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DIYBIO - Integrated Hood Design

Reducing the current 3-piece headgear combination of face mask, visor/goggles, and hood to one integrated hood design. Design ideas: - full transparent visor, improving visibility for the health care worker, and rapport with the patient - lightweight and breathable - channel exhaled air out, to avoid fogging and inhalation - push fresh air in, to improve cooling, and avoid fogging and CO2 buildup This design was prototyped initially at the Fighting Ebola ideation workshop in Washington DC on Oct 10-11, by Ellen Jorgensen from Genspace, and Patrik D'haeseleer from Counter Culture Labs.

Photo of Patrik D'haeseleer
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The current head and face PPE used by health care workers from Medicins Sans Frontieres (MSF) to treat Ebola patients consists typically of three parts: a "duck bill" mask covering the nose and mouth, a set of goggles covering the remainder of the face, and a hood covering the hair, neck and throat. This tight-fitting three-piece layered system is uncomfortable to wear, overly complex (leading to mistakes during donning and doffing), limits visibility, and reduces rapport with the patients due to the lack of a visible face.

One alternative to wearing the gear described above would be to wear a full hood with a transparent face plate and a respirator (e.g. the 3M Breathe-Easy Hood). Such a system is expensive, and better suited to protecting against aerosol propagated diseases. We propose an integrated one-piece hood design that is far less complex and ideally equally affordable than the current three-piece system, borrowing some ideas from a fully enclosed hood with respirator, but without needing to provide full aerosol protection.

A standard Powered Air Purifying Respirator (PAPR) provides a filtered air flow rate of greater than 4 cfm (cubic feet per minute) for a tight fitting face-piece, while 6 cfm is necessary for a loose fitting PAPR. Under normal conditions of use, the worker is supplied with more air than he/she can breathe so that the inside of the face-piece is under positive pressure and no contaminated air can leak in.

Since Ebola is not aerosol transmitted, we do not need a full HEPA filter, or maintain strict positive pressure, meaning a much smaller and cheaper fan can be used to push air into the hood. Off-the-shelf cage fans with a diameter of 35-40mm can easily provide 6 cfm or more  against a light back pressure. Our initial prototype used a Radio Shack 12V Micro Fan, which provides 7.7 cfm and retails for $14.99, although similar models can be found online for $1.99 (newegg) or even less, allowing them to be a component of a fully disposable hood design. The fan can be powered via wires running inside the hood to a 12V rechargeable battery pack in a shirt or pant pocket. The air inlet of the fan will be covered with a splash guard to keep liquids and droplets from entering the system.

For a hood covering the entire head, it is important to channel exhaled air away from the face plate to avoid fogging. In our initial prototype, we used a silicone nose+mouth cup borrowed from a different PPE piece (a  3M Ultimate FX Full Facepiece Respirator), with one-way valves that allowed air to come in from the sides on the inhale, and another one-way valve that pushed exhaled out at the mouth. This silicone cup was attached directly to the face plate of the hood, so the whole thing could be donned and doffed as a single piece.

This arrangement worked well functionally, but is overkill and still hides much of the face. In order to channel exhaled air away from the face plate, it should be sufficient to provide a strip of open-cell foam directly attached in an inverted V to a full transparent face shield, separating the nose and mouth compartment from the rest of the hood. The open-cell foam will allow fresh air to be sucked in from the rest of the hood, while a one-way valve at the chin allows exhaled moist air to exit the hood. 

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