NAVAIR 01-1A-509-3
01 March 2005
TM 1-1500-344-23-3
TO 1-1-689-3
8-3.3. HUMAN BODY GENERATED ESD. People are
p r i m e sources of ESD that damage avionic
More POSITIVELY Charged
components. Electrostatic charges generated by
Air
rubbing or separating materials are readily transmitted
Human Hands
to a person's conductive layer. This causes that person
Asbestos
t o be electrostatically charged. When an
Rabbit Fur
electrostatically charged person handles or comes
Glass
near an ESDS part, he can damage it from direct
Mica
discharge. The change in voltage of a human body
Human Hair
Nylon
with normal maintenance activities is shown in
Wool
Figure 8-2. In addition to accumulating electrostatic
Fur
charges, the human body can retain electrostatic
Lead
potential over time. An example of this is a low relative
Silk
humidity, it may take a human form more than one hour
Aluminum
to bleed off 400V potential. A graph that contrasts
Paper
electrostatic potential with bleed-off time is outlined in
Cotton
Steel
Figure 8-3 for Teflon and concrete floors. This general
Wood
trend highlights the need for using ESD control devices,
Amber
particularly in repair shops where relative humidity is
Sealing Wax
low.
Hard Rubber
Nickel Copper
8-3.4. PRIME SOURCES OF STATIC CHARGE.
Brass Silver
Gold Platinum
Some items create or maintain charges better than
Acetate Rayon
others. This is because some materials readily give up
Polyester
electrons while others tend to accumulate excess
Orlon
electrons. An item having an excess of electrons is
Saran
negatively charged while an item having an electron
Polyurethane
deficit is positively charged. When two materials are
Polyethylene
Polypropylene
rubbed together, then separated, one material gains
PVC (Vinyl)
electrons and the other loses electrons. This also
Silicon
occurs when materials flow relative to one another,
Teflon
such as gas or liquid over a solid. These electron
charges are equal, and in the case of nonconductors
More NEGATIVELY Charged
tend to remain in the localized area of contact. Charges
on conductors, however, are rapidly distributed over
Figure 8-1. Triboelectric Series (Partial)
its surface and the surfaces of other conductive objects
it contacts. These items can be considered as typical
A partial triboelectric series is outlined in Figure 8-1.
prime charge sources. Prime sources are essentially
Materials that are further apart on the table generate
insulators and are typically synthetic. Table 8-1 lists
the greatest static charge when rubbed together. This
typical prime charge sources. Electrostatic charge on
occurs with the materials nearest to the top of the table
these items may be extremely high, as the charge is
retaining the positive change. An example of this is the
localized and is not distributed over the entire surface.
motion of air against synthetics generates the highest
This charge could be reduced in high humidity
static charge. Also, rubbing polyethylene and human
environments, as this allows more conduction/
hair will generate a greater static charge than the
distribution of the charge. Table 8-2 lists typical
charge resulting from rubbing nylon and cotton. Another
electrostatic charges generated by personnel in a
possible explanation of charge accumulation between
repair facility.
two bodies is that ion transfer between surfaces causes
static charge buildup. Other possible causes of electron
8-3.5. S P E C I A L CONSIDERATIONS. Many
t r a n s f e r between contacting surfaces include
microelectronic circuit repair facilities include clean
differences in dielectric constant, thermal effects, and
room conditions. These conditions are designed to
piezoelectric or pressure effects.
maintain the absence of dust and other particles in the
maintenance environment. Materials used in this
