Hand Hygiene

I met with Ted and Phil for several hours yesterday to organize and focus this project a bit more, given that the financial resources have settled down a bit.  The primary conclusion was that we need to shine a laser-like focus on the acquisition of a clear signal in the hand sanitizer application.  We’re also going to get a copy of the software that they are using in the hospital to use in the lab, so we can validate that our mockup tests are consistent with the output of the software.  A major difference between our tests and the software is that the software only takes one measurement every 7 seconds, whereas most of our test software takes a measurement 4 times a seconds.  However, the hospital software has many critical features that we aren’t using for the hardware development, like synchronizing clocks for periodic messaging and power-saving capabilities.

We decided that the target for the hardware should be the absolute determination of who activated the hand sanitizer.  The shoulder-grip length of a 95% male is 715 mm.  That’s the distance from their shoulder to the middle of their hand with the arm extended directly.  The 95% male forward grip reach is 835 mm.  That’s the distance from the back of the shoulder to the grip point with the arm fully extended. Since the back of the shoulder is approximately equal to the position of the back of the hip, that’s a reasonable maximum distance for using the hand sanitizer, although it is not completely precise, because someone could conceivably stoop forward and extend his or her hand out to reach the sanitizer, but that would be a very awkward posture. 

The minimum distance would be something similar to the forearm to fingertip length.  For the 5% female, this distance is 400 mm.  Subtracting distance for the front of the hip and the length of the hand might make this about 360 mm. 

Thus the hand hygiene sanitizer must be able to determine whether a person is between 360mm and 835 mm of the unit when it is activated.  Since it is unlike someone will be closer to the unit than the person using it, we could reasonably say that it must provide a detectable signal to a distance of 835 mm from the unit.  After further discussion, we realized that this is an unrealistic constraint, since it doesn’t really specify two conditions that the mote must distinguish between.  Since the target is 835 mm, let us say that we’ll try to distinguish between .75 and 1.0m.

Assume that the device is mounted on a wall and the person will be within 90 degrees directly in front of the device.

Of course the device may not be 100% accurate.  For the sake of argument, let’s assume that it is accurate 95% of the time.

The device must maintain this reliability whether or not the person is wearing the pager on the front of their belt or the back.

There is probably some minimum length of time that we must assume that the person stands in front of the device to wash their hands, but I don’t know this.

There is a vertical offset between the pager mote and the mote in the dispenser.  For the hand pump, the recommended height of the mount is 1.1 m above the floor.  The hip height for a 5% woman is 740 mm and for a 95% male it is 1000mm.  Therefore we’ll assume that the pager motes should be 0.1 to 0.35 m below the bottom of the hand pump dispenser.

We should add constraints as we figure them out.