Environmental Health • Occupational health and safety • Comprehensive student notes
Classification and Control of Occupational Hazards
Occupational hazards are conditions, agents or work processes that can harm a worker, a patient, a visitor, the community or the environment. This resource gives emergency-medicine and public-health students a practical system for recognising hazards, assessing risk, selecting controls and responding safely to exposure. It applies to hospitals, laboratories, farms, construction, transport, offices, schools and informal work.
Safety note: These notes support learning and do not replace a facility risk assessment, an occupational-health clinician, an emergency plan, a product safety-data sheet (SDS), radiation-protection rules or Uganda’s current laws and regulations. For a real exposure, protect yourself first, call the local emergency system and follow the employer’s written protocol.
Learning objectives
- Define hazard, risk, exposure, incident, near miss, occupational injury and occupational disease.
- Classify hazards as safety, physical, chemical, biological, ergonomic, psychosocial and environmental/work-organisation hazards.
- Explain how route, dose, duration, frequency and susceptibility influence harm.
- Conduct a documented risk assessment with workers and supervisors.
- Apply the hierarchy of controls, keeping personal protective equipment (PPE) as the last line of defence.
- Describe controls for healthcare, laboratory, agricultural, construction and office hazards.
- Provide first response, referral, reporting and follow-up after common emergencies.
- Use surveillance, immunisation, training and continuous improvement to prevent recurrence.
1. Core terminology
| Term | Meaning | Practical example |
|---|---|---|
| Hazard | Anything with the potential to cause harm, including an agent, task, condition or behaviour. | An exposed electrical conductor, a hepatitis-B-positive blood sample or a wet floor. |
| Risk | The likelihood that harm will occur and the severity of that harm, considering existing controls. | A frequently used unguarded cutter has higher risk than the same cutter locked away. |
| Exposure | Contact between a person and a hazard through inhalation, ingestion, injection, skin, eye or mucous-membrane contact, radiation or physical force. | A splash to the eye, repeated loud-noise exposure or lifting a patient. |
| Incident | An unplanned event that causes or could cause injury, ill health, damage or interruption. | A chemical spill, collision or needlestick. |
| Near miss | An incident with no injury or damage this time but with potential for harm. | A falling cylinder stopped before it hits someone. |
| Occupational injury | Acute physical or psychological harm arising from work. | A fracture after a fall or acute stress after workplace violence. |
| Occupational disease | Illness caused or materially contributed to by workplace exposures or work organisation. | Noise-induced hearing loss, occupational asthma or a work-related musculoskeletal disorder. |
| Control | A measure that removes a hazard or reduces exposure and risk. | Replacing a solvent, enclosing a machine, changing a roster or supplying fit-tested PPE. |
A hazard is not automatically an injury. Harm depends on the hazard’s properties, amount and route of exposure, duration and frequency, task, environment, control effectiveness and the worker’s susceptibility. Children, pregnant workers, older workers and people with chronic disease or disability may need additional assessment and reasonable adjustments.
2. Classification of occupational hazards
| Class | Typical sources | Possible outcomes | Examples of prevention |
|---|---|---|---|
| Safety/mechanical | Falls from height, slips, trips, machines, vehicles, forklifts, falling objects, sharps, electricity, fire, explosions and confined spaces. | Trauma, fractures, amputation, burns, electrocution, asphyxia or death. | Guarding, isolation/lockout, safe traffic plans, housekeeping, permits, rescue plans and training. |
| Physical | Noise, vibration, heat, cold, humidity, poor lighting, ionising/non-ionising radiation, pressure and extreme weather. | Hearing loss, heat illness, hypothermia, cataract, skin injury, decompression illness, fatigue or cancer risk. | Engineering isolation, shielding, ventilation, time limits, monitoring, hydration, rest and hearing/eye protection. |
| Chemical | Gases, vapours, fumes, dusts, mists, solvents, pesticides, disinfectants, laboratory reagents, heavy metals, cytotoxic medicines and cleaning products. | Poisoning, burns, dermatitis, asthma, organ injury, reproductive harm, sensitisation, cancer or fire/explosion. | Elimination/substitution, closed systems, local exhaust, labelled storage, SDS, spill plans and compatible PPE. |
| Biological | Blood/body fluids, respiratory droplets/aerosols, infectious patients, cultures, animals, vectors, sharps, mould and contaminated water/food. | Hepatitis B/C, HIV, tuberculosis and other infections; allergy; bites or occupational asthma. | Standard precautions, vaccination, hand hygiene, ventilation, safe sharps, isolation, waste control and post-exposure care. |
| Ergonomic | Heavy or unpredictable lifting, awkward posture, repetitive movement, force, prolonged standing/sitting, poor workstation design and hand-arm vibration. | Back injury, sprain, tendon disorder, nerve compression, chronic pain and fatigue. | Mechanical aids, team lifting, adjustable workstations, task rotation, micro-breaks and early reporting. |
| Psychosocial | Excessive workload, low control, understaffing, shift/night work, violence, harassment, bullying, discrimination, moral distress, job insecurity and traumatic events. | Anxiety, depression, burnout, sleep disorder, substance misuse, errors, absenteeism, cardiovascular disease and suicide risk. | Safe staffing, respectful leadership, violence prevention, predictable rosters, confidential support and worker participation. |
| Environmental/work organisation | Unsafe water or sanitation, poor ventilation, crowding, waste, extreme temperature, inadequate supervision, fatigue and poor emergency planning. | Infection, heat stress, falls, reduced concentration and amplification of other hazards. | Facility design, maintenance, clean water, sanitation, supervision, adequate breaks and a functioning safety system. |
3. Hazards by work setting
Healthcare and emergency departments
- Sharps and blood exposure: recapping needles, overfilled sharps bins, rushed procedures and unsafe disposal cause percutaneous exposure. Use safety-engineered devices where available, place a puncture-resistant container at point of use, never recap by two hands and report every exposure.
- Respiratory infection: triage coughing patients early, improve ventilation, use source control and the mask or respirator level specified by infection-prevention policy.
- Musculoskeletal injury: use slide sheets, hoists and adequate staff for transfers; do not improvise by lifting a dependent patient alone.
- Medicines and chemicals: cytotoxic drugs, anaesthetic gases, disinfectants and compressed gases need labelled storage, closed handling, spill procedures and trained staff.
- Violence and fatigue: use security and de-escalation plans, buddy systems, adequate breaks and confidential psychological support.
Agriculture and informal work
- Control pesticides through integrated pest management, substitution, closed mixing, labelled containers and re-entry intervals; never decant into drink bottles.
- Prevent machinery and vehicle injuries with guarding, maintenance, exclusion zones and fatigue control. Provide shade, water, rest and heat-illness education.
- Reduce zoonotic disease through animal vaccination, gloves, wound care, safe slaughter and prompt referral after bites or exposure.
Construction, transport and workshops
- Plan work at height, use inspected platforms and fall-arrest systems, protect edges and never work beneath suspended loads.
- Separate people from vehicles with traffic routes, speed control, reversing alarms and high-visibility clothing.
- Control welding fumes, dust, noise and vibration with wet methods, local extraction, enclosure, maintenance, exposure monitoring and appropriate respirators.
4. How exposure becomes harm
| Exposure determinant | Why it matters | Assessment question |
|---|---|---|
| Route | Inhalation, ingestion, injection, skin, eye/mucosal contact, radiation and force have different effects. | How did the hazard reach the body? |
| Dose/intensity | Higher concentration, force, noise or radiation generally increases potential harm. | How strong was the source and was it measured? |
| Duration/frequency | A brief high-intensity event and repeated low-level exposure can both be harmful. | How long and how often does the task occur? |
| Timing | Night work, heat, fatigue and delayed reporting can worsen risk. | Was the worker rested, acclimatised and supervised? |
| Susceptibility | Pregnancy, age, asthma, skin disease, disability and immunosuppression may change protection needs. | Who needs an individual adjustment or referral? |
5. The risk-assessment process
- Prepare and involve workers. Define the task, location, people affected, normal and unusual conditions, contractors and visitors. Workers know how work is actually done.
- Identify hazards. Walk through the workplace, observe tasks, review injury/illness and near-miss reports, read SDSs and equipment instructions, inspect ventilation and ask staff about pain, stress and unsafe shortcuts.
- Identify who may be harmed and how. Consider workers, cleaners, waste handlers, patients, students, pregnant workers, night staff, contractors and the public. Record route and duration.
- Evaluate risk. Estimate likelihood and severity, including the worst credible outcome, then prioritise high-risk and reportable hazards. A matrix supports discussion but cannot replace professional judgement.
- Select controls. Start at the top of the hierarchy: remove or substitute the hazard before relying on procedures or PPE. Choose controls that are feasible, durable and acceptable to workers.
- Implement and communicate. Assign an owner, resources and deadline. Train workers in the actual task, provide supervision and make controls accessible on every shift.
- Verify and review. Inspect, measure where appropriate, ask workers whether controls work, investigate incidents and revise after new equipment, staffing, chemicals, outbreaks or legal changes.
Document the hazard, exposed people, route, existing controls, risk rating, additional action, responsible person, due date and review date. A signed form without implementation is not risk control.
6. Hierarchy of controls
| Level | What it does | Examples | Strength and limitation |
|---|---|---|---|
| 1. Elimination | Removes the hazard completely. | Stop an avoidable sharps procedure; remove a damaged ladder from service. | Most reliable because no exposure remains; may require redesign. |
| 2. Substitution | Replaces the hazard with a less hazardous alternative. | Use a less toxic disinfectant or a low-noise process. | Check that the substitute does not introduce a new hazard. |
| 3. Engineering | Isolates people from the hazard. | Machine guards, local exhaust, safety-engineered sharps, shielding, interlocks, ventilation and lift aids. | Effective when maintained; failures may be invisible without inspection. |
| 4. Administrative/work practice | Changes how, when or by whom work is performed. | Training, rosters, permits, standard precautions, job rotation, signage, audits and drills. | Depends on consistent human behaviour and supervision. |
| 5. PPE | Creates a barrier between worker and hazard. | Gloves, eye/face protection, gowns, hearing protection, footwear, helmets, respirators and fall-arrest equipment. | Last line of defence; can fail through poor fit, damage, heat, misuse or false reassurance. |
Controls should be combined. For example, a laboratory solvent needs substitution or a closed system, local exhaust, a written procedure, training and compatible gloves/eye protection. PPE alone is not an acceptable substitute for feasible source control.
7. Control measures by hazard class
Safety, machinery, electrical and fire hazards
- Design out access to moving parts; guard, interlock and isolate before maintenance.
- Use lockout/tagout or an equivalent verified energy-isolation procedure; only authorised, trained workers should restore energy.
- Keep floors dry and routes clear; repair defects; provide handrails, lighting and inspected ladders/platforms.
- Separate pedestrians and vehicles, secure loads, use seat belts and prohibit phone use while driving.
- Control ignition sources, store flammables correctly, maintain extinguishers and exits, display evacuation routes and practise drills.
- Never enter a confined space without atmospheric assessment, permit, trained attendants, communication, rescue equipment and a non-entry rescue plan.
- For electricity, de-energise and verify before work; never improvise with wet hands or damaged cables.
Physical hazards
- Noise: reduce at the source, enclose or isolate equipment, maintain machines, separate noisy areas, limit exposure time and use a hearing-conservation programme with baseline and repeat audiometry where indicated.
- Vibration: maintain tools, use low-vibration equipment, limit duration, rotate tasks and monitor numbness or blanching fingers.
- Heat: provide cool drinking water, acclimatisation, shade/ventilation, work-rest cycles and a buddy system. Train workers to recognise cramps, exhaustion and heat stroke.
- Cold: use dry layered clothing, warm breaks, shelter and a buddy system; treat confusion or reduced consciousness as an emergency.
- Radiation: apply justification, optimisation and dose limitation; use time, distance and shielding, controlled areas, personal dosimetry and equipment quality assurance. Only authorised staff should operate sources.
- Lighting, glare and pressure: correct lighting and displays, prevent glare, maintain safe illumination and follow specialist decompression/pressure protocols.
Chemical hazards
- Inventory chemicals and keep current SDSs accessible in a language workers understand. Never mix products unless the manufacturer specifically permits it.
- Label every container, including secondary containers; separate incompatibles; secure gas cylinders upright and use correct regulators.
- Prefer closed transfer, premixed products, automated dosing and local exhaust. General room ventilation alone may not control a concentrated source.
- Use chemical-resistant gloves selected for the substance and contact time, eye/face protection, protective clothing and a respirator only after competent assessment and fit testing.
- Provide eyewash and emergency shower facilities where corrosive exposure is possible. Plan spill isolation, notification, containment and waste disposal before using the product.
- For cytotoxic medicines, use designated preparation areas, biological safety controls, closed systems, spill kits and trained staff; manage contaminated linen and waste according to policy.
Biological hazards
- Apply standard precautions to every patient: hand hygiene, risk-assessed gloves/gown/eye protection, respiratory hygiene, safe injection, sharps safety, environmental cleaning and reprocessing.
- Use contact, droplet or airborne precautions when indicated; optimise ventilation and avoid crowding.
- Offer hepatitis-B vaccination to workers with occupational risk and maintain documented immunisation. Use TB and other infection-surveillance programmes according to national guidance.
- Segregate, contain, label, transport and treat infectious waste safely. Do not hand-sort bags or compress waste by hand.
- After a needlestick or mucous-membrane exposure, stop the task, wash skin with soap and water or flush eyes/mucosa with clean water/saline, do not scrub or use caustic agents, report immediately and obtain urgent confidential assessment for HIV/hepatitis testing and time-sensitive post-exposure prophylaxis according to the current protocol.
Ergonomic hazards
- Assess the load, distance, height, grip, posture and frequency before lifting. Use trolleys, hoists, slide sheets and adjustable beds.
- For patient handling, explain the move, lock equipment, coordinate a team leader and use enough staff. “Back education” alone is not a control if the load or staffing is unsafe.
- Set work surfaces and screens to neutral posture, support feet and alternate tasks. Schedule brief movement breaks before pain develops.
- Report early symptoms; timely assessment and modified duties reduce progression to chronic disability.
Psychosocial hazards
- Measure workload, staffing, hours, control, fairness, violence and support through confidential surveys and team discussion.
- Improve staffing and rostering, protect rest periods, reduce unnecessary bureaucracy, clarify roles and involve workers in change.
- Use zero-tolerance policies for harassment and discrimination, confidential reporting, fair investigation and protection from retaliation.
- Prevent violence with environmental design, triage, alarms, security, de-escalation training and post-incident support. Do not expect a lone worker to manage a predictable high-risk situation without backup.
- Offer confidential psychological first aid and referral. Peer support is helpful but must not replace professional care for severe distress, self-harm risk or trauma.
8. PPE: selection and safe use
- Identify the hazard and required performance; a glove that protects against one chemical may be penetrated by another.
- Choose the right size and compatible items. Eye protection must not leave gaps; respirators require the correct model, seal and fit testing where applicable.
- Train workers in inspection, donning, doffing, limitations, cleaning, storage and disposal. Observe technique rather than relying on a signature.
- Replace damaged, contaminated, wet, expired or poorly fitting PPE. Do not share reusable PPE unless it is cleaned and disinfected according to manufacturer instructions.
- Continue source controls, ventilation and safe procedures. PPE should never be used to justify an unsafe exposure level.
9. Occupational health surveillance and prevention
- Pre-placement and periodic assessment: match fitness and reasonable adjustments to the job; do not use screening to discriminate or exclude workers unnecessarily.
- Exposure monitoring: measure noise, radiation, heat, dust or chemicals when a competent professional determines it is needed; compare with current national or recognised occupational limits rather than invented numbers.
- Health surveillance: use symptom review, audiometry, respiratory assessment, skin checks, biological monitoring or other tests only when valid and confidential. Results should trigger prevention, not blame.
- Immunisation and prevention: provide recommended vaccines, hand hygiene supplies, clean water, sanitation, nutrition, rest and education.
- Return-to-work: use confidential clinical assessment and graded or modified duties after injury, illness, pregnancy-related limitations or psychological trauma.
- Worker participation: establish safety committees, near-miss reporting and a non-retaliation policy. Workers must be able to stop imminent danger and seek help without punishment.
10. Emergency response to occupational exposures
| Event | Immediate priorities | Follow-up |
|---|---|---|
| Needlestick, cut or blood splash | Stop safely; wash skin with soap and water; flush eyes/mucosa; do not squeeze, scrub or use bleach; report urgently. | Confidential risk assessment, source testing where lawful, HIV PEP assessment, hepatitis-B vaccination/immunoglobulin decisions and follow-up testing under current protocol. |
| Chemical splash or inhalation | Remove from source; use emergency shower/eyewash for the time specified by the SDS; remove contaminated clothing; call emergency help for breathing difficulty, collapse or extensive burns. | Bring the SDS/container, obtain urgent clinical review and report the spill. Do not induce vomiting unless poison-control guidance specifically instructs it. |
| Fire, explosion or burn | Raise alarm, evacuate, isolate energy only if trained and safe, use extinguisher only for a small fire with an exit behind you. Cool thermal burns with clean running water; do not apply ice or remove stuck clothing. | Emergency evaluation for inhalation injury, electrical injury, deep/large burns and serious trauma; investigate root causes before restarting work. |
| Electrocution | Do not touch the person until power is isolated. Call emergency help, start basic life support/AED when safe and trained, and treat associated trauma. | Urgent medical assessment even if the worker appears well; secure the scene and report the equipment fault. |
| Fall, crush or major trauma | Make the scene safe, call emergency help, control severe bleeding, protect the spine only when indicated and do not move a trapped person without coordinated rescue. | Document, preserve the scene where required, review permits/guarding and provide rehabilitation. |
| Heat illness | Move to a cool place, remove excess clothing, cool rapidly and call emergency help for confusion, collapse, seizure or very hot skin. Do not give fluids to an unconscious person. | Medical review, hydration/rest plan, acclimatisation and work-rest redesign. |
| Violence or traumatic event | Escape to safety, activate security, assess injuries and immediate psychological danger; do not pursue an armed or violent person. | Confidential medical and psychosocial care, incident reporting, legal support if desired and prevention review. |
| Radiation incident | Stop work, leave/secure the area, prevent spread and notify the radiation-safety officer. Do not improvise decontamination without the facility plan. | Specialist dose assessment, contamination monitoring, medical follow-up and regulatory reporting. |
11. Reporting, investigation and improvement
- Report injuries, occupational illnesses, exposures, property damage and near misses promptly through the facility system. Reporting is for prevention, not punishment.
- Provide immediate care first, then preserve relevant evidence such as equipment, labels, CCTV and training records without compromising privacy or rescue.
- Investigate underlying causes using a timeline or “why” analysis: unsafe design, workload, maintenance, procurement, supervision and organisational decisions often matter more than the last worker’s action.
- Develop corrective actions using the hierarchy of controls, assign owners and due dates, communicate lessons learned and verify effectiveness.
- Track leading indicators (training completion, maintenance, inspection findings, near misses) and lagging indicators (injury, illness, lost time). A low injury count may reflect under-reporting.
12. Uganda and public-health practice
In Uganda, employers and health facilities should work within the Occupational Safety and Health Act, 2006, applicable public-health and infection-prevention guidance, labour requirements, environmental regulations and sector-specific standards. Students should locate the current text and local reporting pathway rather than relying on an old handout. District health teams, occupational-health services, facility safety committees and worker representatives should coordinate prevention, surveillance, notification and education.
For every workplace, ask: Is the hazard eliminated where possible? Are controls maintained on every shift? Can a worker report without retaliation? Is emergency care reachable? Are contractors and informal workers included? Are data used to improve the system?
13. Applied learning cases
Case 1: Needlestick during a night shift
A trainee recaps a used needle, is punctured and is told to “keep quiet.” The correct priorities are to stop, wash the site, report immediately, obtain confidential exposure assessment and arrange time-sensitive PEP decisions. Prevention should address point-of-use sharps containers, a no-recapping policy, staffing, supervision and a non-retaliation culture.
Case 2: Solvent smell in a workshop
Workers develop headache while using a solvent in a closed room. Move people to fresh air and seek urgent assessment for severe symptoms; do not re-enter until the source is controlled. Review substitution, closed transfer, local exhaust, storage, SDS training, fire risk and exposure monitoring. A mask chosen without chemical compatibility or fit assessment is not an adequate plan.
Case 3: Repeated back pain in a ward
Several nurses report pain after transferring dependent patients. The solution is not simply a poster about lifting. Observe the task, assess patient weight and predictability, provide hoists/slide sheets, staff the transfer, train and supervise, redesign bed height and monitor early symptoms and injury trends.
14. Self-test
- What is the difference between a hazard and a risk?
- Arrange these in the hierarchy of controls: PPE, substitution, engineering, elimination, administrative controls.
- Name three routes of occupational exposure and three vulnerable groups.
- Why is PPE described as the last line of defence?
- List the immediate actions after a needlestick.
- Give two engineering and two administrative controls for excessive noise.
- What makes psychosocial hazards occupational-health hazards rather than merely personal problems?
- Why should a near miss be reported?
- What information should a risk-assessment record contain?
- Which emergency requires that power be isolated before touching the victim?
Answers
- A hazard has potential to harm; risk combines likelihood and severity after considering exposure and controls.
- Elimination, substitution, engineering, administrative/work-practice controls, PPE.
- Inhalation, ingestion, injection, skin, eye/mucosal contact, radiation or physical force; vulnerable groups include pregnant workers, young/older workers and people with chronic disease or disability.
- It depends on human compliance and fit, can fail or be damaged, and does not remove the hazard at its source.
- Wash with soap and water, flush mucosa/eyes with clean water or saline, do not scrub or use caustics, report immediately and obtain confidential urgent exposure/PEP assessment.
- Engineering: enclosure, isolation or quieter equipment. Administrative: exposure-time limits, rotation, maintenance, training and hearing-conservation monitoring.
- Work organisation, violence, workload and lack of control can cause predictable health effects and errors; employers can prevent them through design and management.
- It reveals system weaknesses before injury and allows corrective action.
- Hazard, exposed people, route, existing controls, likelihood/severity, additional controls, responsible person, deadline and review date.
- Electrocution; isolate or verify the power is off before contact.
Key takeaways
- Classify hazards broadly; a single task may contain several classes at once.
- Assess real exposure and vulnerable people, not just the hazard label.
- Eliminate or control at the source before relying on procedures or PPE.
- Safe systems require maintenance, supervision, worker participation, surveillance and a non-retaliatory reporting culture.
- After an exposure, protect yourself, provide first aid, report urgently and obtain protocol-based medical follow-up.
