Cal/OSHA Indoor Heat Illness Adherence: What the Rules State and How Multi-Site Businesses Can Stay Compliant in 2025

Teresa

21 August 2025

In July 2024, California enacted one of the most sweeping workplace safety regulations in recent memory: Cal/OSHA’s Indoor Heat Illness Prevention Standard (§3396). With indoor temperature thresholds as low as 82°F, restaurants, retail stores, and warehouses are now required to continuously monitor and manage heat exposure—or risk fines up to $162,851 per site.

Here's what facilities managers of commercial buildings in California need to know to protect on-site staff and stay compliant, and why experts say data-driven compliance enabled by technology is your best defense.

Watch the on-demand webinar where Zachary Green, Mysa Co-Founder and COO is joined by Eric Compere, Co-Lead of OSHA Practice Group, Nixon Peabody LLP break down everything you need to know about Cal/OSHA indoor heat illness prevention regulations.‍

What Is the Cal/OSHA’s Indoor Heat Illness Rule?

“This is a regulation driven by real-time environmental conditions, not just planning documents.”

Indoor heat illness prevention protocols outlined under Section 3396 become mandatory when indoor workplace temperatures hit 82°F—with additional requirements kicking in at 87°F or when the heat index reaches 87°F. That threshold drops back to 82°F for workers in high-radiant heat environments (like commercial kitchens) or wearing heat-trapping clothing (like polyester uniforms or coveralls).

If these indoor heat temperatures are hit, employers must provide:

Access to free drinking water and cool-down areas
Acclimatization protocols for new employees or during heat waves
A written heat illness prevention plan
Continuous monitoring of indoor conditions
Feasible engineering and administrative controls to reduce heat exposure

“The obligations are triggered by data,” explained Eric Compere, OSHA compliance attorney and former Cal/OSHA counsel, in a recent webinar on what California’s indoor heat rules mean for business operators. “This is a regulation driven by real-time environmental conditions, not just planning documents.”

National Weather Service HeatRisk index Source

Who Must Comply with Indoor Heat Regulations in California?

Unlike rules for heat illness prevention in outdoor places of employment, this new indoor rule applies to every indoor business, regardless of square footage or number of locations. Compliance gets even more difficult in multi-zone environments—like kitchens, backrooms, or stock areas—where temperature can vary significantly within the same building.

“It’s not enough to check the thermostat in the manager’s office,” says Zach Green, COO of Mysa HQ. “If the stockroom is 87°F and you have no data to prove otherwise, that’s what the inspector will go by.”

The cost of non-compliance is steep. Just a single employee complaint can trigger an inspection that leads to citations costing $20,000–$50,000+ in fines.

Why Manual Temperature Logs Don’t Meet Cal/OSHA Standards

“If Cal/OSHA is the first one to take a measurement, that’s already a problem.”

According to Compere, complaints related to indoor heat illness have jumped 400% year-over-year since 2022, meaning the chances of a retail store or restaurant being inspected by Cal/OSHA have increased significantly.

Many businesses are attempting to comply with Cal/OSHA indoor heat regulations by getting employees to log temperatures manually throughout their shift, or by installing basic temperature sensors. But these compliance strategies come with serious flaws:

Manual temperature logs are prone to human error and hard to verify months later. Plus, the time it takes for an employee to log the temperature throughout the space–and convert that into a heat index reading–is time they could spend serving customers.
Thermostat-only monitoring misses temperature fluctuations across different work zones. For example, most restaurants have thermostats installed in back offices or store rooms, but not in the kitchen or throughout the dining space. These are monitoring gaps that can lead to dangerous high-temperature zones.
Basic sensors often don’t measure humidity. This is a problem because accurate humidity readings are needed to calculate the heat index, which is how temperature thresholds are triggered.

“A lot of inspections begin with one issue: the employer has no idea how hot it is,” says Compere. “If Cal/OSHA is the first one to take a measurement, that’s already a problem.”

Manual thermostats installed in a retail back office.

Best Way to Automate Indoor Temperature & Humidity Monitoring

“If you don’t have the data, you’re not compliant.”

The most reliable way for multi-site organizations to follow Cal/OSHA indoor heat rules is with continuous, automated indoor temperature monitoring.

Energy Management Systems (EMS) like Mysa HQ are a great way to automatically log indoor temperatures 24/7:

Monitor indoor workplace temperature and humidity across all zones with peel-and-stick wireless sensors.
Get alerts in real-time when the indoor heat index approaches 82°F or 87°F.
Log and store data automatically for 12+ months (a Cal/OSHA requirement).
Control HVAC remotely to adjust thermostats quickly.
Verify cool-down zone temperature with wireless sensors.

If your business operates in more than one jurisdiction, having an automated process with data easily accessible remotely becomes even more critical. Several other states, including Washington and Oregon, have active heat standards, with others like Arizona and Colorado following close behind.

“You're going to need a chart to track requirements–different temperature thresholds, recordkeeping mandates, and timelines,” says Compere. “But what’s consistent across states is this: if you don’t have the data, you’re not compliant.”

How an EMS Like Mysa HQ Helps You Stay Compliant & Save Money

“Most Mysa HQ customers see an ROI in under 6 months.”

California’s indoor heat illness prevention rule isn’t going away—it’s expanding. And with the rise in inspections and recordkeeping requirements, facility managers can’t afford to take a wait-and-see approach.

The good news? Technology now makes compliance both achievable and operationally beneficial. With an Energy Management System like Mysa HQ, you can automate Cal/OSHA compliance while improving customer and employee comfort, reducing HVAC costs (think fewer emergency service calls and no more 24/7 AC blasting), and significantly minimizing risk across every location.

“In a typical California location, HVAC costs can run $15,000 to $20,000 per year,” Green said. “With an EMS, you can cut that by 10–30%. Most Mysa HQ customers see a return on investment in under 6 months.”