设计外科口罩的初衷是防止外科医生产生的飞沫污染病人。 它并不能有效地阻断小于100微米的颗粒。 而COVID-19颗粒的大小是1-4 微米， 所以如果医生戴外科口罩防病毒， 实际上是把他们自己放到了危险的边缘。
Widely Used Surgical Masks Are Putting Health Care Workers At Serious Risk
scholars, nonprofit leaders and former regulators in the specialized field of occupational safety say relying on surgical masks — which are considerably less protective than N95 respirators — is almost certainly fueling illness among front-line health workers, who likely make up about 11% of all known COVID-19 cases.
Put simply, in worker safety, “a surgical mask is not PPE,” or personal protective equipment, said Amber Mitchell, president and executive director of the International Safety Center and immediate past chair of the occupational health and safety section of the American Public Health Association.
The allowance for surgical masks made more sense when scientists initially thought the virus was spread by large droplets. But a growing body of research shows it’s spread by minuscule viral particles that can linger in the air as long as 16 hours.
A properly fitted N95 will block 95% of tiny air particles — down to three-tenths of a micron in diameter, which is the hardest to catch — from reaching the wearer’s face. But surgical masks, designed to protect patients from a surgeon’s respiratory droplets, aren’t effective at blocking particles smaller than 100 microns, according to mask maker 3M Corp.
A COVID-19 particle is about 1 to 4 microns, according to recent research.
Research from early April, examining two hospitals in South Korea, found surgical masks “seem to be ineffective in preventing the dissemination” of coronavirus particles. A 2013 Chinese study found that twice as many health workers, 17%, got a respiratory illness if they wore a surgical mask treating sick patients, compared with 7% of those who continuously used an N95, per the American Journal of Respiratory and Critical Care Medicine.