable substances liable only to catch fire but not

explosion.

Nonflammable substances in hot, molten and red-hot

condition;

And also substances which are burned as fuel.

Areas using nonflammable substances in cold condition.

The importance of accurate defining Category of fire-explosive risk for an

area or a building is extremely high because the considered Category significantly

defines requirements to building’s construction and floor plan, organization of fire

safety and its technical equipment.

32. NUCLEAR ACCIDENT

Nuclear blast hazards:

Shockwave

Fireball

Penetrating radiation

Radiation pollution

The nuclear blast hit site margin is assumed the imaginary line at the

landscape in which superatmospheric pressure in front of the shockwave ∆Pf = 10

kPa. Such pressure is supposed to be safe.

Shockwave is a region across which there is a rapid pressure, temperature,

and density rise caused by a body moving supersonically in a gas or by a

detonation.

To assign necessary rescue and assistance forces nuclear blast hit site is

conventionally divided into 4 areas.

Damage zones (fig. 7):

1. fatal damage (radius R1): fatality rate – 90%; fatal damage of buildings and

power supply systems; 25% damage of emergency shelter;

2. major damage (radius R2): fatality rate – 50%; fatal damage of civil

buildings, and major damage of industrial buildings;

3. medium damage (radius R3): fatality rate – 40%; major and minor damage of

civil buildings;

4. minor damage (radius R4): fatality rate – 15%; minor and negligible damage

of civil buildings.

Fig. 7 Damage zones in nuclear hit site

Fireball appears in the moment of blast and consists of hot products of the

blast and air. Light flash (I) is brief bright light emitted by blast and defined as

luminous intensity: the average time rate of flow of light through perpendicular

area. Measuring units are kJ/m2.

3

Light flash duration t = q (sec), where q – blast power measured in kilo

Burns caused by light flash are classified as:

first-degree burn: skin surface painful and red; I = 100-200 kJ/m2;

second-degree burn: blisters appear on the skin; I = 200-400 kJ/m2;

third-degree burn: destruction of both epidermis and dermis I = 400-600 kJ/m2;

fourth-degree burn: chair; I > 600 kJ/m2.

Eyes affection:

- temporary blinding may last for 30 min;

- burn of fundus of the eye caused by staring at fireball even from the safe

distance;

- burns of cornea and eyelid occur at the same distances as skin burns.

Fire site is divided into 3 zones:

1. overwhelms fire zone: smoldering hazard (burning slowly without flame,

usually emitting smoke) survivals and rescue unit are exposured to;

2. extensive fire zone: about 50% buildings on fire, after 2 hours fire spreads to

the rest;

3. several fire zone: only several buildings are on fire.

Radius of fire zone:

Radiation exposure is the emission or transfer of radiant energy emitted in

nuclear blast only within 10-15 sec.

Read more detailed information about radiation exposure in points 20, 21.

Radiation pollution usually has shape of the ellipse, which spreads in wind

direction covering part of hit site and great territory out of hit site (fig. 8).

R = K3 q

, where K – factor which depends on blast

Fig. 8 Radiation contamination

Depending on radiation level the contaminated territory is broken into 4

zones:

1. A zone of minor pollution;

2. B zone of strong pollution;

3. C zone of dangerous pollution;

4. D zone of extremely dangerous pollution.

In zones’ margins radiation levels at first hour after blast are: 8 (A), 80 (B),

240 (C), 800 (D) Rph.

Radiation decay lowers radiation level in time. Radiation level time rate is

expressed by formula:

Рt = Р1 ⋅ Кt = Р1 ⋅ t-1,2

(14)

where Рt – current radiation level at some time; Р1 – first hour radiation level; Кt -

time rate factor; t – time, which passed after blast.

In zone A: exposure dose till full radioactive decay makes from 40 to

400 R at external and internal margins correspondently. People have to stay in

radiation protective shelters no longer than 24 hrs. After what they may leave

shelters for dwellings. During next 24 hrs they may go outside only for 4 hrs. It’s

recommended to wear protective clothing in windy and dry weather.

In zone B: exposure dose till full radioactive decay makes from 400 to 1200

R at external and internal margins correspondently. People have to stay in radiation

protective shelters from 1 to 3 days. Then they are strongly recommended to stay

inside their houses at least for next 4 days. To leave house is allowed only for 3-4

hrs a day and wearing protective clothing.

In zone C: exposure dose till full radioactive decay exceeds 1200 R. People

have to stay in radiation protective shelters 3 days or longer. Then they are strongly

recommended to stay inside their houses at least for next 4 days. To leave house is

allowed only for 3-4 hrs a day and wearing protective clothing.

If there was no radio transmission about how long to stay in the shelter

people have to follow instructions given for zone C. Evacuation from zone C is

possible only 3 day later radiation pollution.

Only food kept in air-tight wrap, refrigerator, or cellar is clear from

radioactive substances. However before use the wrap should be cleaned with

washer. Radioactive substances penetrate into food at different depth; the deepest

layer which can be polluted makes about 3 cm. To deactivate polluted food one

should remove upper unguarded and hence polluted layer. Water is potable only

from central water-supply system.

Radiation dose that people can get during their stay in the open

territory polluted with radioactive substances is expressed by formula:

Dopen = Pmean ⋅ Т,

(15)

where Pmean - average radiation level within exposure time; T – duration

of exposure (that long people stayed in the polluted territory and were

exposed to radiation).

If people stayed in radiation protective shelters, houses or transport

radiation dose should be found with consideration of protection effect.

Protection effect is evaluated with reduction coefficient, which can be

calculated by formula:

K red = 2

h

d

,

(16)

where h – thickness of protective material (walls, roofs); d – width of the

half reducing radiation layer (thickness of the wall that twice reduces

external level of radiation).

Half reducing radiation layer is expressed by formula:

23

d =

ρ ,

(17)

where ρ - density of protective material (gm/cm3).

Reduction coefficient of multilayer shelters is found by multiplying

coefficients of every protective layer:

K red = 2

h1

h2

+

+ ...

d1

d2

(18)

Radiation dose that people can get during their stay in radiation

protective shelter is calculated by formula:

.

Dopen

D RPS =

К red

.

(19)

Normally people can visit various places during the day, thus total

radiation dose is the sum of many doses:

Dtotal=D1 + D2 + D3 + ... + Dn.

(20)

Problem:

After nuclear accident territory was polluted with radioactive

substances, pollution occurred at 1 hour after the accident, radiation level

at first hour after the blast was P1 = 200 rad/hrs.

Find radiation dose and possible fatality if right after accident people

stayed in the shelter during T1 = 4 hrs and then worked at the open territory

for another T2 = 12 hrs. The shelter is two-layer construction made form

concrete and brick. Concrete (ρ1 = 2.3) layer makes 20 cm, brick (ρ2 = 1.6)

layer makes 115 cm.