COVID-19 Protection Halfmask BUT-H1

A team of Brno University of Technology researchers and students have developed a 3D printable protection half mask that does not require a special material or printer. The product is intended for the general public and can be easily manufactured on regular 3D equipment utilizing the FDM technology (thermoplastic modeling). Although such printers are usually not recommended for such purposes due to the eventual porosity and difficult sealing of the product, the BUT team’s concept involves an original solution to this problem, allowing the use of standard devices.

The BUT-H1 half mask features a very simple structure, comprising:

• a frame (3D printable)
• filter holder (3D printable);
• a disposable glove-based sleeve (latex or nitril);
• an improvised filtering insert (such as a vacuum cleaner HEPA filter or bag, or an air cleaner filter);
• headstraps;
• thin kitchen rubber bands.

NEWS

• Our new contact e-mail address for questions regarding our mask is vutmaska@gmail.com.
• The first major testing of the mask is currently underway. Many volunteers print the mask. We would like to thank all of them for their trust.
• If you have printed the mask, please, share your experience regarding the functionality and ergonomics/comfort with us!
• We analyze all comments, we react to them and we continually upgrade the design. We make new versions of models available for download as soon as they are ready.
• In the "Manufacturing Files" section, the date of the issue is shown for each model.
• Testing of the filtration efficiency of some well defined and broadly available filter materials is ongoing. We will inform about its results soon.

User benefits

Compared to a simple 3D-printed version, this original product including a sleeve brings the following advantages:

• Multiple sizes available
• Full sealing thanks to the applied glove
• Good face shape adaptability, meaning optimal tightness
• Face skin contact only with the actual material of the disposable glove
• A sleeve-protected structure eliminating external contamination completely
• A sleeve quick and cheap to replace or disinfect.

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Basic information

The protection provided by a half mask, surgical mask, or respirator depends mainly on a tight face fit; the filtering capability of the applied medium is only a secondary parameter. Even improvised filtering instruments substantially reduce the virus contraction risk, although their protective performance cannot match that of a classic tool.

This product is intended for non-professional use, replacing regular surgical masks and respirators when these are unavailable or do not fit on tightly due to improper design or heavy everyday duty. Our half mask does not comprise an expiratory valve, and the humidity aggregates in the filtering medium; similarly to surgical masks, there then forms a potentially bacterial environment, meaning that the filter must be dried and disinfected or discarded.

Components

To fabricate the halfmask, the following items are necessary:

• A 3D printer capable of delivering a product with the dimensions of 13 x 13 x 7 cm; most standard devices will meet the criterion
• Printing material (filament); generally, the requirements are very minimal, and the user can employ PLA, ABS, PET, PET-G, ASA, CPE, or any relevant alternative
• An elastic, disposable, L-sized glove; other sizes may find application too, although L embodies the ideal option. Nitril gloves are recommended thanks to their durability and overall strength; a latex sleeve is also convenient but offers less reliability and must not be used by persons allergic to the substance. Condoms are also usable if necessary
• An improvised filtering insert having a square-shaped size of at least 70 x 70 mm
• Strings, elastic rubber bands, or other material to form the headstraps
• Two thin rubber ribbons (cut out from, for example, an inner tube for bicycle wheels)
• A pair of scissors.

Mask shape adjustment

With many printing materials there is a possibility to perform small shape corrections in order to achieve good fit. In general, only the width of the mask can be adapted successfully. Therefore since the beginning the mask must suit the user in length, i.e. choosing the right size for printing is essential.

To adjust the shape (width), please follow the steps below:

• Find out at what temperature the printing material starts to become becomes plastic (In the case of PLA, it starts to soften at 60 ° C).
• Heat about half a liter of water to this temperature (approximately). Do not use temperatures that might cause skin burns quickly!
• To prevent dangerous skin burns of sensitive children's skin, do not use this procedure for children's masks.
• Immerse approx. 1/3 of the face part of the mask in the water and allow it the mask to warm up for a few seconds. Attention! Do not fully submerge the whole mask as there is a risk of deformation of the front with the filter contact surface!
• Remove the mask from the water and try to gently adjust its shape to fit the face better.
• If needed, repeat the procedure. Be careful not to overheat the mask as the mask would be deformed.

Assembly steps

After the printing, the actual half mask body, or frame, and the filter holder both have to be refined by quickly rubbing off (with a knife or sandpaper, for instance) any sharp protrusions or edges that could damage the glove. Subsequently, the selected glove is put on the body and then cut and adjusted conveniently to wrap around the body, forming a tunnel-shaped section.

With the glove already on, a couple of thin rubber ribbons will now have to be inserted in the grooves milled in the body (frame); these ribbons will firmly lock the two structural components of the half mask together.

To obtain the improvised filter, the user can employ materials applied in surgical masks, home air cleaner filters, and similar items. Several different materials can be combined for the purpose, depending only on their air permeability to allow comfortable breathing. The shape of the filter is easy to capture with the guide element (template), which enables the user to quickly copy the lines before trimming the desired medium.

At the next stages, the filter is inserted in the holder, and the holder is attached to the frame. The rubber ribbons at the edge of the frame should ensure firm connection between the two structural parts; the number of ribbons used must be adjusted to their thicknesses.

The headstraps consist in strings or elastic rubber bands sewn or tied to the holder, and their lengths are set to fit the person.

Disinfecting the surfaces

• Filter: Ideally, the filter should be heat-treated (by using tools such as a flatiron) or replaced with a new one; the procedure has to be chosen according to the printing material used
• Filter Holder: Immerse the holder in a disinfecting solution (for example, ethanol, isopropylalcohol, or Savo Original diluted at the rate of 1:6); the applicability of a solution depends on the printing material utilized.
• Sleeve: The glove is either treated with a disinfecting solution or replaced with a new item.
• Structural Parts: The body of the halfmask can be immersed in a suitable solution (such as ethanol, isopropylalcohol, or Savo Original diluted at the rate of 1:6); surface-wiped with a disinfectant; or washed in soap water. Under normal conditions and standard use, contamination by the external environment is not assumed, and soap water washing thus appears to be fully sufficient.

Manufacturing files

• Half-mask frame (size L, size M, size S) (4/2/2020)
• Filter Cover (for thin filters < 3mm, for thick filters > 3 mm) (4/2/2020)
• Filter shaper (template) (4/3/2020)
• User and assembly manual (4/2/2020)

The set of manufacturing files is currently being expanded, with other half mask sizes added; the materials will be released within several hours.

The Team

Industrial Automation Group

Department of Control and Measurement, Faculty of Electrical Engineering and Communication, Brno University of Technology

• Contact e-mail address: vutmaska@gmail.com
• Václav Kaczmarczyk
• Ondřej Baštán
• Michal Husák
• Petr Fiedler.
• Zdeněk Bradáč

Gallery

Acknowledgement

The research team thank in particular the Siemens corporation for its long-term collaborative efforts and assistance within 3D modeling and software application, and
the Speltronic company for the materials and information made available.

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