TOYAMA, Japan -- As Japan heads into the peak of its summer heat and humidity, the country's factories are grappling with how to protect their workers from both the coronavirus and rising temperatures at the same time.
One window-and-door-parts factory about 400 km north of Tokyo has been at the forefront of this dilemma. On a cloudy day in July, the inside of YKK AP's Kurobe Ekko plant registered at 25 C and 80% humidity -- enough to make a masked person sweat from just walking across its floor.
While most of the workers were wearing a regular mask, enduring the heat, a handful were instead using a clear, plastic shield covering the lower half of their faces.
Wearing masks for extended periods of time in extreme temperatures or humidity is said to increase the risk of heatstroke. The company spent about a month testing different mask alternatives to ensure its employees could work safely.
"The productivity of our lines also depends on the motivation of our workers," said the company executive in charge of YKK AP's Kurobe Ekko plant.
The choice came down to either a transparent full-face shield or mouth shield, both of which trap less heat than a conventional mask. "They let us see our workers' faces and expressions, so it was easy to tell whether they were feeling well," said the executive.
About 15 lock makers, who work in relatively close quarters, tested the options and found both to be more comfortable than regular masks. But the face shield caused some glare that made it difficult to see the finer components of the locks.
There was concern that the mouth shield alone would not provide enough protection against respiratory droplets. So the company used a special laser contraption normally used to test ventilation systems to track the airflow from a cough -- finding that the mouth shield diverts most of the airflow upwards, away from other people.
"It's not like we analyzed the trajectory of droplets using a supercomputer, so this does not mean that mouth shields are better than masks," one manager stressed. But it showed the shields do provide some protection, especially combined with other precautions against infection. YKK AP plans to gradually increase the number of workers using mouth shields.
According to Japan's labor ministry, 829 people suffered heatstroke at work in 2019. Those in manufacturing accounted for the most cases at 184, overtaking the construction industry.