Final answer:
The use of a portable heater is typically prohibited in a vehicle cab due to fire hazards and the risk of carbon monoxide poisoning, aligning with safety regulations.
Step-by-step explanation:
Based on safety regulations and common sense, the statement that a portable heater may not be used in any vehicle cab is generally considered to be true. This is because using a portable heater inside the closed space of a vehicle cab poses serious risks, including the potential for fire hazards and carbon monoxide poisoning.
Just as the law of thermodynamics states that a cold object in contact with a hot one never spontaneously transfers energy by heat to the hot object, becoming colder while the hot object gets hotter, in practical scenarios such as with vehicle cabs, the introduction of an external heat source can be dangerous and is typically prohibited for safety reasons.