Most masks offer no protection from pollution or tear gas
In the early stages of the Occupy Central movement, many demonstrators were dressed in protective gear, including medical surgical masks or respirators such as the N95. These masks were tested when security forces fired tear gas into the crowd.
In Beijing, face masks are a ubiquitous accessory for residents as the capital is frequently blanketed by thick pollution.
Last month, several participants of the Beijing International Marathon wore full-face Darth Vader-like respirators as pollution reached 344 on the PM2.5 scale. That's almost 11 times the recommended limit set by the World Health Organisation.
Does protective gear provide a sufficient barrier against potentially harmful particles in these situations? Alarmingly, safety experts say the equipment has mostly been misused.
Masks are designed to be used in different conditions. The Self-Contained Breathing Apparatus, also called the "oxygen tank", safeguards the wearer from elements in the air thanks to an exclusive supply of oxygen. Firefighters use this.
With a Supplied Air Respirator, oxygen generated from a remote system of compressed air is supplied through a hose to the wearer. This is used in a hospital setting.
Respirators with filters that block the inhalation of specific components in the air are another category. For example, the N95 is designed to filter out airborne particles, and the X301 is made to filter out dust.
Then there is the disposable surgical mask - which is actually not considered a respirator.
For protection against tear gas, Professor Ignatius Yu, editor for the Hong Kong Academy of Medicine, recommends wearing a tight-fitting respirator with an appropriate filter, such as a full-face mask with activated charcoal filters that absorb organic matter in tear gas.
"Tear gas comes in particles as well as gaseous forms, so you need protection from both. The usual type of particle filter [mask] will not be able to protect you," he says.
If the user is subjected to the tear gas for extended periods, he recommends the Supplied Air Respirator or Self-Contained Breathing Apparatus, although they limit mobility. Yu says a tight fit ensures the effectiveness of the respirators, so it's important to pick the right type and brand, and get a size that suits the user's facial features.
Lam Shi-kai, director of university safety at Chinese University, concurs and recommends a mask that has been certified.
The N95 Respirator, for example, has been approved by the US National Institute for Occupational Safety and Health for protection from exposure to airborne particles. In a healthcare setting, the mask protects from exposure to biological aerosols including viruses and bacteria.
The X301, on the other hand, is only the national standard in China, Lam says. He suggests another mask, N100, which has a nearly 100 per cent efficiency in filtering airborne particles, and an ability to block smaller particles than the N95.
Surgical masks offer no protection from tear gas. Yu says that surgical masks were designed for medical personnel to wear while performing operations, to prevent bacteria from their oral or respiratory cavity entering the wounds of the patients, or vice versa.
Lam cuts open a surgical mask to reveal its interior of non-woven fibres: a white centre layer sandwiched between two thin layers. "The material in the middle is the same material used to make diapers for babies. If diapers can prevent leakage of urine, it means the masks have some water resistance property that can be used to protect against droplets."
But diapers aren't meant to safeguard against vapours or other elements in tear gas, so neither will a surgical mask.
The N95 or X301 do not protect the wearer from pollution.
Yu says the respirators block containments in particle form only, not gases like ozone and nitrogen dioxide.
"If oxygen can go through it, then other gases like sulphur dioxide can, too," he says.
Heavy smog is a toxic stew of ozone, nitrogen oxide, carbon monoxide from vehicle fumes plus particulate matter suspended in the air. In the mainland, particularly in Beijing, air pollution also consists of sulphur dioxide from power plants that burn fossil fuels.
"When Hong Kong has a high level of air pollutants, the Environmental Protection Department advises people, particular the young or very old or people with respiratory disease, to stay home rather than go out," says Lam.
"That message says one thing: no single type of mask can provide protection against pollution," he says.
Lam says only Supplied Air Respirators would deliver proper protection. But this device is impracticable to use in day-to-day life.
Both experts say there's little that can be done to evade air pollution, apart from trying to avoid the polluted area.