CMC Cheat Sheet 2026

The 30 highest-yield CMC facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. After gas freeing, a Marine Chemist tests a tank and finds oxygen at 20.9%, LEL at 0%, and no toxic gases detected. The certificate issued should be: → Safe for workers — Hot Work and Cold Work
2. What is the ACGIH TLV-TWA for benzene? → 1 ppm
3. According to NFPA 306, which of the following locations requires a Marine Chemist's certificate before commencing hot work? → On a pipeline connected to a fuel tank that has been emptied and cleaned.
4. What is the minimum oxygen concentration by volume required in a cargo tank atmosphere before personnel may enter for cleaning or inspection? → 19.5% by volume
5. When testing a deep or stratified atmosphere within a permit-required confined space, what is the OSHA-recommended practice for positioning the sampling probe? → Test at approximately 4-foot intervals in the direction of travel and to each side.
6. What role does the SOLAS Convention play in maritime safety? → SOLAS sets regulations for life-saving equipment and safety measures on ships.
7. What is 'clingage' in the context of cargo tank cleaning operations? → Cargo residue that adheres to tank surfaces and cannot be removed by pumping alone
8. What role does personal protective equipment (PPE) play in hazardous materials management? → PPE is essential for protecting workers from hazardous materials exposure.
9. What is containment in hazardous materials management? → Containment involves preventing hazardous materials from escaping into the environment.
10. Why must catalytic bead sensors NOT be used in oxygen-deficient atmospheres? → Combustion on the bead requires sufficient oxygen to function accurately
11. Before conducting gas freeing operations on a tanker, what must be completed to prevent static electricity ignition? → Bond and ground the vessel to the terminal or yard
12. Why is proper chemical sampling technique important? → Proper sampling ensures accurate and reliable results for risk assessment and compliance.
13. What is the IDLH (Immediately Dangerous to Life or Health) concentration for hydrogen sulfide (H2S)? → 100 ppm
14. Why is it important to understand chemical properties during sampling? → Understanding chemical properties ensures safe handling, sampling, and storage.
15. In cargo tank cleaning operations, what does 'tank stripping' refer to? → Pumping out the maximum possible cargo residue before washing begins
16. When calibrating a multi-gas detector for marine use, what gas mixture is typically used for LEL calibration? → 50% LEL methane in air
17. What are chemical safety data sheets (SDS)? → SDS include information on chemical hazards, handling, and emergency measures.
18. To maintain their status, a Certified Marine Chemist must undergo recertification. What is the standard interval for this recertification process? → Every five years.
19. What does 'Retention on Board' (ROB) refer to in the context of cargo tank cleaning and Marine Chemist certification? → Cargo residue remaining in the tank after discharge that must be documented under MARPOL
20. Which gas detector principle is LEAST affected by silicone contamination? → Infrared (IR) sensor
21. Which ventilation method is most effective for gas freeing a deep cargo tank with multiple toxic gas layers? → Forced mechanical ventilation with ducting extended to the tank bottom
22. What is "inerting" a cargo tank, and when is it used in marine operations? → Replacing the tank atmosphere with inert gas (N2 or CO2) to prevent ignition
23. Which agency enforces MARPOL Annex II cargo tank cleaning and discharge requirements for chemical tankers operating in United States waters? → The United States Coast Guard (USCG)
24. According to the scope of NFPA 306, the standard applies to which of the following scenarios? → Land-side storage tanks located within the boundaries of a shipyard.
25. A Marine Chemist documents a "Not Safe" certificate for a vessel tank. Who has authority to override this certificate and allow entry? → No one — entry is prohibited until a Safe certificate is issued
26. How do environmental regulations relate to maritime safety? → Environmental regulations protect marine ecosystems and control ship pollution.
27. What is the primary purpose of gas freeing a marine cargo tank before issuing a Safe for workers certificate? → To remove flammable, toxic, and inert gases to safe levels
28. When issuing a hot work certificate for a tank that previously contained a flammable liquid, what flammability reading must the Marine Chemist confirm? → LEL reading at or near 0% of the lower explosive limit (typically below 1%)
29. Which of the following standards is the primary document a Certified Marine Chemist applies when evaluating gas hazards on vessels? → NFPA 306 - Standard for the Control of Gas Hazards on Vessels
30. What is the purpose of the ISPS Code? → The ISPS Code enhances the security of ships and port facilities.