Safety, Health, and Environment practice questions

Answer: A) A is more acutely toxic than B

• ACorrect. A lower LD50 means less is needed to be lethal.
• BIncorrect. Lower LD50 means more toxic.
• CIncorrect. Their LD50s differ 100-fold.
• DIncorrect. It's a standard acute toxicity measure.

Answer: A) Removing any one of the three elements (fuel, oxygen or heat) stops the fire

A fire needs fuel, oxygen and heat at the same time, so removing any one of them puts it out. The fire tetrahedron adds the chain reaction, which dry chemical agents interrupt.

• ACorrect. Fire needs fuel, oxygen and enough heat at the same time. Extinguishers work by cooling the fuel, displacing oxygen or interrupting the chemical reaction (the fourth element of the fire tetrahedron).
• BIncorrect. Removing just one element is enough. A CO2 extinguisher, for example, works only by displacing oxygen.
• CIncorrect. Cooling the fuel below its ignition temperature removes the heat element. This is how water extinguishers work, even though fuel is still present.
• DIncorrect. Displacing or removing oxygen takes away the oxidizer and puts the fire out. This is how CO2 extinguishers work.

Answer: C) Whether the credited independent safeguards cut a scenario's frequency to a tolerable risk

LOPA evaluates how reliable each independent protection layer is and whether the layers together reduce a scenario's risk to a tolerable level. HAZOP, FMEA, and consequence modeling serve different purposes.

• AIncorrect. This describes a HAZOP study, a qualitative method for identifying deviations. LOPA often takes HAZOP scenarios as its input.
• BIncorrect. This describes Failure Mode and Effects Analysis (FMEA).
• CCorrect. LOPA is a semi-quantitative method. It starts with the frequency of an initiating event, credits the probability of failure on demand of each independent safeguard, and checks whether the resulting risk is tolerable or more layers are needed.
• DIncorrect. This is consequence (dispersion) modeling. It estimates how severe a release would be, not how much risk reduction the safeguards provide.

Answer: C) Independent of the basic process control system

• AIncorrect. It must be active.
• BIncorrect. That removes independence.
• CCorrect. A shared failure would defeat both layers.
• DIncorrect. It protects at all times.

Answer: C) Flammable liquid Category 3

Under 29 CFR 1910.106, a flammable liquid is any liquid with a flash point at or below 93 °C (199.4 °F), sorted into Categories 1–4. A flash point between 23 °C and 60 °C puts a liquid in Category 3.

• AIncorrect. Category 1 requires a flash point below 23 °C (73.4 °F) and a boiling point at or below 35 °C (95 °F).
• BIncorrect. Category 2 requires a flash point below 23 °C (73.4 °F) with a boiling point above 35 °C (95 °F).
• CCorrect. Category 3 covers flash points at or above 23 °C (73.4 °F) and at or below 60 °C (140 °F). A 50 °C flash point falls in this range.
• DIncorrect. Category 4 covers flash points above 60 °C (140 °F) and at or below 93 °C (199.4 °F). Under the old 100 °F (37.8 °C) cutoff, this liquid would have been called combustible, but under current OSHA rules it is Category 3.

Answer: A) Open the motor's disconnect switch, apply a personal lock, and verify the motor won't start

Lockout/tagout prevents unexpected energization during servicing by locking energy isolating devices, such as disconnect switches, that physically block energy. Control-circuit devices such as push buttons and selector switches do not count.

• ACorrect. A disconnect switch is an energy isolating device: it physically prevents energy from reaching the motor. Locking it and then verifying isolation protects against unexpected start-up during servicing.
• BIncorrect. OSHA states that push buttons, selector switches and other control circuit type devices are not energy isolating devices, so a tag on a stop button does not isolate the energy.
• CIncorrect. A software or control-circuit command does not physically block energy, so the pump could still be energized unexpectedly.
• DIncorrect. Closing the valves addresses process fluid but leaves the electrical energy uncontrolled. Every hazardous energy source has to be isolated.

Answer: D) ACGIH

• AIncorrect. NCEES develops licensing exams.
• BIncorrect. NFPA publishes fire codes.
• CIncorrect. ASME publishes pressure vessel codes.
• DCorrect. OSHA PELs are the enforceable limits.

Answer: C) A process with a listed highly hazardous chemical at or above its Appendix A threshold

PSM covers processes with Appendix A highly hazardous chemicals at or above threshold quantities, or with 10,000 lb or more of flammable liquids or gases. Retail facilities, oil/gas well drilling and servicing, and normally unoccupied remote facilities are excluded.

• AIncorrect. PSM is not triggered just because a chemical needs an SDS. It applies only to listed highly hazardous chemicals at or above threshold quantities, or to 10,000 lb or more of flammable liquids or gases.
• BIncorrect. Paragraph (a)(2) expressly excludes oil or gas well drilling and servicing operations from the standard.
• CCorrect. Paragraph (a)(1) applies the standard to processes involving a chemical at or above the threshold quantity listed in Appendix A, and to processes with 10,000 lb or more of flammable liquid or gas.
• DIncorrect. Paragraph (a)(2) expressly excludes retail facilities, regardless of the quantity stored.

Answer: C) Collapse when pressure falls below atmospheric

• AIncorrect. It protects against underpressure.
• BIncorrect. That's a pressure relief device.
• CCorrect. For example, when pumping out or when vapor condenses.
• DIncorrect. It protects against underpressure.

Answer: C) The case can withstand an internal gas explosion and stop it from igniting the outside atmosphere

Under 29 CFR 1910.399, explosion-proof apparatus contains an internal explosion of a specified gas or vapor, keeps it from igniting the surrounding atmosphere, and stays below an external temperature that could ignite that atmosphere.

• AIncorrect. This describes intrinsically safe equipment, which prevents ignition by limiting energy. Explosion-proof equipment instead contains any ignition that happens inside it.
• BIncorrect. This describes a purged and pressurized enclosure, which is a separate protection method from explosion-proof construction.
• CCorrect. OSHA defines explosion-proof apparatus as enclosed in a case that can withstand an explosion of a specified gas or vapor inside it, can keep that explosion from igniting the surrounding gas, and runs at an external temperature that will not ignite the atmosphere.
• DIncorrect. Explosion-proof enclosures are not designed to be gastight. The OSHA definition assumes an explosion may happen inside the case, which means vapor can get in.