Which of the following is an example of a non-permitted application of LP gas?

The indoor use of portable LP gas heaters without ventilation represents a non-permitted application of LP gas due to serious safety concerns. LP gas appliances, such as heaters, can produce carbon monoxide, a dangerous substance that poses health risks if used in poorly ventilated spaces. Proper ventilation is necessary to ensure that harmful gases are expelled and that oxygen levels remain safe for occupants. Without adequate ventilation, there is an increased risk of suffocation or carbon monoxide poisoning, making this use of LP gas highly unsafe and against regulatory guidelines designed to protect users.

In contrast, options such as outdoor grilling with propane, using LP gas in industrial settings, and heating water using LP gas are common and permitted applications when done with the appropriate safety measures and compliance with regulations. These practices typically include proper equipment, adherence to safety standards, and, when applicable, correct ventilation methods, ensuring that LP gas is used safely and effectively.