Influencing Factors of Fogging of Medical Goggles

A new type of virus is gradually spreading around the world. The World Health Organization officially named it coronavirus (COVID-19). It is classified as a Class B infectious disease by the Law of the People's Republic of China on the Prevention and Control of Infectious Diseases. It is treated by the Class A infectious disease. Both symptomatic and asymptomatic patients infected with COVID-19 become the source of infection, and droplet and contact transmission are the main transmission routes, while the possibility of aerosol and excrement and urine transmission cannot be ruled out. Medical staff must strictly implement three-level protection in their work to ensure their safety due to strong infectivity, atypical symptoms and the longest incubation period of 24 days. However, the problem of fogging goggles is often encountered in clinical operation, which affects clarity and work efficiency. The influencing factors of fogging of goggles are explained in this article, aiming to provide a reference for the anti-epidemic personnel.
 
1. Influencing factors

1.1 Protective masks

During the fight against the coronavirus epidemic, the State Council issued the Technical Guidelines for the Selection and Use of Masks for the Prevention of Coronavirus Infection for Different Groups to prevent the spread of the epidemic on February 4, 2020, pointing out that medical protective masks are recommended for high-risk exposed personnel such as dedicated wards for patients suffered from COVID-19, all staff in ICU and observation rooms, and medical staff in fever clinics of designated medical institutions. At present, medical protective masks such as N95 and KN95, domestic medical protective masks conforming to the GB19083-2010 standard, medical N95 masks of the US FDA standard, and medical protective masks of the British DS/EN14683 standard can be used. However, there are differences in suitability due to the size of the user's head and face when they are put into use. Some literature points out that the suitability of cup-shaped masks for people with different faces is quite different, because the shape of cup-shaped masks is fixed. At the same time, there are differences in the relationship between sizes of faces and suitability for different genders. Studies have shown that nose width is an indicator related to the suitability of masks for men, and face width and the length of the submandibular arc between the two tragus points are related to suitability for women. However, there is no relevant data to prove the influence of the using time on the suitability as well as the wearing time of N95 from the WHO. Some studies have shown that the effective filtration efficiency of wearing a protective mask like N95 for 2 days can still be maintained above 95%.
 

1. 2 Environment

When the coronavirus occurred, it was winter in China and the ambient temperature was low. Literature shows that fogging of goggles is a common problem in environments with great temperature differences. As the ambient temperature decreases, the saturated vapor pressure of water is lower than the partial pressure of water vapor in the air, and the water vapor condenses into small water droplets to form mist water. There will be obvious fog and water for goggles from indoors to outdoors especially in winter. The ambient temperature is lower than the human body temperature indoors, especially in protective clothing for the prevention and control of the disease; the human body will sweat a lot to dissipate heat; the water vapor will form fog when it meets the cold lens.
 

1.3 Goggles

At present, polycarbonate is often used for medical goggles. Although it has the characteristics of good transparency, good impact strength and no harm to the human body, it is not wear-resistant. Therefore, repeated concentrated cleaning of the goggles will scratch the lens and provide a channel for the fog to remain. There are various types of medical goggles. There is still no unified production standard for medical protective glasses. The anti-fog effect of the lens with the single-sided anti-fog coating is better. The double-sided coating has the best anti-fog effect, and the lens without anti-fog function is not fog resistant. Some studies have shown that the use of iodophor in nasopharyngoscopy has a better anti-fogging effect, and some literature mention that hand sanitizer coating, 95% ethanol coating and other methods also have an anti-fogging effect. Which effect is the best? There is currently no documentary evidence.