• The temperature is at least 87° F;
• The heat index based upon Appendix A of Section 3396 is at least 87° F;
• The temperature is at least 82° F where employees are wearing clothing that restricts heat removal; or
• Employees are working in a high-radiant-heat area and the temperature exceeds 82° F,

Temperature and Heat Index Assessment

When one of the above conditions is met, employers must begin measuring the temperature and heat index and record whichever is greater.2

Employers must take initial measurements whenever it reasonably suspects that one of the four conditions above exists where employees are performing work and at times when the heat exposures are expected to be the greatest.

Employers must take subsequent measurements when they reasonably suspect the temperature or heat index is 10 degrees higher than the initial measurements.

When conducting temperature and heat index assessments, employers must maintain records of the measurements for 12 months or until the next measurements are taken. The records must include the date, time, and specific location of all measurements.

Cal/OSHA guidance states that temperature can be measured with a thermometer that is freely exposed to the air but shielded from radiant heat sources, such as the sun, hot objects, hot surfaces, hot liquids, and fire. This air temperature must be measured in the immediate area where workers are located and recorded in degrees Fahrenheit.

Instruments used to measure the temperature or heat index must be used and maintained according to the manufacturer's recommendations. Instruments used to measure the head index must provide the same results as those in the National Weather Service (NWS) heat index chart.

In addition, employers must have effective procedures to obtain the active involvement of employees and their designated representatives in planning, conducting and recording measurements of temperature or heat index, and in identifying and evaluating any other environmental risk factors for heat illness that may exist in the workplace. Risk factors may include:

• Air temperature;
• Air movement;
• Relative humidity;
• Radiant heat from the sun and other sources, like machinery, stoves, ovens, etc.;
• Conductive heat sources, like the floor;
• Workload severity and duration; and
• Protective clothing and PPE worn by workers.

These assessment procedures do not apply to vehicles with effective and functioning air conditioning.

Control Measures

On top of the temperature and heat index assessment, when one of the conditions listed at the top of this section is met, employers must begin using control measures to minimize the risk of heat illness.3

Employers must institute feasible engineering controls to reduce the temperature or heat index below the relevant threshold. Examples include:

• Measures to isolate employees from heat sources used or generated as part of the work duties;
• Air conditioning;
• Cooling fans;
• Cooling mist fans;
• Evaporative coolers (also known as swamp coolers);
• Ventilations to outside air where the outside temperature is cooler than inside;
• Heat exhaust ventilation over hot processes;
• Shielding to block radiant heat; and
• Any other engineering control you may use to reduce the temperature and heat index.

If feasible engineering controls cannot reduce the temperature or heat index below the relevant threshold in a work area, employers must also institute administrative controls to minimize the risk of heat illness in those work areas. Examples include:

• Acclimatization measures;
• Rotating employees from hot areas or using relief workers;
• Scheduling work earlier or later in the day when indoor temperatures may be cooler;
• Reducing work hours or increasing the duration or frequency of rest breaks; or
• Utilizing work clothing that more effectively releases heat.

Where feasible engineering controls can't reduce the temperature or heat index as required and feasible administrative controls aren't effective in minimizing the risk of heat illness, employers must provide personal heat-protective equipment to minimize the risk of heat illness, if feasible. Examples include:

• Water-cooled garments;
• Air-cooled garments;
• Cooling vests;
• Wetted over-garments;
• Heat-reflective clothing; and
• Supplied-air personal cooling systems.

These assessment and control measures apply only under the indoor heat illness prevention standard - not the outdoor heat standard.

According to Cal/OSHA guidance, whether engineering controls are feasible to implement is a fact-sensitive question that includes an evaluation of the size, configuration and location of the indoor workspace; the sources of radiant heat; and the nature of the work being done by workers, among other things. Engineering controls may be infeasible because of technical reasons or due to excessively high cost of implementation. If an employer determines that implementation of engineering controls is infeasible, that would be evaluated on a case-by-case basis in the event of a compliance inspection.

• Employers should consult legal counsel with questions about whether control measures are infeasible based on their specific business operations and circumstances.

1. 8 CCR sec. 3396(a)(2)