Industrial Hygiene is quantitative study of environmental hazards of a working environment. This could be things like toxins in the air, high levels of noise, inadequate ventilation, poor lighting, or even high levels of vibration.
OSHA’s general duty clause states that employers must furnish for their employees work and a workplace that are free of recognized hazards. This obligates employers to assess their environments for these physical hazards. If an employer has reason to suspect these hazards, they must test and quantify these hazards. If quantities are found to be in hazardous ranges the employer, obviously, must mitigate the hazards to acceptable levels.
OSHA does not specify how often to test for most environmental hazards. Some airborne toxins have standards requiring their testing and frequency, but this is only for a specific few. Obviously if there is no reason to suspect a chemical, such as having Cadmium in a typical office, it does not need to be tested for.
As far as testing frequency for non-specified hazards, OSHA does not have a requirement, other than that employees cannot be overexposed to the hazards. This leaves it up to the employer to make sure that OSHA could test for the hazards any day of the week and not find unsafe conditions. The industry standard is 2-3 years.
*Unless specific citations are shown, all answers are based on interpretations provided by authorized officials. As such, all information is deemed reliable, but not guaranteed.