Can the presence of hazardous materials can always be detected by the sense of smell?

No, in most cases, the sense of smell is not a reliable means of identifying the presence of a hazardous materials.

Many hazardous materials have no odor, and others are hazardous at concentrations that are too low to be smelled by most people.

In addition there are many materials that have obnoxious odors but are not otherwise hazardous.