Japan is rescheduling its outdoor labor force around the heat, not the clock. As temperatures at or above 40°C grow routine, the country's largest construction companies have begun treating summer afternoons as simply unworkable — and official policy is following.
Japan Gives 40°C Days An Official Name
Japan already had a vocabulary for dangerous heat: above 30°C is a "midsummer day" (真夏日), above 35°C a "severe heat day" (猛暑日). But 35°C no longer captures what Japanese summers have become.
The Japan Meteorological Association coined "extreme heat day" (酷暑日) in 2022 for any day exceeding 40°C. On April 17, Japan's Meteorological Agency formally added the term to its forecast vocabulary — an acknowledgment that such temperatures now occur frequently enough to need a name.
The new word was quickly put to use. On August 3, seven observation points simultaneously recorded 40°C or above. Four prefectures — Fukuoka, Kumamoto, Saga, and Kagawa — hit that threshold for the first time in recorded history. By that one day, Japan's cumulative count of 40°C-plus readings in 2026 reached 34, surpassing 2025's full-year total of 30.
Japan's Fire and Disaster Management Agency recorded 7,611 ambulance transports for heat stroke in the week of August 3–9, following 9,180 the week before.
Obayashi Drops The Assumption That Work Hours Are Fixed
Construction giant Obayashi Corporation arrived at shorter hours only after exhausting the alternatives. Since 2025, the firm had required all workers at its sites to wear fan-equipped uniforms and wearable devices flagging heat stroke risk. Site managers tracked work and rest against WBGT — wet bulb globe temperature — indices, and temporary air conditioning was installed where possible.
At a sluice gate renovation project in Edogawa, Tokyo, the measures went further. Workers plunged their hands into ice water before shifts to pre-cool their blood. A refrigerated truck was converted into a rest shelter. Slushie drinks were distributed to cool workers from the inside.
It still wasn't enough. "Individual physical differences mean no amount of equipment can bring the risk to zero," said Keita Yoneda, head of Obayashi's Edogawa Sluice Gate Work Office, in remarks to broadcaster FNN.
Starting July 13, the site changed its schedule. Workers started at 7:30 a.m. and finished by 1:30 p.m., with 10-minute breaks every 50 minutes replacing a formal lunch hour. Actual working time fell from eight hours to six. Wages stayed the same. Three weeks in, no heat stroke cases had been recorded.
The initiative — dubbed "Summer Time Challenge," run jointly with the Ministry of Land, Infrastructure, Transport and Tourism's regional offices — ran through August 7. On May 21, Obayashi extended the model company-wide: all domestic construction sites would shift to 7 a.m.–1 p.m. during July and August, with any schedule delays made up during cooler months.
New Labor Rules Force Companies To Plan For The Worst
Japan's revised Industrial Safety and Health Regulations, in effect since June 1, 2025, require employers to establish heat stroke reporting and emergency response systems whenever the WBGT index reaches 28 or temperatures hit 31°C — for continuous work sessions over an hour, or more than four hours in a day. The rules carry penalties; this is their second summer.
The numbers show why. Japan's Ministry of Health, Labour and Welfare recorded 1,803 workers killed or sidelined for four or more days by occupational heat stroke in 2025 — up 43% from the year before and the highest since records began in 2005. Deaths fell from 31 to 19, which the ministry linked partly to stronger emergency responses prompted by the new rules. Between 2021 and 2025, construction ranked second only to manufacturing in heat stroke casualties — a figure Obayashi cited when it announced its schedule change.
From Wearable Fans To Walk-In Freezer Booths
When whole buildings can't be cooled, Japan has turned to cooling the worker instead. The 7th Kyushu Extreme Heat Countermeasures Exhibition, held June 24–25 in Fukuoka, drew 64 companies and 103 booths. Products ranged from ice vests and semiconductor-cooled garments to a camera-based system that reads a worker's facial color, expression, and sweat to forecast heat stroke risk over the coming hours, cross-referenced against WBGT data.
The most striking entry came from TRUSCO Nakayama: the "Do-Coeemon BOX," launched in April 2026. It is a walk-in personal cooling booth, blasting air as cold as 5°C and holding roughly 15°C inside when outdoor temperatures hit 35°C. The unit retails for ¥1.5 million; since June, distributor Green Cross has offered rentals at ¥300,000 per month, calling it a jobsite "refuge shelter."
The industry's logic is blunt: if a factory floor can't be cooled, cool a workstation; if the workstation is too big, cool the person.
Rethinking Which Hours Are Safe To Work
Japan's construction industry is now restructuring its calendar around the heat. The Japan Federation of Construction Contractors has designated July through September as a shutdown-promotion period and is asking members to schedule consecutive stoppages in mid-August. The Ministry of Land, Infrastructure, Transport and Tourism plans to trial formal "summer construction holidays" from late July through mid-August starting this year.
The common thread is a shift in what gets adjusted — from equipment to schedules. Cooling vests and chilled rest areas help workers endure the heat. Shorter shifts, early start times, and summer pauses with hours recovered in autumn change when work happens at all.
Japan spent years engineering ways to keep working through its summers. As 40°C days outpace the record books, more companies are conceding that some hours shouldn't be worked at all.
