design_for_dust

DESIGN

APRIL 2008

47

TEST & MEASUREMENT WORLD  www.tmworld.com

Just because you work in an air-condi-

tioned office or a temperature-con-
trolled lab and breathe filtered air 
doesn’t mean your equipment won’t 
suffer from indoor air pollution. Dust 
and moisture still accumulate on 

printed-circuit boards (PCBs) inside product en-
closures, increasing the chance of an electrical 
breakdown (arc-over) between circuits. Electrical 
breakdown can put users at shock risk or can result 
in a product fire. To guard against the negative ef-
fects of airborne pollution, you must design prod-
ucts to meet insulation requirements. 

Air is a mixture of nitrogen, oxygen, carbon di-

oxide, argon, and trace gases. When you add dust 
(particulate matter) and water (vapor), you get in-
door air pollution. Studies from state and federal 
environmental agencies show that indoor pollution 
levels can sometimes range between two and five 
times higher than outdoor levels (Refs. 1, 2).

Most indoor dust pollution comes from build-

ing materials such as airborne fiberglass, partition 

fibers, and carpets as well as office machines, copi-
ers, and smoke. The insides of computers in service 
for only a few months can often be coated with 
layers of dust, which can cause electrical shorts 
(Figure 1). Metallic dust particles present in in-
dustrial environments cause more trouble because 
they’re more conductive than typical office dust. 
Conductive dust sources include motors, paper 
shredders, conveyors, and manufacturing and con-
struction processes. Electronic equipment manu-
facturers often suggest cleaning internal PCBs and 
air filters in products to prevent dust buildup.

Water pollution also raises safety risks. Water vapor 

can come from many sources including cleaning 
products, air conditioners, water coolers, carpets, and 
fumes, and from the heating of food and beverages. 
Your breath contains hundreds of drops of water 
vapor, which you can see form when you breathe 
on a cold pair of eyeglasses. One person’s breathing 
can produce 1⁄4 cup of water per hour.

Condensation coats the surface of electrical cir-

cuitry and can saturate dust coatings. Moisture can 

BY DAVID LOHBECK, NATIONAL INSTRUMENTS

PRODUCT SAFETY

for

DUST AND WATER VAPOR on electronic components 

can pose risks to product users, so design your products to 

resist the shorts and shocks that can result from buildup.

PRODUCT SAFETY

increase conductivity between electrical 
circuits, which can cause short circuits 
resulting in product damage, fire, or elec-
trical shock (Ref. 3).

Safety standards address 
pollutionAlthough modern buildings use air-filtra-
tion systems, dust and water will still build 
up over time. Product safety standards take 
air pollution into account, and by design-
ing your product to comply with these 
standards, you will minimize safety risks.