Koken, a major Japanese maker of respirators, gas masks and air purifiers, has provided the masks for free to the Japanese Olympic Committee for possible use in training at the Beijing Games.

"These are not the kind of masks that are sold at drug stores to protect yourself from flu or hay fever," said Kohei Kubo, an official at Koken's life safety division.

"They are used at dusty factories and other industrial sites, as well as hospitals, where they are used to prevent infections," he said.

The masks can cut by more than 95 percent the number of small particles that the athletes would inhale, he said.

They are equipped with superlight filters, each weighing 11 grammes (one third of an ounce), and an exhaust valve.

The company recommended the products to the national Olympic committee last year as international concern grew about Beijing's air pollution, Kubo said.

"We provided the products to the committee in mid-July and they are bringing them as a precaution," he said.

Poor air quality in Beijing has prompted International Olympic Committee president Jacques Rogge to warn it could result in the suspension of some events, particularly endurance races such as the marathon.