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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