NEBOSH Chemical and Biological Hazards 2 — Questions and Answers
Question 1: What is the difference between a WEL 8-hour TWA and a WEL short-term exposure limit (STEL)?
- There is no difference, they are the same measurement
- The 8-hour TWA is the average concentration over a full shift, while the STEL is the maximum concentration over any 15-minute period (Correct answer)
- The TWA applies to dust and the STEL applies to gases only
- The TWA is for outdoor work and the STEL is for indoor work
Correct answer: The 8-hour TWA is the average concentration over a full shift, while the STEL is the maximum concentration over any 15-minute period
The 8-hour TWA (Time-Weighted Average) is the average concentration over a standard 8-hour working day. The STEL (Short-Term Exposure Limit) is the maximum concentration over any 15-minute reference period during the working day. STELs prevent excessive short-term peaks even when the 8-hour TWA is met.
Question 2: Under COSHH 2002, what is the hierarchy of control measures for hazardous substances?
- PPE first, then ventilation, then substitution
- Elimination, substitution, engineering controls (enclosure/LEV), administrative controls (safe systems of work), and PPE as a last resort (Correct answer)
- Training first, then monitoring, then PPE
- Risk assessment only, with no mandatory controls
Correct answer: Elimination, substitution, engineering controls (enclosure/LEV), administrative controls (safe systems of work), and PPE as a last resort
COSHH follows the hierarchy: (1) eliminate the substance or process, (2) substitute with a less hazardous alternative, (3) engineering controls such as total enclosure, partial enclosure with LEV, or general ventilation, (4) administrative controls including safe systems of work, reduced exposure time, and hygiene measures, (5) PPE as a last resort when other measures are insufficient.
Question 3: What is Legionella and where is it commonly found in the workplace?
- A chemical found in cleaning products
- A bacterium found in water systems that can cause Legionnaires' disease, commonly found in cooling towers, hot and cold water systems, spa pools, and humidifiers (Correct answer)
- A virus transmitted through food contamination
- A fungus growing on damp walls
Correct answer: A bacterium found in water systems that can cause Legionnaires' disease, commonly found in cooling towers, hot and cold water systems, spa pools, and humidifiers
Legionella pneumophila is a bacterium that thrives in water temperatures between 20-45°C. It is commonly found in cooling towers, hot and cold water systems (especially where water stagnates), spa pools, humidifiers, and decorative fountains. Inhalation of contaminated water droplets (aerosols) can cause Legionnaires' disease, a severe form of pneumonia.
Question 4: Which GHS signal word indicates the more severe level of hazard?
- Caution
- Warning
- Danger (Correct answer)
- Alert
Correct answer: Danger
GHS uses two signal words: 'Danger' for the more severe hazard categories and 'Warning' for less severe categories. Only one signal word appears on a label. If a product has multiple hazards, the most severe signal word takes precedence. 'Caution' and 'Alert' are not GHS signal words.
Question 5: What is health surveillance and when is it required under COSHH 2002?
- Annual health checks for all employees regardless of exposure
- Monitoring the health of employees who are exposed to substances linked to identifiable diseases or adverse health effects, where there is a reasonable likelihood of the condition occurring and valid techniques exist to detect it (Correct answer)
- Blood tests for new employees only
- Surveillance cameras monitoring employee behaviour around chemicals
Correct answer: Monitoring the health of employees who are exposed to substances linked to identifiable diseases or adverse health effects, where there is a reasonable likelihood of the condition occurring and valid techniques exist to detect it
Health surveillance under COSHH Regulation 11 involves systematic health monitoring of employees exposed to hazardous substances. It is required when: there is an identifiable disease or adverse effect linked to the exposure, there is a reasonable likelihood it may occur under the conditions of work, and valid detection techniques exist (e.g., lung function tests for respiratory sensitisers, skin checks for dermatitis-causing agents).
Question 6: What are blood-borne viruses (BBVs) and which occupational groups are most at risk?
- Viruses that affect blood pressure, mainly affecting office workers
- Viruses transmitted through contact with infected blood or body fluids, including hepatitis B, hepatitis C, and HIV, with healthcare workers, emergency services, and laboratory staff at highest risk (Correct answer)
- Viruses spread through airborne transmission only, affecting outdoor workers
- Bacterial infections of the bloodstream affecting food handlers
Correct answer: Viruses transmitted through contact with infected blood or body fluids, including hepatitis B, hepatitis C, and HIV, with healthcare workers, emergency services, and laboratory staff at highest risk
Blood-borne viruses (BBVs) including hepatitis B (HBV), hepatitis C (HCV), and HIV are transmitted through contact with infected blood or body fluids via needlestick injuries, sharps, splashes to mucous membranes, or broken skin. Healthcare workers, emergency responders, laboratory staff, waste handlers, and those working with used needles face the highest occupational risk.
NEBOSH Chemical and Biological Hazards 2
What is the difference between a WEL 8-hour TWA and a WEL short-term exposure limit (STEL)?