In a bid to help the public fighting the virus and alleviating anxiety in searching for surgical masks, a taskforce led by the University of Hong Kong-Shenzhen Hospital (HKUSZH), Consumer Council, Hong Kong Applied Science and Technology Research Institute (ASTRI), Hong Kong Science Park (HKSP), and the Department of Architecture and Civil Engineering in the City University of Hong Kong (CityU) is formed. In the past weeks, lab tests were conducted on the efficacy of surgical mask after washing and sterilizing. Scientific analysis of safety and effectiveness was also conducted on do-it-yourself (DIY) face masks which could provide an alternative for the public to alleviate the acute shortage of face masks.
Taking reference to the three-ply design of surgical face mask (water resistant outer layer, middle layer for filtration, inner layer for moisture absorbent), the Taskforce has assessed different materials in producing DIY face masks. Three tests have been conducted in the laboratories of the CUHK and the HKSP:
The tests conducted by the Taskforce included 2 aspects: re-using surgical masks and testing DIY face masks.
The test on re-using surgical masks included washing and sterilizing the surgical masks (spraying 75% alcohol hand rub on the outer layer and washing surgical mask with 60°C soap water). Examination under an electronic microscope revealed that the outer layer of the surgical mask was damaged, losing its filtration and water-resistant functions. The fiber in the middle layer was also damaged, shrunk and deformed that adversely affected the filtration and lost its protection.
The Taskforce advised the public not to wash or sterilize any part of the surgical masks using water, alcohol, detergents, hand wash, soap or any kind of sterilizations.
Reference has been made on the three-ply design of surgical masks in the production of the DIY face masks (water-resistant outer layer, middle layer for filtration, inner layer for moisture absorbent). Moreover, 5 conditions on material selection should be met, namely safety, easy to buy, easy to find, easy to do and easy to wear, to assure the protective function of the home-made face masks and give a peace of mind for the public to buy readily available household items to make face masks for their own use.
●Safety – in compliance with hygiene standard in food handling
●Easy to buy – low-cost
●Easy to find – common household items
●Easy to do – simple to make
●Easy to wear – air permeable with comfort
The Taskforce recommends the following materials:
1.Water-resistant outer layer
Transparent plastic file folder is an optimum choice for face shield (use sun visor or other transparent plastic element made of safe material). To achieve the water-resistant function as a surgical mask, transparent plastic file folder is recommended by the Taskforce to be used as face shield. In the test simulating cough using fluorescent solution, DIY face mask is able to ward off droplets. The cost of a transparent plastic file folder is around HK$2 and it is washable and re-usable.
2.Middle layer for filtration – Kitchen paper towel
Generally, kitchen paper towels meet the hygiene standard in food handling. HKSP scanned kitchen paper towel under electronic microscope and revealed that the fabric size, gaps and layout of kitchen paper towel are similar to that of the middle layer of surgical mask.
3.Inner layer for moisture absorbent – 3-ply / 4-ply pocket / box tissue
Facial tissue is hygienic and soft with strong water absorption. It is suitable for use as the inner layer of face mask. After facial tissue has been chosen, the Taskforce inspected the filtration of DIY face masks that were made of different facial tissues.It is scientifically proved that DIY face mask with one facial tissue (inner layer on the face) and two kitchen paper towels as the outer layer achieved over 90% function of surgical mask in terms of filtration of 20-200nm aerosol. The Taskforce recommends that the public could consider using the above materials to make face mask in time of shortage of surgical mask. The cost of a plastic folder as face shield is around HK$2 and it is re-usable after sterilization. The cost of one-off DIY face mask is around HK$0.2 to HK$0.3.
•Clean your hands completely with handwash and water or alcohol-based hand rub before making and wearing face mask;
•When going out, put a few face masks in a re-sealable zipper storage bag for replacement;
•When wearing a DIY face mask, the inner layer with facial tissue should cover the nose and mouth with kitchen paper towel facing outward. Replace a new DIY face mask timely, say one hour or two, or whenever the facial tissue is wet;
•Never re-use DIY face mask;
•Clean your hands before taking off protective gear. When taking off protective gear at home, get sanitizer readily available. Remove the transparent plastic file folder first and then clean the hands, followed by taking off the DIY face mask that should be discarded in a lidded rubbish bin. Thereafter, wash hands again immediately.;
•Never re-use the material of DIY face mask for other cleaning purposes such as wiping kitchen or bathroom;
•Used plastic file folder should be sterilized with 1:49 diluted household bleach, alcohol-based sanitizer, handwash or dishwashing solution and rinse with water before re-using it. If the plastic file folder is contaminated or broken, do not re-use it. Discard the contaminated plastic file folder in a lidded rubbish bin and wash hands again immediately;
•If you replace face mask in the street, put the used face mask in a sealed bag and discard it in a rubbish bin or bring it home for disposal. Do not litter;
•Put on a surgical mask if you are visiting a high risk location such as hospital or clinic, or when you have any symptoms of upper respiratory tract infection. Seek medical advice immediately if feeling unwell, showing suspected signs of infection or having any upper respiratory tract infection.
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