In which situation must a respirator always be worn?

Wearing a respirator is essential when mixing or filling highly toxic pesticides due to the significant risk of inhalation exposure to harmful pesticides. These materials may release toxic fumes or dust that can be detrimental to health, and the use of a respirator provides a critical barrier against those contaminants. This protective measure is especially important in scenarios where the concentration of toxic substances can be extremely high, and inhalation is a primary route of exposure.

In other situations, such as hauling pesticides or during application, while safety measures are still necessary, the immediate health risk associated with airborne particles or vapors may not be as pronounced as it is when mixing or filling highly toxic pesticides. During cleaning, similar care should be taken, but typically, the conditions wouldn't require a respirator unless the substances being cleaned pose a specific inhalation risk. Thus, the only situation where a respirator must always be worn is when dealing with highly toxic pesticides during mixing or filling processes.