Indoor Heat Illness - Cal/OSHA

A building under construction is an outdoor jobsite on the day the foundation goes in and an indoor workplace months later, and California's heat rules follow that change. Title 8, Section 3396, the indoor heat illness standard, took effect July 23, 2024. It applies to indoor work areas at 82°F or more, and requires measured temperatures, engineering controls, and more once the temperature or heat index reaches 87°F. This Cal/OSHA Indoor Heat Illness Toolbox Talk covers when a construction job moves from the outdoor rule to the indoor one, and what the indoor rule requires.

Where the boundary of this talk sits#

This talk covers Section 3396 and how it applies on construction projects. The outdoor rule, Section 3395, belongs to the Cal/OSHA heat illness prevention talk; heat illness first aid and hydration belong to their own talks.

The anchor#

Here is the distinction that carries this whole talk: on a construction job, the heat rule is decided by the building, not the calendar — Section 3396 defines "indoor" as a space under a ceiling or overhead covering that restricts airflow and enclosed along its entire perimeter by walls, doors, windows, or other barriers that restrict airflow, whether open or closed, and says every work area that is not indoor is outdoor and covered by Section 3395 — so the day the roof deck and the last exterior wall close in a floor, that floor's crew changes rulebooks, and a closed-in building with no air movement can be hotter than the street outside.

Indoor or outdoor?#

The definition in Section 3396(b) has two parts, and both must be true. The space must be under a ceiling or overhead covering that restricts airflow. And it must be enclosed along its entire perimeter by walls, doors, windows, dividers, or other physical barriers that restrict airflow — whether those openings are open or closed.

On a building under construction, that means:

• A structural frame with no roof, or a floor with the roof on but open sides, is outdoor — Section 3395 applies.
• A floor with a roof or deck above and walls, windows, or barriers all the way around is indoor — Section 3396 applies, even if the windows or doors are open.

Section 3396(b) is plain about the rest: all work areas that are not indoor are considered outdoor and covered by Section 3395. The supervisor's job is to know, floor by floor, which one applies this week.

When the indoor rule applies#

Section 3396(a)(1) applies to all indoor work areas where the temperature equals or exceeds 82°F when employees are present.

Section 3396(a)(2) turns on the full rule, including the assessment and control measures in subsection (e), when any of these is true:

• the temperature equals or exceeds 87°F when employees are present;
• the heat index equals or exceeds 87°F when employees are present;
• employees wear clothing that restricts heat removal and the temperature equals or exceeds 82°F; or
• employees work in a high radiant heat area and the temperature equals or exceeds 82°F.

The rule defines clothing that restricts heat removal as full-body clothing covering the arms, legs, and torso that is waterproof, designed to protect against chemical, biological, physical, radiological, or fire hazards, or designed to protect the wearer or work process from contamination. A crew in full-body protective suits for abatement, or working near a heat source such as a torch or a curing process, reaches the full rule at 82°F, not 87°F.

There are exceptions, including teleworking, emergency operations, and brief exposures of less than 15 minutes in any 60-minute period between 82°F and 95°F — but the brief-exposure exception does not cover vehicles without working air conditioning or shipping containers during loading and unloading.

Water and cool-down areas#

Under Section 3396(c), potable drinking water must be provided free of charge, fresh, suitably cool, as close as practicable to where people work and in indoor cool-down areas, in enough quantity for one quart per employee per hour for the entire shift.

Under Section 3396(d), cool-down areas must be kept below 82°F unless the employer shows that is infeasible. A worker who takes a preventative cool-down rest must be monitored and asked about symptoms, encouraged to stay in the cool-down area, and not ordered back to work until any symptoms have gone away — and in no event less than five minutes. On a closed-in floor with no power for cooling yet, finding a place below 82°F takes planning.

Measure, record, and control#

Section 3396(e)(1) requires the employer to measure both the temperature and the heat index and record whichever is greater. Measurements are taken first when it is reasonable to suspect the full rule applies, and again when conditions are reasonably expected to be 10 degrees or more above the previous measurement. The records are kept for 12 months or until the next measurements are taken, whichever is later, and made available to employees, their designated representatives, and Cal/OSHA.

Section 3396(e)(2) then sets an order of controls:

• Engineering controls — to reduce the temperature and heat index below 87°F when employees are present, or the temperature below 82°F where employees wear clothing that restricts heat removal or work in high radiant heat areas. On a construction site that can mean fans, temporary air conditioning, ventilation, or isolating heat sources.
• Administrative controls — where engineering controls are not enough. The rule lists acclimatizing employees, rotating employees, scheduling work earlier or later in the day, using work/rest schedules, reducing work intensity or speed, reducing work hours, changing required work clothing, and using relief workers.
• Personal heat-protective equipment — where both are not enough, such as water-cooled or air-cooled garments, cooling vests, wetted over-garments, heat-reflective clothing, or supplied-air personal cooling systems.

New workers, heat waves, and emergencies#

Section 3396(g) requires close observation by a supervisor or designee of any employee newly assigned to a work area at 87°F or more (or 82°F or more with restrictive clothing or in a high radiant heat area) for the first 14 days of employment, and — where no effective engineering controls are in use to control the effect of outdoor heat on indoor temperature — of all employees during a heat wave. Section 3396(f) requires written emergency response procedures, including communication, contacting emergency medical services, and monitoring employees who show signs of heat illness. Section 3396(h) requires training for employees and supervisors, and Section 3396(i) requires a written Heat Illness Prevention Plan, in English and the language understood by the majority of employees, available at the worksite. The plan can be part of the employer's Injury and Illness Prevention Program.

Where the duty sits#

8 CCR 3396 carries the indoor duty: (a) scope at 82°F and the full rule at 87°F or 82°F with restrictive clothing or radiant heat; (b) the definition of indoor; (c) water; (d) cool-down areas below 82°F; (e) measuring, recording, and controls; (f) emergency response; (g) acclimatization; (h) training; (i) the written plan. 8 CCR 3395 covers every work area that is not indoor.

What can go wrong?#

• A floor is closed in over the weekend and the crew keeps working under outdoor-rule habits.
• Nobody measures the temperature on the top floor under a new roof deck in August.
• The only "cool-down area" is the same unventilated floor.
• An abatement crew in full-body suits works at 84°F with no controls because "it's under 87."

How do we manage this properly?#

• Decide indoor or outdoor, floor by floor — roof overhead and closed perimeter means Section 3396.
• Measure and record — temperature and heat index, the greater of the two, kept at least 12 months.
• Control in order — ventilation and cooling first, then work schedules and rotation, then cooling PPE.
• Cool-down area below 82°F — with water, close to the work.
• Watch the new and the heat wave — first 14 days, and everyone during a heat wave if no effective engineering controls are in use.
• Written plan — in English and the crew's language, at the worksite.

Before you start#

Ask which floors or areas are now indoor. Check the latest temperature and heat index readings for those areas. Confirm where the cool-down area is and that it is below 82°F.

Talk it over#

• Which areas of this building are indoor now, and which are still outdoor?
• Where is the hottest spot on this job right now?
• What would help most on a hot, closed-in floor — fans, cooling, earlier hours?

The bottom line#

California's heat rule follows the building. Until a work area has a roof or overhead cover and is enclosed all the way around, Section 3395 applies. After that, Section 3396 applies at 82°F, and at 87°F — or 82°F with restrictive clothing or radiant heat — it requires measuring and recording, engineering controls first, a cool-down area below 82°F, and close watching of new workers.

Frequently asked questions about Cal/OSHA indoor heat#

Does the indoor heat rule apply to a building under construction?

Once the work area meets the definition of indoor in Section 3396(b): under a ceiling or overhead covering that restricts airflow, and enclosed along its entire perimeter by walls, doors, windows, or other barriers that restrict airflow, whether open or closed. Until then, the area is outdoor and Section 3395 applies.

Download the Cal/OSHA indoor heat illness toolbox talk PDF#

Download this Cal/OSHA Indoor Heat Illness Toolbox Talk as a printable PDF in English and Spanish, and review it the week the building closes in.

Related toolbox talks#

• Heat Stress
• Hydration
• First Aid and AED
• Emergency Response

Sources#

• Cal/OSHA, Title 8 CCR §3396 — Heat Illness Prevention in Indoor Places of Employment ((a)(1) indoor work areas at 82°F or more; (a)(2) full rule at 87°F temperature or heat index, or 82°F with clothing that restricts heat removal or in high radiant heat areas; exceptions including brief exposure under 15 minutes in 60 between 82°F and 95°F; (b) definitions of indoor, heat index, clothing that restricts heat removal, high radiant heat area, heat wave; all non-indoor work areas covered by §3395; (c) one quart per employee per hour; (d) cool-down areas below 82°F, rest of at least five minutes; (e) measure and record the greater of temperature and heat index, records 12 months, engineering, administrative, and personal controls; (f) emergency response; (g) 14-day observation and heat waves; (h) training; (i) written plan; operative 7-23-2024): https://www.dir.ca.gov/title8/3396.html
• Cal/OSHA, Title 8 CCR §3395 — Heat Illness Prevention in Outdoor Places of Employment: https://www.dir.ca.gov/title8/3395.html

Written by FieldSafetyTalk's safety professional — a CSP, ASP, CHST and OSHA Authorized Outreach Trainer with 14+ years of international construction safety experience across federal, heavy civil, and industrial projects.

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