Management of combustible, toxic, and oxygen-displacing gases MCQs With Answer

Management of combustible, toxic, and oxygen-displacing gases MCQs With Answer

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Introduction

Managing combustible, toxic and oxygen-displacing gases is a critical component of hazards and safety management in pharmaceutical operations. This quiz collection focuses on practical principles—gas properties, detection technologies, ventilation and inerting strategies, exposure limits, cylinder handling, emergency response and confined-space precautions. Questions are designed to test both conceptual understanding and applied decision-making relevant to M.Pharm professionals responsible for process safety, laboratory safety and regulatory compliance. Use these MCQs to reinforce protocols for preventing fires, explosions, asphyxiation and poisoning, and to prepare for risk assessments, monitoring program design, and emergency planning in pharmaceutical manufacturing and research settings.

Q1. Which statement correctly defines the Lower Explosive Limit (LEL) of a combustible gas?

  • The maximum concentration of gas above which combustion cannot occur
  • The lowest concentration of gas in air at which a propagating flame can occur
  • The concentration that causes asphyxiation by oxygen displacement
  • The concentration at which gas sensors stop responding

Correct Answer: The lowest concentration of gas in air at which a propagating flame can occur

Q2. What is the primary difference between flash point and autoignition temperature?

  • Flash point is a property of gases; autoignition is only for solids
  • Flash point is the lowest temperature at which vapour forms an ignitable mixture with air when an ignition source is present; autoignition is the temperature at which a substance ignites without an external flame or spark
  • Autoignition is always lower than flash point
  • Flash point measures toxicity, autoignition measures volatility

Correct Answer: Flash point is the lowest temperature at which vapour forms an ignitable mixture with air when an ignition source is present; autoignition is the temperature at which a substance ignites without an external flame or spark

Q3. Which control is most appropriate to prevent oxygen-displacement hazards in confined-space entry when inert gases are used?

  • Rely on brief manual checks of oxygen using a single-entry reading
  • Continuous forced ventilation combined with continuous oxygen monitoring and permit-required confined-space procedures
  • Use only administrative controls and worker training without monitoring
  • Seal the space completely and enter immediately to check conditions

Correct Answer: Continuous forced ventilation combined with continuous oxygen monitoring and permit-required confined-space procedures

Q4. Which exposure limit metric indicates an atmosphere immediately dangerous to life or health (IDLH)?

  • Threshold Limit Value (TLV)
  • Permissible Exposure Limit (PEL)
  • LC50 (lethal concentration 50%)
  • IDLH value defined to represent a concentration that poses an immediate threat to life or health

Correct Answer: IDLH value defined to represent a concentration that poses an immediate threat to life or health

Q5. Which sensor technology is typically used to detect combustible hydrocarbon gases in the 0–100% LEL range?

  • Electrochemical sensor
  • Photoionization detector (PID)
  • Catalytic bead (pellistor) sensor
  • Infrared CO2 sensor

Correct Answer: Catalytic bead (pellistor) sensor

Q6. For emergency entry into an area suspected of containing an unknown toxic gas, which respiratory protection is most appropriate for first responders?

  • Air-purifying respirator with organic cartridges
  • Powered air-purifying respirator (PAPR) without supplied air
  • Self-contained breathing apparatus (SCBA) with full protective ensemble
  • Disposable N95 mask

Correct Answer: Self-contained breathing apparatus (SCBA) with full protective ensemble

Q7. What is the recommended method to prevent flammable atmospheres in process vessels during maintenance?

  • Introduce small amounts of combustible solvent to dilute the mixture
  • Inert the vessel by blanketing with nitrogen or other inert gas until oxygen and flammable concentrations are outside flammable limits
  • Rely solely on visual inspection of the atmosphere
  • Vent the vessel directly into an enclosed building

Correct Answer: Inert the vessel by blanketing with nitrogen or other inert gas until oxygen and flammable concentrations are outside flammable limits

Q8. Which is the correct practice for storing compressed gas cylinders in a pharmaceutical facility?

  • Store flammable and oxidizer cylinders together to save space
  • Store cylinders horizontally and unsecured
  • Store cylinders upright, secured (chained or strapped), with valve caps in place and segregated by gas class
  • Keep regulators connected and cylinders under pressure at all times

Correct Answer: Store cylinders upright, secured (chained or strapped), with valve caps in place and segregated by gas class

Q9. At what atmospheric oxygen concentration is the environment generally considered oxygen-deficient and hazardous for unprotected workers?

  • Less than 21.0% by volume
  • Less than 20.9% by volume
  • Less than 19.5% by volume
  • Less than 17.0% by volume

Correct Answer: Less than 19.5% by volume

Q10. Which gas is odourless, non-toxic in low concentrations, and commonly causes asphyxiation by oxygen displacement in laboratories and storage areas?

  • Carbon monoxide
  • Nitrogen
  • Chlorine
  • Hydrogen sulfide

Correct Answer: Nitrogen

Q11. What is the purpose of a bump test for portable gas detectors?

  • To calibrate the instrument’s sensors to a reference concentration
  • To verify the detector responds to a gas source before use (functional check)
  • To replace the sensor element
  • To measure long-term exposure trends

Correct Answer: To verify the detector responds to a gas source before use (functional check)

Q12. Which leak-detection technique provides the highest sensitivity for detecting very small leaks in pressurized systems?

  • Soap-bubble solution
  • Audible listening for hissing
  • Helium mass spectrometer leak detection
  • Visual inspection only

Correct Answer: Helium mass spectrometer leak detection

Q13. In a manufacturing area where VOC vapours are present, which engineering control best reduces the risk of ignition?

  • Use of non-sparking tools only
  • Maintaining concentration below 10% of the LEL by local exhaust ventilation and dilution
  • Relying on administrative rules that prohibit open flames
  • Providing workers with cotton uniforms

Correct Answer: Maintaining concentration below 10% of the LEL by local exhaust ventilation and dilution

Q14. For accidental release of a dense flammable vapor cloud outdoors, which immediate physical mitigation is commonly recommended to reduce explosion risk?

  • Apply foam blanket to vegetation downwind
  • Ignite the cloud to cause a controlled burn
  • Use high-capacity water spray to disperse the vapor cloud and reduce concentration
  • Seal the area with tarpaulins

Correct Answer: Use high-capacity water spray to disperse the vapor cloud and reduce concentration

Q15. LC50 is best defined as which of the following?

  • The lowest concentration that causes irritation in humans
  • The concentration of a substance expected to be fatal to 50% of a test animal population over a specified exposure period
  • The safe exposure limit for workers during an 8-hour shift
  • The concentration triggering an immediate alarm in detectors

Correct Answer: The concentration of a substance expected to be fatal to 50% of a test animal population over a specified exposure period

Q16. Which sensor type is most commonly used for detecting toxic gases such as carbon monoxide or hydrogen sulfide in personal monitors?

  • Catalytic bead sensor
  • Electrochemical cell sensor
  • Flame ionization detector
  • Ultraviolet photometer

Correct Answer: Electrochemical cell sensor

Q17. What is the approximate Lower Explosive Limit (LEL) of methane in air by volume?

  • 1.2% by volume
  • 5.0% by volume
  • 10.0% by volume
  • 15.0% by volume

Correct Answer: 5.0% by volume

Q18. When purging a pipeline that previously contained a flammable gas, which approach is recommended to avoid creating a flammable mixture?

  • Introduce air first then inert gas to dilute the flammable gas
  • Purge with an inert gas (e.g., nitrogen) to displace flammable gas until measurements confirm concentrations are outside the flammable range
  • Open all valves and allow the gas to vent into adjacent enclosed spaces
  • Rapidly cycle between air and flammable gas to confuse ignition sources

Correct Answer: Purge with an inert gas (e.g., nitrogen) to displace flammable gas until measurements confirm concentrations are outside the flammable range

Q19. Which of the following gases is essentially non-toxic but can be lethal by displacing oxygen in an enclosed space?

  • Carbon monoxide
  • Hydrogen sulfide
  • Argon
  • Chlorine

Correct Answer: Argon

Q20. In the event of a large chlorine gas release in a pharmaceutical plant, what is the first priority for site management and emergency responders?

  • Attempt to neutralize the gas with household bleach
  • Ignore evacuation and focus on production continuity
  • Evacuate and isolate the area, move upwind/uphill, and deploy trained HAZMAT teams in appropriate PPE (SCBA and chemical suits)
  • Direct untrained staff to use oxygen cylinders for rescue without protective gear

Correct Answer: Evacuate and isolate the area, move upwind/uphill, and deploy trained HAZMAT teams in appropriate PPE (SCBA and chemical suits)

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