The perceived temperature during civil engineering work is about 45 degrees.

It’s hardly “late summer” at all. We’re still in the midst of a scorching summer—the harshest conditions for civil engineering work.

The other day, the temperature reached 36 degrees, and the heat index while working on the asphalt was as high as 45 degrees. At my worksite, too, an elderly worker complained of feeling unwell due to heatstroke, and there were even situations where work had to be halted.

Needless to say, thorough heatstroke prevention measures are essential at civil engineering job sites.

But the reality isn't that simple...

WBGT at Civil Engineering Sites

At civil engineering job sites, it is common to install a device that measures the heat index—the “WBGT value”—in the site office. At my job site, we have a policy of posting the WBGT reading prominently so that we can take action whenever it exceeds a certain threshold.

Unlike air temperature, the WBGT index is a measure of the overall “risk of heatstroke” that takes into account factors such as humidity and the intensity of sunlight. It was proposed in the United States in 1954 for the purpose of preventing heatstroke, and the higher the WBGT value, the more likely it is that a work environment poses a risk of heatstroke.

WBGT reference values are defined in four levels—"low metabolic rate," "moderate metabolic rate," "high metabolic rate," and "extremely high metabolic rate"—based on the intensity of physical work (level of exertion). At civil engineering sites, the top two levels —"high metabolic rate" and "extremely high metabolic rate"—as the basis for implementing heatstroke countermeasures.

For example, tasks such as hauling heavy materials, logging, and laying concrete are considered “high metabolic rate” work sites. Since we civil engineering construction managers and workers are routinely “acclimated to the heat” (having been exposed to heat daily during the week prior to work), we consider a WBGT value of 25–26 to be the standard. This is 26 for work sites with wind and 25 for those without a noticeable breeze.

When the WBGT index reaches 25 or higher, workers should stay hydrated, take extended breaks, and implement measures such as rotating shifts every 15 minutes. Given the physical exertion involved in civil engineering work, if the WBGT index reaches 28–30, the situation becomes extremely dangerous; even workers accustomed to the heat are at very high risk of heatstroke.

Furthermore, if WBGT measurements at a civil engineering site actually exceed the standard threshold, specific measures will be taken to lower that value. We lower the WBGT value by spraying water to cool the site or by installing fans or dry mist systems at the work site. In my experience, dry mist is the most efficient method for lowering the WBGT value, so if site conditions allow for its installation, it is definitely recommended to install a dry mist system.

The Risks of Not Setting Up a Site House

Construction sites where work is proceeding without a site office are particularly dangerous during extreme heat. While many sites choose not to set up a site office due to on-site conditions, sites that do not have one during this time of year are extremely dangerous.

Even when taking a break at an outdoor worksite, the body heat of workers wearing helmets and other protective gear while working outside does not dissipate easily. No matter how much they hydrate, continuing to work while their body heat remains trapped is extremely dangerous, and worksites without a shelter are hazardous.

When the heat index starts to rise, you have to go inside the on-site greenhouse and use the air conditioning to cool down. Work sites where that’s not possible are quite grueling.

Construction Schedule with Staggered Work Hours

Therefore, at job sites without on-site housing, I prepare a document revising the working hours for August and September in the construction plan—taking the workers’ physical well-being into account—and submit it to the local government office.

Temperatures peak between 10:00 a.m. and 3:00 p.m. during this time of year, and the sun is also at its strongest during these hours. Therefore, to reduce the workload, work hours are divided into two shifts—two hours from 8:00 a.m. to 10:00 a.m. and four hours from 3:00 p.m. to 7:00 p.m.—and workers are rotated between them.

As a result of shifting my work hours, my daily work hours have actually become shorter, but when I add up the total time spent working and taking breaks during the hottest part of the day, I’ve found that shifting my schedule leads to much higher work efficiency.

What saps the stamina of construction workers is the heat and, above all, the “sunlight.” Continuous exposure to sunlight increases the risk of heatstroke. If we are to prioritize the safety of workers, wouldn’t it be the right choice to submit a construction plan that adjusts work hours to avoid direct sunlight?