California Indoor Heat Illness Prevention Standard: 82°F and 87°F Tiers

California’s indoor heat illness prevention standard, codified at Title 8, Section 3396 of the California Code of Regulations, requires employers to protect indoor workers whenever workplace temperatures reach 82°F. The rule, finalized by Cal/OSHA on July 23, 2024, works in two tiers: a baseline set of protections at 82°F and a fuller set at 87°F that adds engineering controls, measurement, recordkeeping, and close observation of new workers.¹

Who the Standard Covers

Section 3396 applies to every indoor work area in California where the temperature reaches 82°F while employees are present. The rule is not industry-specific. Warehouses, commercial kitchens, manufacturing floors, laundries, and distribution centers are the obvious candidates, but any enclosed space that gets hot enough triggers coverage.¹

A few workplaces are excluded:

Telework locations the employee chooses and the employer does not control.
State prisons operated by the California Department of Corrections and Rehabilitation.
Local jails and juvenile facilities operated by local governments.
Vehicles with effective and functioning air conditioning (excluded only from the 87°F assessment and control measure requirements).

The exemptions are narrow. If employees also move between indoor and outdoor work during a shift, the outdoor heat standard at Section 3395 can apply at the same time as Section 3396; the two are not alternatives.¹

What the 82°F Tier Requires

Once an indoor workspace reaches 82°F with employees present, five things have to be in place: drinking water, access to a cool-down area, an emergency response plan, training, and a written heat illness prevention plan on file.¹

Drinking Water

Water must be fresh, pure, suitably cool, provided at no cost, and located as close as practical to where employees are working. When water is not plumbed or continuously supplied, the employer must have enough on hand at the start of the shift to provide one quart per employee per hour for the entire shift. Starting with less is allowed only if the employer has reliable replenishment procedures so workers can still drink at least a quart per hour.²

Cool-Down Areas and Preventive Rest

Whenever temperatures trigger the standard, employers must maintain a cool-down area kept below 82°F. It has to be shielded from direct sunlight and high radiant heat sources, open to the air or provided with ventilation or cooling, and large enough for workers to sit comfortably without touching each other.¹

Access is not limited to scheduled breaks. Employers must allow and encourage any worker to take a preventive cool-down rest whenever they feel the need. During that rest, the employer must monitor the worker, ask whether they are experiencing symptoms of heat illness, encourage them to remain in the cool-down area, and not order them back to work until symptoms have cleared. In no event can the rest be cut short of five minutes beyond the time needed to reach the cool-down area. If symptoms appear, emergency response procedures take over.

A preventive cool-down rest counts as a “recovery period” under Labor Code Section 226.7, so penalizing a worker for taking one can trigger wage-and-hour liability on top of any safety citation.¹

What Changes at 87°F

The full set of provisions kicks in whenever any of three conditions is met:¹

The temperature or heat index reaches 87°F while employees are present.
The temperature reaches 82°F and employees wear clothing that restricts heat removal, such as chemical-resistant suits or full-body coveralls.
The temperature reaches 82°F and employees work in a high radiant heat area, such as near furnaces, ovens, or heat-radiating industrial equipment.

Humidity matters here. The heat index accounts for how slowly sweat evaporates in humid air, which raises the effective temperature on the body above what a thermometer reads. Employers must track both the raw temperature and the heat index and use whichever is greater.

The Hierarchy of Controls

Section 3396 does not let employers substitute water and rest for actually bringing the temperature down. The regulation requires a hierarchy of controls, worked through in order:¹

Engineering controls first: ventilation, air conditioning, reflective barriers, industrial fans, or insulation to bring the temperature and heat index below 87°F (or below 82°F for workers in restrictive clothing or high radiant heat).
Administrative controls second: when engineering alone cannot bring conditions below the threshold, add measures like adjusted schedules, worker rotation, or shorter shifts during peak heat.
Personal heat-protective equipment third: cooling vests, wetted garments, or other wearable cooling, used when the first two together still fall short.

An employer can skip to the next tier only by demonstrating that the prior control is infeasible. Cost preference is not a feasibility argument.

Measuring and Recording Temperature

At the 87°F tier, employers must measure both temperature and heat index, record whichever is greater, and identify other environmental risk factors in the work area. Each record must include the date, time, and specific location of the measurement and be kept for at least 12 months or until the next set of measurements is taken, whichever is later.¹

Measurements are taken when it is reasonable to suspect the 87°F threshold applies, and again whenever conditions are expected to climb 10 degrees or more above the previous reading. Both should reflect the times during the shift when employee exposure is expected to be highest. Instruments measuring the heat index must produce results consistent with the National Weather Service heat index chart included in the regulation’s appendix. Employees and their union representatives must be involved in planning, conducting, and recording measurements and in identifying environmental risk factors; worker participation is a procedural requirement under the rule.

Acclimatization for New Workers

Any employee newly assigned to a work area where the temperature or heat index reaches 87°F must be closely observed by a supervisor or designee for the first 14 days.¹ Close observation means watching for lightheadedness, dizziness, confusion, and other early signs during the days when the body has not yet adapted.

OSHA and NIOSH recommend the “Rule of 20 percent” for building heat tolerance: a new worker spends only 20 percent of a normal shift in the heat on day one and adds 20 percent each day. On an eight-hour schedule, that is roughly an hour and 40 minutes of heat exposure the first day. Workers returning after a week or more away may also need two to three days to re-acclimatize.³

Emergency Response

Every covered employer must have effective emergency response procedures. The rule requires:¹

Reliable communication, so employees can reach a supervisor or call emergency medical services by voice, observation, or electronic means. Cell phones count only if reception is reliable in the work area.
Immediate and proportional response from the supervisor when symptoms are observed or reported.
Full emergency activation, including a 911 call, when a worker shows signs of severe heat illness such as confusion, vomiting, staggering, disorientation, irrational behavior, or convulsions.
No symptomatic worker left alone or sent home without being offered on-site first aid or emergency medical services.
Precise directions to the facility ready to give responders.

While waiting for paramedics in a suspected heatstroke, the priority is aggressive cooling: move the worker to a cooler area, remove outer clothing, and apply cold water or ice to the head, neck, armpits, and groin. If a large container is available, immerse the worker in an ice bath. Keep someone with them; heat illness can deteriorate quickly.⁴

The Written Plan and Training

Every covered employer must establish, implement, and maintain a written Heat Illness Prevention Plan in both English and the language understood by the majority of the workforce, and keep it available at the worksite to employees and Cal/OSHA representatives on request.¹ At a minimum the plan must cover:

Procedures for providing drinking water and access to cool-down areas.
How the employer will allow and manage preventive cool-down rest periods.
Close observation procedures during the 14-day acclimatization period.
How temperature and heat index will be measured, recorded, and evaluated.
The control measures the employer will use at the 87°F tier.
Emergency response procedures, including how to contact medical services and provide directions to the worksite.
How employees and supervisors will be trained.

Cal/OSHA publishes a downloadable model template employers can adapt. The plan needs updating whenever the facility’s layout changes, new heat-generating equipment is added, or work schedules shift.

Training must reach every supervisory and non-supervisory employee before they begin work that could reasonably result in heat illness exposure. It has to cover how to recognize symptoms, how the employer’s cool-down and emergency procedures work, and what control measures are in use. Supervisors receive additional instruction on monitoring workers and running the emergency response. All training must be delivered in a language the employees understand; for multilingual workforces, that often means more than one session or translated materials.¹ Employers already running outdoor heat training under Section 3395 can combine the two into a single session.

Penalties

Cal/OSHA classifies violations by severity. For a serious violation of Section 3396, the base civil penalty starts at $18,000 and can reach $25,000.⁵ Willful or repeat violations carry a maximum penalty of $162,851.⁶

These are per-violation figures. An employer missing a written plan, lacking cool-down areas, and failing to provide water could face separate penalties for each deficiency. Inspectors can arrive unannounced, and employee complaints are a frequent trigger.

1
Department of Industrial Relations. California Code of Regulations, Title 8, Section 3396 – Heat Illness Prevention in Indoor Places of Employment
2
Department of Industrial Relations. Indoor Heat Illness Prevention – Sufficient Amounts of Drinking Water
3
Occupational Safety and Health Administration. Heat – Protecting New Workers
4
Occupational Safety and Health Administration. Heat-Related Illnesses and First Aid
5
Department of Industrial Relations. California Code of Regulations, Title 8, Section 336 – Assessment of Civil Penalties
6
Department of Industrial Relations. Cal/OSHA Increases Civil Penalty Amounts for 2025