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Pressure Hazards at Workplace
Lecture 20
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Definition
Pressure is force acting on a unit area (Force/Area)
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Units of pressure
1 atmosphere equals to:
= 29.9 inches (760 mm) of Hg
= 33 feet (10.08 meters) of seawater
= 101.3 kilopascals (kPa)
= 14.7 pounds per sq inch (psi)
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Composition of Gases in Atmosphere
Component Symbol Volume Percent
Nitrogen N 78.094
Oxygen O 20.948
Argon A 0.934
Neon Ne 0.001818
Helium He 0.000524
Hydrogen H 0.00005
Others (Co, Kr, Xe etc) 0.01
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Gas Laws
1. Boyles Law: Volume of gas is inversely proportional to its pressure in body (PV=K) .
P1V1-P2V2. (Trapped gas in cavities)
2. Daltons Law: Total pressure of mixture of gases equals sum of partial pressure of each gas in
mixture. PT=P1 + P2 +Pn (Hypoxia)
3. Gaseous diffusion: Gas will diffuse from area of
high concentration to area of low concentration
(Transfer of gases in body (O2 and CO2).
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TYPES OF PRESSURE HAZARDS
1. HYPERBARIC
2. HYPOBARIC
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1. HYPERBARIC WORK ENVIRONMENT
(below sea level pressure or aquatic)
Potential hazards:
1. Mechanical effects
2. Inert gas narcosis
3. Effects of CO2 accumulation
4. Oxygen toxicity
5. Decompression sickness
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Body cavities trapped with gases
1. Lungs
2. Middle ear
3. Sinuses
4. Tooth cavities
5. Stomach
6. Intestines
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Boyles Law and Diving
Air 760 mm Hg 14.7 psi 1 at
Sea 33 ft 1520 mm Hg 29.4 psi 2 ats
Sea 66 ft 2280 mm Hg 2280 mm Hg 3 ats
Sea 99 ft 3040 mm Hg 58.8 psi 4 ats
Sea 132 ft 3800 mm Hg 73.5 psi 5 ats
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Decompression sickness (Caisson Disease)
Effect due to air bubbles in the tissue and blood vessel.
Nitrogen gas air bubbles is the commonest.
Rapid ascension 9 m depth. Or sudden pressure loss at attitude > 7000m
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Types of decompression Sickness (1-3)
Type 1 Affect limbs and skin; Acute pain at major joints; Pain immediate 12 hrs after decompression; Good prognosis.
Type 2 Type 3
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Types of decompression Sickness (2-3)
Type 2: Symptom central-peripheral nerves damage
Paralysis, weakness of limbs, headache seizures, visual defects etc.
Pulmonary barotrauma
Tissue infarction
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Types of decompression Sickness (3-3)
Type 3: Chronic/ long term effect,
Osteonecrosis
Memory deficit
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1. Bends joint pains 74%
2. Creeps skin rash 7%
3. Chokes chest discomfort 5%
4. Staggers neurological complaints 1%
5. Visual disturbances 2%
6. Reduced of awareness/ confusion 9%
Manifestations of Decompression sickness 28000 feet Altitude
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1. Ill health
2. Old age
3. Obesity
4. Exercise/ exertion
5. Drugs
6. Alcohol
7. Cold
8. Hypoxia
9. Previous exposure to decompression, e.g. several
unpressurized flights scuba or professional diving before
flight
Factors predisposing to Decompression Sickness
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2. HYPOBARIC WORK ENVIRONMENT
(Low pressure (above sea level) aviation, space industry)
Potential hazards:
1. Reduction in partial pressure of oxygen
2. Decompression
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Ambient air partial pressure (mmHg)
Alveolar air partial pressure (mmHg)
Nitrogen 600 570
Oxygen 160 103
Carbon dioxide 40
Water vapour 47
TOTAL 760 760
Daltons Law and Hypoxia
% saturation of hemoglobin varies with changes in partial pressure of alveolar oxygen at various altitudes
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1. Feeling tiredness, sleepiness
2. Euphoria with outbursts of joy
3. Impairment of judgment
4. Dulling of thoughts
5. Light headedness, dizziness, nausea
6. Tingling of hands and feet
7. Pallor of skin, cyanosis
8. In-coordination of limbs and disorientation
9. Failing of vision
10. Semi-consciousness
11. Unconsciousness
Effects of Increasing Hypoxia to Central Nervous System
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Time of Useful Consciousness with Increasing Altitude
Rapid disconnect of O2 Systems
Altitude (ft) Moderate activity Sitting activity
22,000 5min 10min
25,000 2min 3min
30,000 45s 1 min
35,000 30s 45s
40,000 18s 30s
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Rapid disconnect of O2 Systems
Altitude (ft) Moderate activity Sitting activity
22,000 5min 10min
25,000 2min 3min
30,000 45s 1 min
35,000 30s 45s
40,000 18s 30s
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Hyperbaric Chamber
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1. Advice on health effects of pressure changes;
2. Treatment of pressure related complications;
3. Medical selection of workers to be engaged in
work in hypobaric or hyperbaric environments;
4. Periodic medical examination of diving or
aviation personnel;
5. Certification of invalidity for air travel.
Role of occupational health doctor
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