GATE Petroleum Engineering Health Safety and Environment in Petroleum Industry Flashcards

24 sample cards from the Health Safety and Environment in Petroleum Industry deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. Differentiate between a manual shutdown system and an automatic shutdown system.

   A manual shutdown is initiated by an operator pressing an ESD push-button/lever upon detecting an abnormal condition; an automatic shutdown is triggered without human intervention by sensors/logic when process parameters (pressure, level, temperature, flow, gas/fire) exceed safe limits.

2. What is the role of field-mounted ESD push buttons in a plant?

   They allow any operator who observes a dangerous situation to manually and immediately initiate shutdown of a unit or the whole plant, providing a human backup to automatic protection layers.

3. In safety instrumented systems, what does the logic chain 'sensor → logic solver → final element' represent?

   It is the basic architecture of a Safety Instrumented Function (SIF): sensors detect the abnormal condition, the logic solver (e.g., PLC) decides, and final elements (ESD valves, trip relays) act to bring the process to a safe state.

4. What does SIL stand for and why is it important for shutdown systems?

   SIL (Safety Integrity Level, SIL 1–4 per IEC 61508/61511) quantifies the reliability/risk-reduction a safety instrumented function must achieve; higher SIL means lower probability of failure on demand ($\text{PFD}$) and greater required integrity.

5. What is the relationship between Safety Integrity Level and Probability of Failure on Demand?

   Higher SIL corresponds to lower PFD. For example, SIL 1 ranges $10^{-1} \leq \text{PFD} < 10^{-2}$, SIL 2 $10^{-2} \leq \text{PFD} < 10^{-3}$, SIL 3 $10^{-3} \leq \text{PFD} < 10^{-4}$, SIL 4 $10^{-4} \leq \text{PFD} < 10^{-5}$.

6. Why must ESD valves typically be fail-safe (fail-closed or fail-open)?

   So that on loss of power, instrument air, or signal, the valve moves to its predetermined safe position automatically, ensuring protection even when the control system or utilities fail.

7. What is the primary purpose of a blowdown system in a petroleum/process plant?

   A blowdown system safely removes (depressurizes/vents) hydrocarbon inventory from process equipment — by routing it to flare or a safe location — to reduce pressure and inventory during emergencies, shutdowns, or maintenance.

8. Differentiate between a blowdown system and a pressure relief (PSV) system.

   A pressure relief valve automatically opens at a set overpressure to protect a single vessel, whereas a blowdown system is intentionally activated (often with ESD) to depressurize the whole system/section in a controlled manner to a flare, typically driven by emergency or fire scenarios.

9. What is the typical API 521 depressuring guideline for blowdown of equipment exposed to fire?

   API 521 recommends depressuring to about $50\%$ of the design/initial pressure (or to $\approx 6.9\ \text{bar / } 100\ \text{psig}$) within about $15$ minutes for equipment exposed to fire, to limit vessel-wall failure from overheating.

10. What is the function of a restriction orifice in a blowdown line?

    A blowdown restriction orifice limits and controls the depressuring (blowdown) flow rate so that the flare and downstream system are not overloaded while achieving the required depressuring time.

11. What components make up the flare/blowdown disposal route?

    Blowdown valves (BDV), blowdown headers, a knockout drum (to remove liquids), liquid seal drum, flare stack, flare tip, and an ignition/pilot system to safely combust the released gas.

12. What is the purpose of a knockout drum in a blowdown/flare system?

    It separates and collects any entrained liquid from the depressured gas stream so that only vapor reaches the flare tip, preventing burning liquid droplets ('flaming rain') from falling out of the flare.

13. What is the main role of a gas detection system in a petroleum facility?

    To continuously monitor the atmosphere for flammable and/or toxic gases, provide early warning of leaks before concentrations become dangerous, and initiate alarms or executive actions (ESD, blowdown) to prevent fire, explosion, or poisoning.

14. What two main categories of gas does a gas detection system monitor, and with what reference units?

    Flammable gases — measured as $\%$ of the Lower Explosive Limit ($\%\text{LEL}$); and toxic gases (e.g., $\ce{H2S}$, $\ce{CO}$) — measured in parts per million ($\text{ppm}$). Oxygen deficiency ($\%\ \ce{O2}$) is also monitored.

15. Define LEL and UEL for flammable hydrocarbon gases.

    LEL (Lower Explosive Limit) is the minimum gas-in-air concentration that will ignite/burn; UEL (Upper Explosive Limit) is the maximum concentration that will burn. Between LEL and UEL the mixture is flammable; outside this range it is too lean or too rich to ignite.

16. What is the LEL of methane, the principal component of natural gas?

    Methane has an LEL of about $5\%$ by volume in air and a UEL of about $15\%$ by volume.

17. Name three common technologies used in flammable gas detectors.

    Catalytic bead (pellistor) sensors, infrared (IR) point and open-path detectors, and (for toxic gases) electrochemical sensors; semiconductor and ultrasonic leak detectors are also used.

18. How does an infrared point gas detector sense hydrocarbon gas?

    Hydrocarbon molecules absorb infrared radiation at characteristic wavelengths; the detector measures attenuation of IR light across a gas-sampling path and correlates the absorption with gas concentration (Beer–Lambert principle).

19. What are typical two-stage alarm set points for a flammable gas detector?

    A low-level (first-stage) alarm at about $20\%\ \text{LEL}$ to warn operators, and a high-level (second-stage) alarm at about $40\text{–}60\%\ \text{LEL}$ that may initiate executive action such as ESD or blowdown.

20. What three elements form the classic 'fire triangle' that fire detection and suppression systems target?

    Fuel, oxygen (oxidizer), and heat (ignition energy). Removing or isolating any one element extinguishes or prevents the fire; the fire tetrahedron adds the chemical chain reaction as a fourth element.

21. Name the main types of fire detectors used in petroleum facilities.

    Heat detectors (fixed-temperature/rate-of-rise), smoke detectors (ionization/optical), and flame detectors (UV, IR, and combined UV/IR) which sense the radiation emitted by flames.

22. How does a UV/IR flame detector identify a hydrocarbon fire?

    It detects the characteristic ultraviolet and infrared radiation emitted by flames (e.g., the $\ce{CO2}$ emission band around $4.3\ \mu\text{m}$ in IR), discriminating real flames from background radiation to reduce false alarms.

23. What fire suppression classification applies to a flammable-liquid petroleum fire, and which agents are suitable?

    It is a Class B fire (flammable liquids/gases). Suitable agents include foam (AFFF), dry chemical powder, $\ce{CO2}$, and clean agents; water spray is used for cooling. Foam works by forming a vapor-sealing blanket that smothers the fuel surface.

24. What is the function of a deluge / water-spray system and a foam system in fire control?

    A deluge water-spray system delivers a large volume of water through open nozzles to cool equipment and control/extinguish fires and protect adjacent structures from radiant heat; a foam system blankets burning hydrocarbon pools to exclude oxygen and suppress flammable vapors, the primary line of defense for tank and pool fires.

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