Static Electricity

What are you doing for "grounding"?

You might want to look into the subject of ESD (Electro-Static Discharge) and the mechanisms used to control it.

You may what to call EXAIR.

They do make static eliminators for sheet plastic. I didn't look through it, but they may also have something for your application.

This is not unlike what happens when you slide across your seat in the wintertime and get shocked.

When two non-conductive surfaces, or particles in this case, come into contact and then have that contact broken, a static charge is generated. The patient's lips, being conductive, then bleed the charge directly into the patient.

Simply having the patient hold the device for a few moments prior to use might bring both the inhaler and patient to the same electrical potential.

Static eliminators contain a small amount of radioactive material. That may have implications in a hospital.

If possible, increasing the humidity in the room may solve this problem, too.

On shag carpet in the dead of winter? :)

Like I said before, reading up on ESD and the methods to mitigate it will help.

However, you probably need to hire or contract someone who is an expert in the field since this is a public health situation. There are lawyers everywhere and if it was found you were relying on ad-hoc methods to solve a problem it could backfire legally.

Wood will isolate the patient. Metal would bleed the ESD away, but perhaps too rapidly.

I am thinking they will need an ESD mat on the floor or ESD tiles and some sort of grounding station that the patient would grab or touch as part of the process to bleed off ESD in a slow and controlled way (so as to not feel a shock).

Each human has a different capacitance. If it is the same people, have them try a wrist type ground strap.

Though the solids in this device are most likely producing some charge. The rate of charge would depend on how fast. If they where moving that fast I would think the the procedure would be very uncomfortable to the patient.

I would look at each patient. The static may be in them. Look at their foot wear. Wool slippers would create static. Also how they walk do they shuffle their feet dragging them on the ground. The material of the clothes these few people wear. Do these people have dry skin. Dry skin can offer the highest resistance to current. Until you get it wet.

When I was in training for fuel handling equipment we were shown videos (old ones) of dry air flowing through pipes. The voice-over described how microscopic dust particles in the dry fluid (air) can generate static charge in the pipe. They used this principal to detonate balloons filled with flameable gasses.

Your dry powder increases the contact between the particles and the pipe generating the charge. As others have said there are many properties that govern any person's electrostatic potential; clothing, body composition, humidity, shoes etc.

Look for a way of making your equipment conductive either through a surface coating or through plastic composition. Have the patient wear a static discharge bracelet and equalize the potential between them and the equipment and you should eliminate the chance of a spark when they contact the equipment. The bracelets will discharge any potential at the wrist where there are fewer nerve endings to feel any shock as it is equalized over a larger surface area.

Drew K

Lots of good suggestions given by others. Just in case you "don't see the light" I'll summarize in simplistic terms.

1) Low humidity tends to cause ESD (Electro Static Discharge) problems. Higher humidity might reduce buildup of charge. Due to humidity ESD tends to be worse in the winter.

2) ESD problems are the build up of static charges and then the RAPID discharge of the static charge. The "ESD wrist strap" suggestion by others would cause a slow and constant discharge of ESD. ESD wrist straps are common in electronics assembly and repair facilities.

3) Some materials generate static charge when rubbed together. Remember first grade science where the teacher ripped paper into small pieces and used a hair comb to pick up the paper? Any material combinations that act like "rubber and wool" or "silk and glass" from first grade will tend to cause more static charge build up. Thus, cotton clothing will tend to cause less buildup of charge and synthetics, silk and fuzzy sweaters will tend to cause more buildup of static charge.

4) Grounding equipment or causing plastic surfaces to be conductive might cause all static to quickly flow (before buildup, not a large discharge) to ground but you might be very limited to what you could try from both a practical point of view and a liability point of view.

5) You must be responsible for safety and legal issues if you read this comment. When it is difficult to figure out how to make something better then sometimes it is useful to figure out how to make it worse. Then, you have a better understanding of what it is that you don't want to do. If you can safely and legally do it consider testing the equipment in a walk-in freezer with a person wearing synthetic clothing and a fuzzy sweater on a plastic chair on top of a shag carpet rug. If you notice the problem being worse then you can change things one at a time and learn something. Remember, I said "might" and "maybe". Also, safety and legality are your responsibility.

6) The hood manufacturer and nebulizer manufacturer might not have much of an interest in calls about an annoyance of shocks or sparks. Chances are your response would be better with a call of concern about the safety of patients with pacemakers or other health compromising conditions.

7) It is always good for your career to remember that a common technique for management to clear their desk of problems is to shoot the messenger.

The fact that you are breaking a liquid into an aerosol will generate static electricity; similar to unwinding scotch tape in a dry environment. This means that anything the spray hits will become charged, unless it is grounded There are many methods to mitigate the effects of the static electricity, but the most direct method is to use an ionizing loop at the aerosol exit.