Which of the following is not true of hazardous gas?

The assertion that odorants are often added to hazardous gases is true. Many gases that are inherently odorless, such as natural gas and propane, have odorants added specifically to alert individuals to their presence, since an odor can be a crucial early warning of a gas leak or other dangerous situation. This practice is done to enhance safety and enable quick detection.

In contrast, the statement about low concentrations deadening a person's sense of smell does not hold true. Usually, exposure to low concentrations of a gas may not significantly impact the sense of smell. It's often at higher concentrations that significant physiological effects, including olfactory fatigue, can occur, thus making it possible for a person to fail to detect the gas even if it is present.

Understanding the properties and behaviors of gases is essential for ensuring safety measures and protective actions in environments where hazardous gases may be present. Awareness of both the attributes of these gases and the potential physiological effects on human senses is a key aspect of effective gas detection and handling protocols.