Yeung Chihung

1
Yeung Chi-hung ??? Office Rm. GH639 Tel.
27665624 E-mail bcchye_at_polyu.edu.hk
2
Hazardous Properties of Chemicals
Explosive
Flammable
Auto-ignited
Ignite when in contact with water
Supporter of burning / Oxidiser
Corrosive
Irritating
Poisonous
Toxic
Harmful
Radioactive
Suffocating
3
Explosive Substance
Explosion
Some substances, when triggered by
other substances or by external forces such as
heating, grinding or impact, may react violently
in a very short time interval, producing a lot of
gases and heat. The rapid expansion of the gases
produces shock waves and a loud noise.
4
Characteristics of Explosive substances
Extremely fast rate of reaction
A lot of heat is produced in the course of
reaction
The reaction produces a large amount of gaseous
product
5
Chemical Nature of Explosive Substances
(1) Single component
e.g. Trinitrotoluene (TNT)
Ammonium nitrate
(2) Fuel Oxidant
e.g. Black powder ( a mixture of charcoal,
sulphur and
sodium nitrate)
6
Special precautions for storage
Sensitivity
Chemical structure (substances with both
oxidising and
reducing functional groups
are potentially explosive)
Temperature
Impurity (small amount of impurity may induce
explosive decomposition e.g.
hydrogen peroxide)
Instability
Induced explosion
7
Flammable Substance
The 3 elements for burning
Fuel
Oxidant
Temperature
A fire can start or sustain if and only if
all the 3 basic elements are present.
Burning is a gas phase reaction, the reactants
have to be vaporized before the reaction can take
place temperature cannot be too low.
8
Flash Point
It is the minimum temperature at which a
substance, contained in a specified container,
produces enough vapor to be ignited by an
external source of ignition.
A substance is more easily ignited if it is
having a lower flash point.
Auto-ignition Temperature
It is the minimum temperature at which a
substance ignite spontaneously in air without any
external source of ignition.
9
Explosive Limit
A mixture of air and combustible substance of
suitable proportion can burn at a extremely fast
rate when ignited.
The heat of burning will cause rapid expansion of
the gaseous products resulting in a rapid build
up of pressure which leads to an explosion.
Upper and Lower Explosive Limits
The maximum and minimum concentration of
combustible substance in a potentially explosive
mixture.
A substance is more hazardous if it is having a
wide explosive limit.
Combustible substances are dispersed in the
explosive mixture in the form of vapour or
small particles.
10
Spontaneously Combustible Material
An extremely reactive substance may be ignited
spontaneouly by the heat of reaction produced by
the oxidation reaction between air and the
surface of the substances.
This substance may also be ignited if its
temperature reaches the auto-ignition temperature.
11
Material Ignited by Interaction with Water
Any substance that can react violently with water
to give combustible gas(es) and heat. The heat
produced can then ignite the combustible gas(es).
e.g. alkali metals, calcium carbide (calcium
acetylide)
12
Supporter of Burning / Oxidizing Agent
These substances do not burn but they can
decompose easily to give oxygen or other oxidant.
13
Compressed / Liquefied Gas
Compressed gas
Gases are usually stored under pressure within
strong containers
Liquefied gas
Some gases will liquefy when compressed, e.g.
chlorine
Some other gases are liquefied by cooling, e.g.
nitrogen
14
Hazardous Nature of Compressed / Liquefied Gas
Explosion
Explosion may be caused by the rupture of
container, fittings or connecting tubings. These
ruptures may be caused by material fatigue or
excessive internal pressure. The energy released
by the instantaneous expansion of high
pressure gases is enormous.
15
Hazardous Nature of Compressed / Liquefied Gas
Suffocation
Escaped gases may dilute the oxygen content of
air and cause suffocation. e.g. carbon dioxide,
nitrogen, hydrogen
Toxicity
e.g. chlorine, ammonia
Flammability
e.g. ethyne (acetylene), hydrogen
Supporter of burning
e.g. oxygen, nitrous oxide
16
Poisonous Substance
Substances that cause temporary or permanent
damages to body tissue or body functions if they
are in contact with the skin or enter the body
in small quantities.
These substances may even cause death.
17
Lethal Dosage LD50
The minimum dosage that causes the death of half
of the total number of test animals within a
prescribed period.
The dosage is expressed as mass of chemical per
kilogram body weight
18
Threshold Limit Value, TLV
Airborne concentration of a substance to which an
averageperson can be exposed without adverse
health effects.
These are exposure guidelines devised by American
Conferenceof Government Industrial Hygienist,
ACGIH.
TWA Time Weighted Average Usually determined
for a 8 hours working day, 5 days per week.
STEL Short Term Exposure Limit (15 minutes)
C Ceiling
19
Permissible Exposure Limit, PEL
An exposure limit published and enforced by
OccupationalHealth and Safety Administration,
OSHA of USA
TWA
STEL
C
20
Harmful Substances
Substances that are less harmful than poisonous
substances
21
Corrosive Substances
Substances that cause corrosion to our body or
other material.
Corrosive substances can burn body tissues and
can cause serious consequences if they are
ingested or come into contact with internal
organs.
22
Irritant
Substances that irritate body tissues causing
pain, itching or swelling of the tissue.
23
Radioactive Substances
Radioactive substances will emit invisible,
penetrating radiation or particles. These
radiation and particles can cause burns and
damages to body tissues and interfere with normal
cell growth.
Harmful effects of radioactive substances are
more severe if they enter our body.
24
Physiological Damages caused by Chemicals
1. Chemical burns
2. Irritations to skin Dermatisis
3. Poisoning
25
Biological Effect of Harmful Chemicals
1. Irritating
2. Corrosive
3. Suffocating
4. Anaesthetic
5. Haemolytic
6. Sensitising
7. Carcinogenic
8. Mutation inducing
9. Inducing abnormal embryo
26
Classification of Harmful Substances (according
to nature and action)
(1) Irritant
(2) Suffocating substances
(3) Anaesthetic substances
(4) Inorganic compounds and organometallics
27
State of Harmful Substances
(1) Vapour/Gas
(2) Dust (solid particles)
(3) Mist (liquid droplets)
28
Routes of Entry of Harmful Substances into Our
Body
(1) Mouth Gastro-intestinal tract
(2) Respiratory tract Lung
(3) Skin Absorption
(4) Wounds
29
Toxicity Indicators of Toxins
(1) Lethal Dosage / Concentration total death
(LD100 or LC100)
(2) Lethal Dosage / Concentration 50 death (LD50
or LC50)
(3) Minimum Lethal Dosage / Concentration (MLD or
MLC)
(4) Highest Tolerable Dosage / Concentration (LD0
or LC0)
(5) Threshold Limit Dosage / Concentration (TLD
or TLC)
(a) Acute
(b) Chronic
30
(No Transcript)
31
Concentration Units
(a) for air-borne toxins
mg/m3, g/m3, mg/L, ppm (parts per million)
ppm mg/m3 24.45 / relative molar mass of toxin
mg/m3 ppm relative molar mass of toxin / 24.45
at STP, the molar volume of a gas is 24.45 L
mole-1
(b) for toxins in solution
mg/m3, g/m3, mg/L, ppm, w/v, v/v
32
Personal Protection against Harmful Substances
(1) Good working habits
(a) No eating and drinking in workplace
(b) Frequent hand-washes
(c) Take off overcoat / protective clothing when
leaving workplace
(d) Dress wounds with water-proof dressings
33
Threshold Level Time-weighted average pollutant
concentration values, exposure beyond which is
likely to adversely affect human health. (See
environmental exposure)
Threshold Limit Value (TLV) The concentration of
an airborne substance to which an average person
can be repeatedly exposed without adverse
effects.
34

• TLVs may be expressed in three ways
• TLV-TWA Time weighted average, based on an
  allowable exposure averaged over a normal 8-hour
  workday or 40-hour work- week
• TLV-STEL Short-term exposure limit or maximum
  concentration for a brief specified period of
  time, depending on a specific chemical (TWA must
  still be met) and
• TLV-C Ceiling Exposure Limit or maximum
  exposure concentration not to be exceeded under
  any circumstances. TWA must still be met.)

35
Personal Protection against Harmful Substances
(1) Good working habits
(a) No eating and drinking in workplace
(b) Frequent hand-washes
(c) Take off overcoat / protective clothing when
leaving workplace
(d) Frequent washing / changing of protective
clothing
(e) Dress wounds with water-proof dressings
36
Eye Protection
Protection should be provided for splashes from
the front, the side, from above and below.
Type of protection depends on level of risk
If there is high risk of explosion, use
protective shields
37
(No Transcript)
38
(No Transcript)
39
Personal Protection against Harmful Substances
(2) Personal protection gear
(a) Respiratory protection
(i) Simple filters
Useful only for harmless and large particles
(ii) Absorptive filters
Different chemicals may require different
absorbents
Useful only in low concentration environment
Absorbents will be saturated by high
concentration or prolonged use
(iii) Self-supplying respirator
Relatively superior but requires training in use
40
(No Transcript)
41
(No Transcript)
42
Personal Protection against Harmful Substances
(2) Personal protection gear
(b) Protection for skin contact
Gloves
Protective clothing
Face shield
Helmet
The material and construction should be of the
correct type
43
(No Transcript)
44
(No Transcript)
45
Confining the Chemicals
Glove Box
Fume-hood
46
Glove Selection Guide
(1) Nature of chemical and exposure time
(2) Chemical hazards
(3) Material for best protection
(4) Proper fit
47
Common material for gloves
Latex
Natural rubber
Polyethylene
Polyvinyl chloride
Butyl rubber
Polyvinyl alcohol
Telfon (polytetrafluoroethylene)
Fluorinated rubber (Viton)
Nitrile rubber
48
(No Transcript)
49
Emergency plan
Organizations dealing with chemicals or chemical
wastes should have emergency plan to deal deal
with emergent cases of spillage or leakage of
chemicals or chemical wastes
Emergency Control Team
Team members should consist of people from all
rank
The team should be well trained
The team should have the support of the senior
mangement
50
Safety Audit
Regular inspection for safety
Inspection team should consist of team members
from all rank
There should be a pre-approved audit form
All audit reports should be reviewed and recorded