Transcript Slide 1 - Faculty

ENTC 4350
Electrical Safety

Hospital electrical safety begins with the
principles that we have discussed.
• An electrical shock is always unpleasant, but
it can be lethal in the intensive care unit.

It is extremely important that all hospital
personnel be constantly on the watch for
manufacturing defects or wear and tear of
critical parts.
•
•
•
There are documented cases where equipment from
reputable manufacturers was delivered with ground
wires disconnected, cords broken, and improperly
installed plugs.
In the meantime, there is still the patient; it is your
patient and your responsibility.
You are the one who must be suspicious and check
the equipment when it comes from the factory.

Even if equipment is in perfect condition
when it arrives from the manufacturer, it
is subject to the normal wear and tear of
daily hospital use.
• This type of deterioration may be very severe
if the equipment is dragged around, in a great
rush, from one room to another in response to
emergencies.
• Once again, the part of the system that is most
likely to be damaged is the cord and plug
assembly.

Quite often, the damage is not visible on a
mere surface examination; you have to get out
your VOM or continuity tester and test it.
•
Connect the continuity tester or VOM between the
ground plug on the end of the cord and the metal case
of the instrument.
• If the test light goes out when you wiggle or pull on the
•
wire, or
If the resistance measured by the VOM is erratic when
you move the cord, then the appliance is defective.

If your hospital has a red tag service that
allows defective equipment to be marked
for immediate pickup and repair, all is
well.
• However, if there is any danger that the
equipment might be used in patient service
before the repair is done, the best thing to do
is take your handy bandage scissors and cut
the plug off.
• That may sound like a drastic measure (surgery is
always drastic), but in this case, it is quite justified.

Another thing to watch for is someone
else’s ‘home repair.”
• This is particularly apparent in hospitals
•
where one sees cracked cords or broken
plugs repaired with adhesive tape.
That cord or plug cracked for a reason:
• either age or
• misuse is usually to blame.

If the insulation is cracked, most of the
conducting wires may be broken, too.
• Just suppose that the last strand of ground
wire broke when it was being used on your
patient, and reflect upon the results of our
computations with the current divider
equations previously.

In this regard, you have to watch the other staff
members—i.e., the orderlies, aides, and so
on—since the natural human tendency is to put
the broken item back on the shelf and take one
that looks all right.
•
•
Quite often, an aide will hesitate to report defective
equipment for fear of being thought to be a
troublemaker.
Only endless repetition, and possibly a cash prize for
reporting defects, will alleviate this situation.

It should he clear to everyone that if any
defective equipment is noted, or if a
tingle is sometimes felt when using a
piece of equipment, this is a signal to
stop using the equipment and report it.

The patient is truly at your mercy, and
equipment that comes near to him or her must
be in proper condition.
•
•
At this point, you might be wondering just what proper
condition is and how leakage occurs.
The specifications on electrical leakage are complex
and subject to change; however, two good points to
keep in mind are the leakage to the chassis of hospital
equipment and the leakage through any patientconnected leads.

With the ground wire disconnected, the chassis
leakage is limited to 100 mA, and the patientlead leakage must not exceed 50 mA.
•
There are many causes for leakage:
• defective insulators,
• damaged wire,
• dirt,
• water, and
• the radiation leakage.
"Electric
Shock,"
Advances in
Biomedical
Engineering,
edited by J.
H. U. Brown
and J. F.
Dickson IIII,
1973, 3, 223248.)
Figure 14.1 Physiological effects of electricity Threshold or estimated mean values are
given for each effect in a 70 kg human for a 1 to 3 s exposure to 60 Hz current applied via
copper wires grasped by the hands.
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

They all add up to a problem for the
hospital.

The danger of having a single hospital appliance
with a defective three-wire cord is illustrated below.
•
Here we show a patient in an electrical bed with a threewire cord that is good.

This means that when the patient puts his
hand on the bed rail, he is grounded. too.
•
There is nothing wrong with that until someone brings
over a second appliance, like an ECG or an apnea
monitor, which has a defective three-wire cord.
• The manufacturer designed the appliance with the idea
•
that the three-wire cord would be operational and that
stray leakage in his unit would be grounded off to the
case and removed by the ground wire.
Unfortunately. in this case, the third wire is broken, and
the leakage current goes back to the powerhouse via
the patient with disastrous results.

Every time you wheel a piece of
electrical equipment up to a patient, you
have to ask yourself,
• “Am I sure that the ground wire is OK?”
Figure 14.5 Effect of entry points on current distribution (a) Macroshock, externally
applied current spreads throughout the body. (b) Microshock, all the current applied through
an intracardiac catheter flows through the heart. (From F. J. Weibell, "Electrical Safety in the
Hospital," Annals of Biomedical Engineering, 1974, 2, 126-148.)
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
UNDERWRITERS’
LABORATORIES
STANDARDS

There have been some gaps in the
design of medical equipment, but these
holes will be closed as more hospitals
require that all new equipment meet the
Underwriters’ Laboratories Standards for
Medical and Dental Equipment (UL 544).
• The important thing about UL 544 is its
marking code for guidance in equipment
application.

Type A apparatus, the highest grade, is
suitable for electrically susceptible
patients.
• This means that the leakage current has been
held to the lowest possible value, and the
greatest measure of safety has been provided
for patients in intensive care, cardiac care, or
catheterization units.

Type A equipment is very costly, and for
this reason, a somewhat lower standard
is used for type B, which applies to
equipment not suitable for electrically
susceptible patients.
• This equipment is not defective or poorly built.
• The designation is simply a recognition that the
precautions needed in the CCU, for example, are
not appropriate for the general medical patient.

The last, or type C, equipment label is
intended for laboratory apparatus where
patient contact is unlikely.
• In some cases, no marking will be used on
type C equipment, but the hospital may want
to have stickers saying not for use outside the
laboratory area or not for use on patients.
• The UL 544 code designation is one more item to
be checked when new apparatus is brought in for
patient use.
Regulation of Medical Devices

In 1976, the U.S. Congress passed what
are known as the Medical Device
Amendments (Public Law 94-295) to the
Federal Food, Drug, and Cosmetics Act.
• Further amendments were made in 1990 in
the Safe Medical Devices Act.

Medical devices are defined as:
• any item promoted for a medical purpose that
does not rely on chemical action to achieve its
intended effect.

Medical devices are classified in two
ways:
1. The division of such devices into Class I,
Class II, and Class III.
•
Based upon the principle that devices that pose
greater hazards should be subject to more
regulatory requirements.
2. Seven categories
•
•
•
•
•
•
•
Preamendment,
Postamendment,
Substantially equivalent,
Implant,
Custom,
Investigational, and
Transitional.

Software used in medical devices has
become an area of increasing concern.
• Several serious accidents have been traced
to software bugs.
• Increased requirements for maintaining traceability
of devices to the ultimate customer, postmarketing
surveillance for life-sustaining and life-supporting
implants, and hospital reporting requirements for
adverse incidents were added to the law in 1990.
Class I: General Controls

Manufacturers are required to perform
registration, premarketing notification,
record keeping, labeling, reporting of
adverse experiences, and good
manufacturing practices.
• Apply to all three classes.
Class II: Performance
Standards

These standards were to be defined by
the federal government, but the
complexity of procedures called for and
the enormity of the task have resulted in
little progress having been made toward
defining 800 standards needed.
• The result has been overreliance on the
postamendment “substantial equivalence”
known as the 510(k)process.
Class III: Premarketing
Approval

Such approval is required for devices
used in supporting or sustaining human
life and preventing impairment of human
health.
• The FDA has extensively regulated these
devices by requiring manufacturers to prove
their safety and effectiveness prior to market
release.
WALL RECEPTACLES

There are times when it is important for you to
be able to find the neutral, hot, and ground
jacks of the wall receptacles or outlets.
•
•
Suppose. for example. that you move into a new (or
new to you) facility with three-wire grounded
receptacles.
All is well until you begin worrying that the contractor
might have forgotten to hook up the ground wire at
some ot the receptacles.
• It has been our experience that many contractors do not
install the receptacles correctly.
Figure 14.6 Simplified electric-power distribution for 115 V circuits. Power frequency is 60 Hz.
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

The protection that you think you have is
not there, and you might not want to find
that out the hard way.
• When the hospital is new, the contractor will
fix a little thing like this when the building is 10
years old, however, he may be somewhat
hard to find.

We suggest that when you move into a
facility, you whip out your VOM or outlet
tester and check the receptacles.
• A typical outlet tester is shown below.
Figure 14.16 Three-LED receptacle tester Ordinary silicon diodes prevent damaging
reverse-LED currents, and resistors limit current. The LEDs are ON for line voltages from
about 20 V rms to greater than 240 V rms, so these devices should not be used to measure
line voltage.
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

Its dimensions are those of a large spool of
thread.
•
These gadgets are not perfect: a poor ground—i .e..
one with high resistance—might check out all right,
because the neon bulbs inside the tester only require
a small current to light up (a neon bulb operating at 65
volts and 0.25 watt will light up even when the ground
resistance is as high as 13,000 ohms).
• However, that is no excuse to avoid using a gadget of
this type, because something is always better than
nothing.

A better method for checking the wall
receptacles involves the use of your
VOM.



The right-hand
opening should be
‘hot,”
The left should be
“neutral,” and
The other opening
should be “ground”
Figure 14.18 (a) Chassis
leakage-current test. (b) Current
–meter circuit to be used for
measuring leakage current. It
has an input impedance of 1 k
and a frequency characteristic
that is flat to 1 kHz, drops at the
rate of 20 dB/decade to 100 kHz,
and then remains flat to 1 MHz
or higher. (Reprinted with
permission from NFPA 99-1996,
"Health Care Facilities,"
Copyright © 1996, National Fire
Protection Association, Quincy,
MA 02269. This reprinted
material is not the complete and
official position of the National
Fire Protection Association, on
the referenced subject, which is
represented only by the standard
in its entirety.)
Appliance power switch
(use both OFF and ON positions)
Open switch
for appliances
not intended to
contact a patient
Grounding-contact
switch (use in
OPEN position)
Polarity- reversing
switch (use both
positions)
Appliance
H (black)
To exposed conductive
surface or if none, then 10 by
20 cm metal foil in contact
with the exposed surface
H
N
120 V
N (white)
G (green)
Building
ground
G
Insulating surface
I
Current meter
This connection
is at service
entrance or on
supply side of
separately derived
system
H = hot
N = neutral (grounded)
G = grounding conductor
Test circuit
I < 500 A for facility Ðowned housekeeping and maintenance appliances
I > 300 A for appliances intended for use in the patient vicinity
(a)
900 
Input of
test load
1400 
0.10 F
100 
15 
mV
Millivoltmeter
Leakage current
being measured
(b)
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
Figure 14.17 Ground-pin-to-chassis resistance test
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

Any hospital that hopes to avoid lawsuits
should have a regular program for
checking the outlets.
• One
of the things that we have found to be
important is the periodic testing of the actual
resistance of the hospitals ground circuit.
• This
requires a special electrical gadget that the
Maintenance Department will have to buy and use
regularly.

Another good rule requires the
replacement of all cracked receptacles,
even when they test out “OK.”
• A cracked receptacle is like high blood
pressure; it is a signal for you to do something
about it or expect to pay the penalty.
ELECTRICAL BEDS
THE ELECTRICAL BED

Electrical beds are great gadgets; they
have saved thousands of nurses millions
of hours of cranking up and down.
• Like most gadgets, however, they have their
•
bad aspects.
A patient in a standard hospital bed on the
usual rubber tiled floor is effectively “floating”
in the electrical sense.
• The term floating simply means that he or she is
not electricaIy connected to the ground.

The conventional electrical bed has its frame
and motor case connected to electrical ground
via a three-wire cord.
•
•
This could be hazardous if the patient came in contact
with an appliance that had an electrical ‘leak” while he
was touching a grounded, metal bed rail.
To avoid this hazard, manufacturers have introduced a
variety of systems ranging from insulated bed rails to
doubly insulated motors.
Three points to keep in mind
are:
1.
Bed-related injuries to patients, such as
falls and shock, are the leading cause of
patient and visitor trauma.

Such injuries outnumber, by a factor of five,
any other type of in-hospital injury.
2.
The conventional electrical bed has its frame
and motor case connected to electrical
ground via a three-wire cord.
•
•
One hand on the grounded bed rail and the other on
a defective bed lamp can be a formula for disaster.
Other problems can occur if any conductive liquids,
such as water, blood, or urine, spill on the bed and
leak through to the motor.
•
This might allow current to flow from the motor to the
patient via the grounded bed rail.
3.
If the bed rails are ungrounded or are
not connected to the grounded frame,
the above hazards might be alleviated
but you had better check this with your
handy VOM to make sure no electrical
path exists.
•
Ungrounded bed components, however, can
act as antennas and pick up signals that
interfere with in-bed ECG or EEG studies.

A doubly insulated system has the usual
layers of functional insulation in the
motor.
• In addition, the motor itself is isolated from the
bed frame by a layer of insulating material.
• Mechanical power is transmitted from the motor to
the bed via a nonconductive coupling.

This does provide an added measure of
safety, provided we recognize that even
the best insulation will lose its insulating
qualities if it gets dirty, wet, or both.
• Dirt holds moisture, and the combination of
dust and water, blood, or urine could be a
pretty good conductor.
The Double Insulation System

The doubly insulated system can be purchased
with several different arrangements:
•
Double insulated with the motor electrically isolated
from the bed frame.
1. If there is a two-wire cord, the bed and the motor are
“floating” in the electrical sense.
2. Double insulated with a three-wire cord that grounds the
motor but not the bed, because the motor is electrically
isolated from the bed.
• Here again, the bed is “floating” rather than grounded.
3. Double insulated with a three-wire cord that grounds the
bed and the motor. In this case, the bed is grounded.
The Use of Isolated Power

To appreciate isolation, we have to
introduce a new electrical gadget: the
transformer.
• A transformer has two coils of wire;
• One is called the primary, and
• The other the secondary coil.

When an AC voltage is applied to the
primary coil, a voltage appears at the
secondary coil.
• The important point here is that the transfer of
power from the primary to the secondary
occurs without any physical connection, such
as a wire, between the two coils.
• All transfer occurs by means of electromagnetic
waves.

The circuit diagram for a transformer is
shown below.
• Note the primary and secondary coils and the
input and output voltages.

A transformer for an isolated electrical
bed has the dimensions of a cube about
one foot on each side and weighs about
50 pounds.
• The important thing to note in the figure is that
there is no voltage between either output “A”
or output B” and ground.

This can provide an important measure
of patient protection;
• For example, if the bed is grounded and the
•
patient puts one hand on the bed rail, he or
she will be grounded, too,
If something should go wrong with the bed
and if either wire A or wire B should touch the
patient, there would be no chance of injury,
because there is no voltage between either A
or B and ground.
Figure 14.7 Power-isolation-transformer system with a line-isolation monitor to detect
ground faults.
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

The next question might be, “Which one
is best?”
• Our choice might be 1 or 2 above, because
the “floating” bed provides an added measure
of patient protection.
• However, it may well be that NFPA will stick to their
ruling that all beds must be grounded, in which
case you may as well purchase the third type and
save money.

If the patient, or anyone else, touches
hot wire A and wire B at the same time,
however, they have just grabbed 115
volts.
• To
maintain isolation of power, it is most
important that neither wire A nor B touch the
bed or patient, because once contact is made
with one wire, the next accidental contact with
the other wire could be fatal.

It thus is a system that gives you one error for
free, in that contact of either wire A or wire B
with the patient does not produce any shock,
but, if one wire remains in contact, it sets
things up so that when the other wire makes
contact, zap.
•
•
Notice that this may also occur if wire A or B contacts
any grounded object.
Once the isolated power system is grounded, all
protection is lost and the next contact will have serious
consequences.
The Use of Ground Fault Detectors
and Ground Fault Interrupters

The consequences of loss of isolation are so
serious that most isolated beds will provide
either a ground fault detector (GFD) to signal
when a loss of isolation occurs or a ground
fault interrupter (GFI) to shut off the power if
the isolation is lost.
•
Most isolated power systems for electrical beds use
the GFI, because it does not require that a nurse or
aide be present to notice something is wrong and
manually disconnect the circuit.

Both the GFD and GFI operate by
comparing the current in one line with
that in the other line.
Figure 14.13 Ground-fault
circuit interrupters (a) Schematic
diagram of a solid-state GFCI
(three wire, two pole, 6 mA). (b)
Ground-fault current versus trip
time for a GFCI. [Part (a) is from
C. F. Dalziel, "Electric Shock,"
Advances in Biomedical
Engineering, edited by J. H. U.
Brown and J. F. Dickson IIII, 1973,
3, 223-248.)
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
Under normal conditions, current flowing to
the load is equal to current returning from the
load.
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
• The current flowing toward the load is exactly equal
to the current returning from the load.
– Current in both directions is made to pass through the
center of a detection coil (L1).
– Current passing through the detector coil produces a
voltage at the output terminals of the coil, but because the
outbound and inbound current is exactly equal and
opposite, the two currents together exactly cancel and
produce no output voltage from the detector coil.
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
• The differential current is sensed by the upper
coil (green).
– The lower coil injects a signal into both conductors
to detect a grounded neutral.
– The "hot" wire is the insulated conductor shown
passing vertically through both coils, and the
"neutral" wire is the bare wire.
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
• The coils are wound on a torroidal (donut-shaped)
core made of a material called "ferrite", which is an
efficient conductor of magnetic flux.
– The arrangement, along with the many turns of wire wound
around the core, is called a torroidal transformer.
– The very large number of turns produces a useful detection
voltage from the magnetic field of the line conductors
passing through the center.
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
When a ground fault occurs, part of the
current returns via the ground path.
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
• When some fault in the insulation of the
conductors or the appliance, or accidental contact
with a person causes leakage of current to ground,
that part of the current does not flow in the
intended path, so the current in one conductor
does not quite equal the current in the other.
– In this condition, the magnetic fields of the hot and
neutral conductors do not exactly cancel, and the
detection coil produces a voltage.
– The ground fault detector circuit senses the voltage
from the detection coil and sends a pulse of current
through the trip solenoid.
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
When the GFI is tripped, the load contacts
open to stop all current.
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
• The solenoid unlatches the interrupter contacts,
which spring open to disconnect the protected
wiring.
– The GFI will remain tripped until it is manually
reset, so that the cause of the trip can be corrected
safely.
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
When a ground fault occurs in the neutral
wire, neutral fault detection signal current
flows.
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
• Neutral-fault detection is an additional feature
of the GFI.
– If no load is connected, a ground fault in the
neutral conductor could escape detection.
• This situation is not nearly so dangerous as a fault in the
hot conductor, but could become dangerous if further
faults develop.
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
• To detect the condition, the GFI generates a signal,
which is induced into both conductors (i.e. it is a
common-mode signal).
– If no ground fault exists, there is no closed path for the
signal to follow, hence it causes no current and is not seen
by the detection coil.
– When a fault develops, the signal returns to its source via
the grounding system, producing a current which is
detected, causing the GFI to trip.
• The voltage and current levels at which this signal
operates are very small, and have no effect on electrical
equipment.
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

If the two currents are the same to within
about 3 mA, the GFI or GFD just sits
there.
• If the difference is greater than that value,
then a current “leak” is occurring somewhere
in the circuit, and the circuit is opened or the
alarm is triggered.

The problem with any gadget of this
type, however, is the usual story:
• They have to be checked, calibrated, and
•
repaired on a regular basis if they are to be of
any value.
They are a severe burden to the group that is
responsible for the training of new staff
members and we suggest that isolated beds
are not worth the extra cost.

It seems simpler, at least to us, to use
the best electrical beds you can afford in
regular patient areas and to stick to
mechanical cranking in the cardiac care
or intensive care areas.
• These latter locations are usually well staffed,
and the requests for changes of bed position
can usually be handled without undue
difficulty.
General Safety Suggestions for
the Use of Electrical Beds

If a patient is in an electrical bed, special
care should be exercised when liquids,
such as blood, plasma, or urine, are
present.

If you have a patient in an electrical bed and
an ECG or other electrical procedure is
required, there are two important things to
remember:
• Do not use any machine that has a grounded
patient Iead.
• In many cases, these leads are not really at zero
potential and might pass current through the patient
to the grounded bed frame.
• Do not let the patient touch any metal part of the
bed during the measurement.
• Isolate him or her with some pillows, or unplug the
bed if necessary.

If the current National Fire Protection
Association (NFPA) regulations require
that the bed be grounded, you will have
to do just that.
• You can, however, try to isolate the patient
from the bed with pillows, blankets, and the
like.
• This is a case where a regulation may have been
written with the best of intentions but the worst
results.
IN-BED ELECTRICAL
EQUIPMENT

Such appliances used in hospital beds
include
• heating pads,
• thermal blankets,
• vibratory pads,
• hair dryers,
• hot combs, and
• so forth.

There is no question about banning the
usual hair dryers and hot combs.
• Most of them are so poorly manufactured that
they constitute a hazard to a well person, to
say nothing of someone who is sick and in a
grounded electrical bed.

Heating pads and thermal blankets are a
different case:
• Many patients may really need them, and
• The hospital often provides this sort of
equipment.
• There are so-called hospital grade heating pads on
the market, and they cost more than the type you
buy at the drugstore, but they provide only a
slightly reduced risk.

The problem is that a heating pad. by its
very nature, is made of cloth, rubber, and
plastics in which electrical heating wires
are embedded.
• The insulation materials deteriorate when
exposed to the ravages of time, high
temperatures, or sharp objects, and patient
perspiration can provide all the conductivity
that may be needed to create a calamity. No
good solution exists for this problem.

The pads with plastic covers and three-wire
cords that are offered to hospitals are no help,
because there is nothing on the pad to hook
the ground wire to, in any case, a break or cut
in the cover can allow liquid into the pad.
•
If someone invents a heating pad in a grounded metal
case, it would represent an improvement, but until
then, heating pads can only be used with caution.

We suggest that a patient who has wet
dressings or is perspiring will be safer
with an old-fashioned hot-water bottle or
chemical heating pad.

Many thermal blankets use electrical heating
wires. They are therefore just big heating pads
and are susceptible to the same problems
discussed previously.
•
Some thermal blankets, however, have a network of
tubes through which heated (or cooled) water is
pumped from a bedside console.
• These units are inherently safe as long as the console
gets its power from a properly connected, three-wire
cord and the tubes in the blanket do not leak.
•
Water is a good conductor, and there is no need to make
things worse by adding salt to the solution that the
console will pump through the thermal blanket.

While we are on the subject of water and
saline solutions, it might be worth mentioning
that any solution that is being passed into a
patient will be a very good conductor if it spills
on the bed and soaks through to a bed motor.
•
Some of the stands that are used for intravenous
saline bags are pretty shaky affairs, and we suggest
that they be fixed firmly to a bed or table to preclude
their tipping over.