Price examples:
Numatic Henry Cleaner Bags - 1 Box (Pack of 10)
£7.49
Duck Tape 232318 All Purpose Masking Tape, 50 mm x 50 m.
£4.32
Prices from Amazon. Makes about 30 masks.
A HOME MADE STERILISABLE MASK
The following shows how to make a mask, offering some protection against coronavirus. The filtration medium is HEPA 10 fabric, as used in vacuum cleaner bags specifically designed for use in such places as asthmatic households. Numatic NVM-1CH filters, and others of the same specification, will absorb 85% of particles 0.5 microns across. The majority of virus carrying particles are larger than this, giving a higher overall collection efficiency.
Several medical reports suggest an N95 mask offer 5x more protection than none at all. N95 collects 95% of particles 0.3 microns across, whereas this fabric is not quite so efficient. However the wearing of a mask also prevents the user from accidentally touching mouth and nose, and is a constant reminder to avoid contact with contaminated surfaces, and wash or sterilise hands regularly.
In the description, lengths are in millimetres. Italic text shows near equivalents in inches and cm.
To print these instructions, please download the PDF version using this link, and print the PDF version.
Items needed|
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Price examples: Numatic Henry Cleaner Bags - 1 Box (Pack of 10) £7.49 Duck Tape 232318 All Purpose Masking Tape, 50 mm x 50 m. £4.32 Prices from Amazon. Makes about 30 masks. |
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The area to cut is: 220 x 110 mm (Equivalent to: 22 x 11 cm, or 8 ½ x 4 inches) |
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Mark out the area shown, with a seam along the long side. Cut out.
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Cut 2 corners approximately 20 x 60 mm (2 x 6 cm, or 1 x 2 ½ inches) |
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Open out the fabric and position it with the seam underneath and with the seam fold to the bottom.
Bend the ends of the wire into a tight loop so they so they cannot poke through the fabric.
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Cut a strip of tape 10-15 mm wide and attach the wire 8-10 mm down from the edge. (Tape width 1 to 1.5 cm or ½ inch, attached 1 cm or ½ inch down from the top edge of the mask) |
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Fold the fabric over the wire and stick down with 10-15 mm wide tape. Tape the ends with 25 mm wide tape, folding over. Trim off excess (The width of the 25 mm tape is 2.5 cm or one inch.) |
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Form a pleat 12 mm wide at the end, with a slight angle as shown. This helps to form a 3 dimensional shape to the mask. Staple. Now make a smaller pleat each side of the central one and staple. (The first pleat is ½ inch wide, or 1.2 cm.) |
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Now pleat the other end. |
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There are two easy methods of attaching ties. The elastic band method is shown here.
Cut 4 pieces of fabric 12 x 30 mm. (1.2 cm x 3 cm, or ½ inch x 1 ¼ inch)
Select 4 rubber bands, typically 1.5 mm x 100 mm. The 100 mm (= 10 cm, 4 inches) is the un-stretched length laid out straight. Thicker bands are too tight as a loop, but 3 mm wide bands can be cut so a single strand is used. However the ends are difficult to secure and need superglue to form an end loop.
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Loop 2 bands together to double the length. Fold the fabric over the band and secure with a dab of glue from a Pritt stick or contact adhesive. The fabric loop can then be stapled to the mask. Stapling the bands directly often fails as the sharp edges of the staple cut in to the rubber.
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The band is stapled to the outside of the mask, at each corner. |
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The mask is ready to try. If the bands are too tight, remove staples one side and add an extra band, as shown in the 3 band tie next to the mask. Re-staple. |
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The elastic ties fit below and above the ears. The wire should be moulded to fit snugly around the nose, so you do not feel a draught around the eyes when exhaling. |
One Henry bag makes three masks. |
A possible cut-up |
Above left: the alternative elastic tie. Use a hole punch to make a hole at each corner of the mask and tie the elastic with a simple knot. Allow extra length so the tension can be adjusted. The disadvantage is that fabric covered elastic will only stretch about twice its relaxed length and may be tight when fitting over the head, yet give insufficient pull when in position.
Above right: 30 masks from a £7.50 box of 10 bags. Each mask costs about 25p.
STERILISATION OF USED MASKS
WHO report (link below) states the virus is destroyed by a temperature of 56 Centigrade for 15 minutes. I have tested these masks, along with 3M 9332 valved masks, in an industrial fan oven, at 70 Centigrade for 20 minutes. There is no damage to any part of the mask, the rubber is unaffected and the tape remains bonded. A domestic fan oven set to 65 -70 C should achieve the same result.
Also read WHO guidance:
https://www.who.int/csr/sars/survival_2003_05_04/en/
Roger Hadland 26/03/2020
Converted to HTML by Oliver Larkin
