Describe the occupational hazards due to physical and chemical agents.

Physical Agents

• Heat — affecting foundry, glass, mining, steel, brick kiln, agricultural and construction workers
• The disorders form a graded series — heat cramps from salt loss; heat exhaustion with weakness, headache, nausea, sweating and hypotension but a preserved mental state; and heat stroke, in which thermoregulation fails
• Heat stroke is distinguished by altered mental state and a core temperature above about 40°C, classically with hot dry skin because sweating has ceased — and is a medical emergency requiring immediate cooling
• The presence or absence of sweating is the clinical discriminator, and the treatment of heat stroke is cooling first, before anything else
• Also — heat syncope, prickly heat and, increasingly recognised, chronic kidney disease of unknown aetiology in agricultural workers exposed to repeated heat stress and dehydration
• Prevention — acclimatisation over days; adequate water and salt; work-rest cycles and rescheduling to cooler hours; shade, ventilation and cooling; screening of the heat intolerant; and heat action plans
• Cold — frostbite, chilblains, trench foot and hypothermia, in cold storage workers, fishermen and those at high altitude
• Vibration divides into two entirely different problems:
• Hand-arm vibration from pneumatic drills, chain saws, grinders and polishers, causing vibration white finger (secondary Raynaud phenomenon), with episodic blanching of the fingers on cold exposure, together with sensory loss, reduced grip and, in severe cases, bone and joint changes
• Whole-body vibration from tractors, trucks and heavy earth-moving equipment, causing low back pain and spinal degeneration
• Abnormal pressure — affecting divers, caisson and tunnel workers
• Decompression sickness (caisson disease, "the bends") arises when nitrogen dissolved in tissues under pressure comes out of solution as bubbles during too rapid decompression
• Its features — joint and limb pain (the bends); itching and skin marbling; respiratory distress (the chokes); and neurological features including paraplegia
• The late complication is aseptic (avascular) necrosis of bone, particularly the head of the femur and humerus
• Prevention is entirely a matter of slow, staged decompression according to tables, with limits on depth and duration and medical fitness examination; and treatment is recompression in a chamber followed by controlled decompression
• Noise, lighting and radiation are considered in the environmental health chapter; the occupational aspects are audiometric surveillance, the 4000 Hz dip, hearing conservation programmes, and personal dosimetry

Chemical Agents

• The routes of entry — inhalation, which is much the most important; skin absorption, which is greatly underestimated and is why air monitoring alone can mislead; and ingestion, chiefly from contaminated hands, food and smoking at the workplace
• The practical rule that follows — NO eating, drinking or smoking in the work area, and washing before meals, which prevents the ingestion route entirely
• Lead is the classic occupational poison and should be described in detail
• Its occupations — battery manufacture and recycling, which is the largest source in India; painting and paint removal; printing; smelting; welding and cutting of painted metal; ceramic glazing; and lead pipe work
• Its clinical features — abdominal colic with constipation; anaemia, which is microcytic with basophilic stippling of red cells; peripheral neuropathy, classically wrist drop or foot drop affecting extensors; encephalopathy, particularly in children; a blue-grey lead line on the gums (Burton line); renal impairment; and reduced fertility and adverse pregnancy outcome
• IN children the effect that matters most is cognitive — lead lowers IQ, and there is NO known safe blood level
• Diagnosis — blood lead is the standard test; with urinary delta-aminolaevulinic acid and blood zinc protoporphyrin as supporting evidence of effect
• Management — removal from exposure, which is the essential step; and chelation with calcium disodium EDTA, dimercaprol, penicillamine or succimer for significant poisoning
• The critical point about chelation — it is useless if exposure continues, and treating a worker and returning them to the same job is futile
• Mercury — in chlor-alkali plants, thermometer and instrument manufacture, dentistry and gold extraction
• Chronic exposure causes the classical triad of gingivitis with excessive salivation, tremor (intention tremor beginning in the fingers, eyelids and tongue) and erethism — a change in personality with irritability, shyness, loss of confidence and insomnia
• The term "mad as a hatter" derives from mercury use in felt hat making, which is worth knowing as the origin of the phrase
• Also — renal damage; and, for organic (methyl) mercury, the minamata disease pattern of ataxia, constricted visual fields, deafness and severe fetal damage
• Cadmium — causing emphysema, renal tubular damage with proteinuria, and osteomalacia (itai-itai disease)
• Arsenic — peripheral neuropathy, hyperkeratosis and pigmentation of the palms and soles, and skin, lung and bladder cancer
• Manganese — causing a parkinsonian syndrome and psychiatric disturbance
• Chromium and nickel — dermatitis, nasal septal ulceration and perforation, and lung and nasal cancer
• Solvents — benzene causing aplastic anaemia and leukaemia; toluene and xylene causing narcosis and neurotoxicity; carbon tetrachloride causing hepatotoxicity; and trichloroethylene
• Gases — carbon monoxide; hydrogen sulphide, dangerous because it paralyses the sense of smell at high concentration, so the warning disappears exactly when the danger is greatest; ammonia and chlorine; and methyl isocyanate, the agent of the BHOPAL disaster of 1984
• BHOPAL should be named as the world’s worst industrial disaster, and its lessons stated — siting of hazardous industry near dense population; inadequate safety systems and maintenance; absence of community awareness and any emergency plan; the unpreparedness of local health services, who did not know what agent they were treating or what antidote to give; and the long, unresolved question of compensation and long-term health surveillance
• Pesticides — considered with agricultural hazards
• Occupational dermatoses form the largest group of occupational disease by number, mostly irritant contact dermatitis, with a smaller proportion allergic, caused by detergents, solvents, cement (chromate), rubber, oils and wet work
• The distinction matters — irritant dermatitis improves with reduced exposure and better protection, while allergic dermatitis requires complete avoidance once sensitisation has occurred
• Chelation is useless if exposure continues, so removal from exposure is the treatment and the drug an adjunct
• Hot dry skin with confusion is heat stroke, since sweating has failed, and cooling comes before everything else
• Hydrogen sulphide abolishes the sense of smell exactly when the concentration becomes lethal, which removes the warning
• Skin absorption is greatly underestimated, which is why air monitoring alone can mislead about total dose
• No eating, drinking or smoking in the work area, which closes the ingestion route entirely and costs nothing
• Wrist drop is the classical lead neuropathy, affecting extensors, alongside colic, anaemia and basophilic stippling
• There is no safe blood lead in children, whose cognitive loss is the effect that matters most
• Battery recycling is the main Indian lead source, much of it in the unorganised sector and entirely unmonitored
• Mercury gives gingivitis, tremor and erethism, which is the classical triad and the origin of mad as a hatter
• Manganese causes a parkinsonian syndrome, which is easily attributed to idiopathic disease if no history is taken
• Benzene causes aplastic anaemia and leukaemia, which is why toluene substitution was such an important change
• Decompression sickness is prevented by slow ascent, and treated by recompression followed by controlled decompression
• Avascular necrosis is the late caisson complication, affecting the femoral and humeral heads years afterwards
• Vibration white finger follows hand-arm exposure while whole-body vibration causes low back pain
• Acclimatise workers over several days, which substantially reduces heat illness and is frequently skipped
• Heat stress may cause chronic kidney disease in agricultural workers, which is an increasingly recognised association
• Irritant dermatitis improves with less exposure while allergic dermatitis requires complete avoidance
• Dermatoses are the largest occupational group by number, though they attract the least attention
• Bhopal was the worst industrial disaster, and its lessons concern siting, safety systems, community awareness and preparedness
• Local health services did not know the antidote at Bhopal, which is the lesson most directly relevant to a clinician
• Cadmium causes osteomalacia and renal damage, the itai-itai pattern, alongside emphysema
• Arsenic causes skin, lung and bladder cancer as well as neuropathy and characteristic palmar hyperkeratosis