1. Delivering Only Intended
Gases from the
Anaesthesia Workstation
Presented By – Dr. Dhritiman Chakrabarti
Moderated By – Dr. Poonam Kalra

2. Introduction
• Almost every piece of medical equipment carries
some risk for misuse or failure.
• Anesthetic gas delivery devices are a particular
concern because they exhibit several basic features
that may predispose to critical events and subsequent
patient injury. These include -
1. Presence of multiple connections
2. The use of complex mechanical components
3. Variations in manufacture and design.
• They are thus a target of ever continuing research to
help facilitate the delivery of anaesthesia and improve
equipment safety.

3. Gas Delivery Equipment
Gas delivery equipment will be classified by its
parts (relevant in context) and safety features in
each will be discussed accordingly.
1. Cylinders.
2. Pipelines.
3. Oxygen Failure Warning Device.
4. Oxygen Failure Safety Device.
5. Flow Adjustment Control and Flowmeters.
6. Vaporizer Manifold.
7. Gas Monitoring.

4. Cylinder Safety to Deliver only
Intended Gas
Three safety features are usually incorporated:
1. Colour Coding and Labelling of Cylinders.
2. Valve Outlet Connections for Large
Cylinders.
3. Pin Index Safety Systems.

5. Colour Coding of Cylinders
• Accidental confusion of cylinders has
been a significant cause of mortality.
Colour can be used to help identify gases.
• The top and shoulder (the part sloping
up to the neck) of each cylinder are
painted the colour assigned to the gas it
contains or the entire cylinder may be
covered by using a nonfading, durable,
water-insoluble paint.
• In the case of a cylinder containing more than one gas, the colours
must be applied in a way that will permit each colour to be seen when
viewed from the top. In some countries, the body of the cylinder is
painted with the colour of the major gas and the shoulder the colour
of the minor gas.
• An international colour code has been adopted by several countries.

6. Because of variations in colour tones, chemical changes in paint pigments, lighting effects, and
differences in colour perception by personnel, colour should be not be used as the primary means
for identification of cylinder contents. Cylinder labels are the best method to identify cylinder
contents.

7. Labelling
• Each cylinder must bear a label or decal on the side or, when space
permits, the shoulder of the cylinder (but it may not cover any
permanent markings).
1. Diamond-shaped figure denoting the hazard class
2. A white panel with the name of the contained gas
3. A signal word (DANGER, WARNING, or CAUTION, depending on
whether the release of gas would create an immediate, less than
immediate, or no immediate hazard to health or property) is present.
4. Statement of hazard
5. Should contain the name and address of the cylinder manufacturer or
distributor

8. Valve Outlet Connections for Large
Cylinders
• Larger cylinder valves have threaded outlet (bull
nose) connections.
• When the threads of this outlet mesh with those of
the nut, the nut may be tightened, causing the
nipple to seat against the valve outlet. In this way,
the gas channel of the valve is aligned with the
channel of the nipple.
• The outlets and connections are indexed by
diameter, thread size, right- and left-handed
threading, external and internal threading, and
nipple seat design.

9. Valve outlet connections for large cylinders.
A: The valve outlet thread is external, i.e., the threads are on the outside of the cylinder valve
outlet and the nut screws over the valve outlet.
B: The valve outlet thread is internal so that the nut screws into the outlet.
The specification for cylinder connections are often shown as in the following example for
Oxygen: 0.903-14-RH EXT.
The first number is the diameter in inches of the cylinder outlet.
The next number gives the number of threads per inch.
The letters following this indicate whether the threads are right hand or left hand and external
or internal. (Redrawn courtesy of the Compressed Gas Association.)

10. Pin Index Safety System
• The Pin Index Safety System
consists of holes on the
cylinder valve positioned in
an arc below the outlet port.
• Pins on the yoke or pressure
regulator are positioned to fit
into these holes.
• Unless the pins and holes are
aligned, the port will not
seat.
Pin Index Safety System The figure shows the six positions for pins on the yoke. The
pins are 4 mm in diameter and 6 mm long, except for pin 7, which is slightly thicker. The
seven hole positions are on the circumference of a circle of 9/16 inch radius centered on
the port.

12. Problems with Pin Index
Safety System
1. If multiple sealing washers
are used with a cylinder,
the pins on the yoke or
regulator may not extend
far enough to engage the
mating holes, and the Pin
Index Safety System may
be bypassed.
2. Multiple mechanical
problems can occur - Pins
can be bent, broken,
removed, or forced into the
yoke or regulator; pin index
holes may become worn.

13. User Precautions while using Cylinders:
1. Regulators, hoses, gauges, or other apparatus designed for
use with one gas should never be used with cylinders
containing other gases.
2. Adapters to change the outlet size of a cylinder valve
should not be used, as this defeats the purpose of
standardizing valve outlets.
3. No part of the cylinder or its valve should be tampered
with, painted, altered, repaired, or modified by the user.
Cylinders should be repainted only by the supplier.
4. When different types of gases are stored in the same
location, containers should be grouped by contents and
sizes (if different sizes are present).
5. Transfilling should not be performed by unskilled,
untrained person. It is best performed by a gas
manufacturer or distributor.

14. Pipeline Safety Features
• Pipelines are the backbone of institutional gas
delivery systems.
• Due to the multiple number of connections
involved, reliance on personnel for
maintenance of central supply as well as
peripheral units and the propensity to accrue
cumulative damage, pipeline systems are
prone to unintended misconnections and
crossconnections.

15. Anatomy of Pipeline System
The Branch lines end in Terminal Units which lead off to Hose Pipes which then finally
connect to the end users – Anaesthesia Workstations or ICU Ventilators.

16. Sites Prone to Cross-connections
• Cross connections are usually a result of
personnel related errors or damage issues. They
can occur at central supply and at peripheral sites
beyond the terminal units.
• Most pipeline systems are rigged to alarm based
on pressures. Delivery of unintended gas in the
pipeline within pressure range would not trigger
alarm.
• This necessitates inclusion of Oxygen analysers at
end users of the gas delivery systems i.e. the
Anaesthesia Workstation/ICU Ventilator.

17. Reported Cases of Wrong Gas Delivery
• Although an uncommon event, accidental substitution
of one gas for another at central supply can have
devastating consequences. The most common cross
overs have been between nitrous oxide and oxygen, but
various other combinations have been reported.
• Cases have been reported in which liquid oxygen tanks
were filled with nitrogen or argon. Incorrect tanks have
been placed on the central supply manifold.
• There are numerous reports of outlets labeled for one
gas that delivered another.
• The wrong outlet connector may be installed. A
terminal unit may accept an incorrect connector (due to
connector pin breakage).

18. Diameter Index Safety System
• The DISS was developed to provide
noninterchangeable connections for medical gas lines
at pressures of 200 psi or less.
• Each DISS connector consists of a body, nipple, and
nut combination.

19. • There are two concentric and specific bores in the body and
two concentric and specific shoulders on the nipple.
• The small bore mates with the small shoulder, and the large
bore mates with the large shoulder.

20. • To achieve
noninterchangeability
between different connectors,
the two diameters on each
part vary in opposite
directions so that as one
diameter increases, the
other decreases.
• Only properly mated parts
will fit together and allow the
threads to engage.
• The American Society for
Testing and Materials
(ASTM) anesthesia With increasing Compressed Gas Association
(CGA) number, the small shoulder of the nipple
workstation requires that becomes larger, and the large diameter becomes
every anesthesia machine smaller.
have a DISS fitting for each If assembly of a nonmating body and nipple is
pipeline inlet. attempted, either small shoulder will be too large
for small bore or large shoulder will be too large
for large bore.

21. Quick Connectors
• Quick connectors allow apparatus (hoses, flowmeters, etc.) to be
connected or disconnected by a single action by using one or both
hands without the use of tools or undue force. Quick connectors are
more convenient than DISS fittings but tend to leak more.
• Each quick connector consists of a pair of gas-specific male and
female components. A releasable spring mechanism locks the
components together. Hoses and other equipment are prevented
from being inserted into an incorrect outlet by using different shapes
and/or different spacing of mating portions.

22. Hose Pipes
• Hose pipes are used to connect
anesthesia machines and other
apparatus to terminal units.
• Each end has a permanently
attached, noninterchangeable
connector.
• The connector that attaches to a
terminal unit is called the inlet
(supply) connector. The connector that
attaches to equipment such as an
anesthesia machine is the outlet
(equipment) connector.
• A colour-coded hose and the name
and/or chemical symbol of the
contained gas on each connector are
desirable.

23. Test for Cross Connections
Testing for cross connections is done to
ensure that the gas delivered at each terminal
unit is that shown on the outlet label and that
the proper connectors are present at station
outlets.
1. One gas system is tested at a time.
2. Each gas is turned off at the source valve
and the pressures reduced to atmospheric.
3. The pipeline being tested is then filled with
oil-free nitrogen at its working pressure.
4. With appropriate adapters matching outlet
labels, each station outlet is checked to
ensure that test gas emerges only from the
outlets of the medical gas system being
tested.
5. The cross-connection test is then repeated
for each gas system in turn.

24. Problems
• Most problems are caused by anesthesia
providers being unaware that these systems
can fail as well as because they are not
sufficiently familiar with the system to make
emergency adjustments.
• Lack of communication between clinical
and maintenance departments and
commercial suppliers may also be a
contributing factor.
• Compliance with existing codes is not
universal.
• Intended tampering should not be overlooked.

25. Oxygen Failure Safety Device
• The anaesthesia workstation standard requires that
whenever the oxygen supply pressure is reduced
below the manufacturer-specified minimum, the
delivered oxygen concentration shall not decrease
below 19% at the common gas outlet.
• It is located in the intermediate pressure system
just upstream of the flowmeter.
• The oxygen failure safety shuts off or
proportionally decreases and ultimately interrupts
the supply of nitrous oxide if the oxygen supply
pressure decreases. On many modern machines,
the air supply is also cut off.

26. • Ohmeda machines are equipped with a fail-
safe valve known as the Pressure-Sensor
Shut-off .
• The valve is threshold in nature, and it is
either open or closed.

27. • Dräger uses a fail-safe valve known as the
Oxygen Failure Protection Device (OFPD).
• OFPD is based on a proportioning principle
rather than a threshold principle. The pressures
of all gases controlled by the OFPD decrease
proportionally with the oxygen pressure.

28. Testing the functional status of OFSD
To determine if a machine has a properly
functioning oxygen failure safety device,
1. The flows of oxygen and the other gas (usually
nitrous oxide) are turned ON.
2. The source of oxygen pressure is then removed.
3. The fall in oxygen pressure is noted on the
cylinder or pipeline pressure gauge.
4. If the oxygen failure safety device is
functioning properly, the flow indicator for the
other gas will fall to the bottom of the tube just
before the oxygen indicator falls to the bottom
of its tube.

29. Oxygen Supply Failure Alarm
• The anesthesia workstation standard specifies
that whenever the oxygen supply pressure falls
below a manufacturer-specified threshold
(usually 30 psi), at least a medium priority
alarm shall be enunciated within 5 seconds. It
shall not be possible to disable this alarm.
• The alarm is connected to the intermediate
pressure system just downstream of the
pressure regulator.

30. Because both the oxygen failure safety device and alarm depend on pressure and not flow, they
have limitations such that do not offer total protection against a hypoxic mixture being delivered,
because they do not prevent anesthetic gas from flowing if there is no flow of oxygen. Also any
operator related errors or leaks downstream still have potential for delivering a hypoxic mixture.

31. Flow Adjustment Control
• The flow adjustment controls
regulate the flow of oxygen,
nitrous oxide, and other gases to
the flow indicators.
• There are two types of flow
adjustment controls: mechanical
and electronic.
• The flow adjustment control
knobs are differentiated both by
sight as well as by touch and feel.
• The Oxygen control knob is
usually White coloured, Larger
in size and is Fluted.

32. Electronic Flow Control Devices
Some electronic flow control devices differ from
conventional pneumatic flowmeters in that the
operator only has two parameters to work with:
1. The total Flow of gas
2. Concentration of Oxygen to be delivered.
• The machine makes up the rest of the gas from
either nitrous oxide or air as is preselected.
• There is usually a mixing area that collects the
gas mixture.
• Flow and pressure transducers as well as
temperature sensors are used to maintain
accuracy.

33. Gas Selector Switch
Some machines have a gas selector switch that prevents air and
nitrous oxide from being used together.
Mechanical Gas Selector switch Electronic gas selector switch. Either nitrous oxide or
air can be selected by pushing the appropriate button
(lower left). Total gas flow and oxygen percentage are set
by pushing the hard keys and rotating the wheel at the
lower right. The balance of the fresh gas flow will be the
other gas chosen (nitrous oxide or air).

34. Flowmeter Assembly
• The flowmeter assembly located
downstream from the flow
adjustment control helps the
anaesthesiologist visualize the
gas flow and thus control it
accurately.
• It consists of the tube through
which the gas flows, the
indicator, a stop at the top of the
tube, and the scale that indicates
the flow.
• Each assembly is clearly and
permanently marked with the
appropriate colour and name or
chemical symbol of the gas
measured.

35. Flowmeter Tube Arrangement
• Flowmeter tube sequence can be a cause of
hypoxia. The figures shows four different
arrangements for oxygen, nitrous oxide, and
air flowmeters. Normal gas flow is from
bottom to top in each tube and then from
left to right at the top.
• In A/B, a leak is shown in the unused air
flowmeter, showing potentially dangerous
arrangements because the nitrous oxide
flowmeter is located in the downstream
position. A substantial portion of oxygen
flow passes through the leak while all the
nitrous oxide is directed to the common
gas outlet.
• Safer configurations are shown in C/D. By
placing the oxygen flowmeter nearest the
manifold outlet, a leak upstream from the
oxygen results in loss of nitrous oxide rather
than oxygen.

36. • Before discovering that flowmeter sequence was
important in preventing hypoxia, there was no
consensus on where the oxygen flowmeter should be in
relation to the flowmeters for other gases.
• To avoid confusion, the ASTM workstation standard
requires that the oxygen flowmeter be placed on the
right side of a group of flowmeter as viewed from the
front.
• It should be noted that having the oxygen flowmeter on
the right is specific to North America. In many
countries, the oxygen flowmeter is on the left with the
outlet also on the left.
• This sets the stage for potential operator error if a user
administers anesthesia in a country other than where he
or she was trained.
• There is no consensus on the location of the air or
nitrous oxide flowmeters as long as they do not occupy
the location next to the manifold outlet.

37. Hypoxia Prevention Safety Devices
1. Mandatory Minimum Oxygen Flow
• Some anesthesia machines require a minimum (50 to 250
mL/minute) flow of oxygen before other gases will flow. This
is preset by the manufacturer .
• The minimum flow is activated when the master switch is
turned ON.
• It may be provided by a stop on the oxygen flow control valve
or a resistor that permits a small flow to bypass a totally closed
oxygen flow control valve.
• Some machines activate an alarm if the oxygen flow goes
below a certain minimum, even if no other gases are being
used.
• The minimum oxygen flow does not in itself prevent a hypoxic
gas concentration from being delivered. A hypoxic gas mixture
can be delivered with only modest anesthetic gas flows.

38. 2. Minimum Oxygen Ratio
The anesthesia workstation standard requires that
an anesthesia machine be provided with a device to
protect against an operator-selected delivery of
a hypoxic mixture of oxygen and nitrous oxide
having an oxygen concentration below 21%
oxygen (V/V) in the fresh gas or the inspiratory
gas.
• These are of two types:
1. Mechanical Linkage.
2. Electronic Linkage.

39. Mechanical Linkage
• A mechanical linkage between the nitrous
oxide and oxygen flow control valves is
shown in the Figure.
• There is a 14-tooth sprocket on the
nitrous oxide flow control valve and a
29-tooth sprocket on the oxygen flow
control valve.
• If the flow control valves are adjusted so
that a 25% concentration of oxygen is
reached, a pin on the oxygen sprocket
engages a pin on the oxygen flow control
knob.
• This causes the oxygen and nitrous oxide
flow control valves to turn together to
maintain a minimum of 25% oxygen.
• This minimum oxygen ratio device
(proportioning system) permits
independent control of each gas as long
as the percentage of oxygen is above the
minimum.

40. Electronic Linkage
• An electronic system can be used to provide a
minimum ratio of oxygen to nitrous oxide flow. An
electronic proportioning valve controls the oxygen
concentration in the fresh gas.
• A computer continuously calculates the maximum
allowable nitrous oxide flow given the oxygen flow.
• If the nitrous oxide flow control valve is opened
sufficiently to cause a flow higher than the maximum
allowable, the proportioning valve reduces the nitrous
oxide flow to supply a minimum of 25% oxygen.
Alarms
• Alarms are available on some machines to alert the
operator that the oxygen:nitrous oxide flow ratio has
fallen below a preset value.

41. Vaporizers
• A vaporizer is a device that changes a liquid
anesthetic agent into its vapor and adds a
controlled amount of that vapor to the fresh gas
flow or the breathing system.
• Relevant to the context, the errors in intended gas
delivery can occur at two levels:
1. Wrong gas in wrong vaporizer.
2. Simultaneous administration of multiple gases.
• Failsafes to prevent such occurrences are in
place in all vaporizers.

42. Prevent Wrong Gas in Wrong Vaporizer
• Vaporizers are Colour coded and have Labels
with names of the gas they deliver.
• Same goes for the Bottles that agents are
supplied in.

43. • Filling systems are a barrier to prevent wrong filling:
1. Funnel Fill.
2. Keyed Fill.
3. Quik Fil.
4. Easy Fil.
They all have a Vaporizer end and a Bottle end which
are specific to the agent.

44. Keyed Fill:
• Each bottle of liquid anesthetic has a color-coded collar
attached securely at the neck.
• Each collar has two projections, one thicker than the
other, which are designed to mate with corresponding
indentations on the bottle adaptor.
• Bottle adaptors are also color coded.
• At one end, the adaptor has a connector with a screw
thread to match the thread on the bottle and a skirt that
extends beyond the screw threads and has slots that
match the projections on the bottle collar.
• At the other end is the male connector that fits into the
vaporizer filler receptacle. It consists of a rectangular
piece of plastic with a groove on one side and two holes
on another surface. The groove is in different locations,
depending on the agent that is to be used

46. Funnel Fill:
• A color-coded adaptor is used.
• At one end is a connector with a screw thread
to match the thread on the bottle and a skirt
that extends beyond the screw threads.
• It has slots that match the projections on the
bottle collar.
• The adaptor for a different agent than the
adaptor is intended for will not screw on
either because of different threads or bottle
opening size or because the projections will
not line up with the slots on the adaptor.
• A funnel-fill vaporizer can be converted to
an agent-specific keyed filling system by the
addition of an adaptor that screws into the
vaporizer filler

47. Quik fil is for Sevoflurane only.
• The vaporizer filler has a screw-on cap. The filler neck has three
grooves that can accept only a special filler device, which comes
attached to the bottle.
• The bottle has a permanently attached, agent-specific filling device
that has three ridges that fit into slots in the filler.
Desflurane bottle adaptor has a spring-loaded valve that opens when the
bottle is pushed into the filling port on the vaporizer.
Easy Fill:
The vaporizer filler channel are two keys
(ridges) that fit grooves on the bottle adapter.
The bottle adaptor attaches to the bottle by
aligning the notches with the projections on
the bottle collar.
The adaptor has grooves that must be aligned
with the projections on the vaporizer.

48. Some Manufacturing Fallacies
The collars on bottles of volatile inhaled anesthetics Similarly if the bottle collar for
each have large and small projections. The collars enflurane or halothane is upside
for isoflurane and sevoflurane are symmetric mirror down on the bottle, the bottle
images of each other, as are the collars for adaptor for the other agent will
halothane and enflurane. fit.

49. Hazards of Incorrect Agent Filling
• If an agent of low potency or low volatility is placed in a
vaporizer designed for an agent of higher potency or
volatility, the effect will be an output of low potency.
• Conversely, if an agent of high potency or volatility is used in
a vaporizer intended for an agent of low potency or volatility,
a dangerously high concentration may be delivered.
• If an incorrect agent is placed in a vaporizer, there will likely
be a mixture of agents in the vaporizer.
• Smelling cannot be relied on to tell which agent is in a
vaporizer, because the smell of a small amount of one agent
can completely mask the odor of a less-pungent agent, even if
the second agent is present in much higher concentration

50. Prevent Simultaneous
Administration of Multiple Gases
• Interlock (vaporizer exclusion) systems prevent more
than one vaporizer from being turned ON at a time.
• For Datex-Ohmeda vaporizers, operating the dial
release activates two extension rods that prevent
operation of any other vaporizer installed on the
manifold.

51. • A switch on the back bar may be used to direct
gas flow through only one vaporizer at a time,
e.g. the Fraser Harlake Selectatec back bar
and the Vapour changeover switch used with
Dräger 19.1 vaporizers.

52. • The Dräger Interlock 1 system for Vapour
19.2 vaporizers features a rotating bar on the
manifold with teeth that fit into a cut-out on
the back of the control dial.

54. • A mechanical locking system may be used that
only allows one vaporizer to be switched on,
e.g. Ohio selector manifolds and Dräger 19.3
vaporizers.
• The Ohio triple selector manifold allows the
left, centre or right vaporizer to be used. Slots
in the selector (arrowed) line up with flanges
on the vaporizer control dials.

55. • If none of the above is possible, mounting the vaporizer
for the most volatile agent downstream will prevent
release of high concentrations of a volatile agent owing to
contamination of a vaporizer designed for an agent with a
low saturated vapour pressure. vaporizers should be
arranged in the order:
• This will, of course, do nothing to prevent the patient
being inadvertently exposed to more than one anaesthetic
at a time.

56. Gas Monitoring
• Reliable, affordable, and
user-friendly monitors to
measure respiratory and
anesthetic gas
concentrations are now
available.
• Discussion will be
concerned with:
1. Oxygen and
N2OAnalysers.
2. Volatile Anaesthetic Agent
Analyser.

57. Classification
Based on technology:
1. Infrared Analysis (O2, N2O, Volatile agents):
• Blackbody Radiation Technology.
• Microstream Technology.
2. Paramagnetic Oxygen Analysis.
3. Electrochemical (Galvanic Cell) O2 Analysis.
4. Polarographic Electrode (O2).
5. Piezoelectric Analysis (Halogenated Agents)

58. Oxygen Analysers
• The standards for basic anaesthesia monitoring of the ASA and
AANA state that the concentration of oxygen in the patient
breathing system shall be measured by an oxygen analyzer
with a low oxygen concentration alarm in use.
• Measured by using electrochemical or paramagnetic
technology.
• Electrochemical analysis provides only mean concentrations.
Paramagnetic technology has a sufficiently rapid response time
to measure both inspired and end-tidal levels.

59. Applications of Oxygen Analyzer
1. Detecting Hypoxic or Hyperoxic Mixtures
2. Detecting Disconnections and Leaks (not reliable)
3. Detecting Hypoventilation (Steady state difference of >
5% b/w Inspired and Expired O2).
4. Measure the adequacy of preoxygenation (EtO2).
5. Expired O2 conc. – Estimated O2 Consumption –
Diagnosis Malignant Hyperthermia.
6. Concentration of nitrous oxide can be estimated from
the concentration of oxygen.
7. Detect Air Embolism (decreased diff. b/w IO2 and
EtO2)

60. Volatile Anesthetic Agents Analyzer
• The volatile anesthetic agents can be measured by using infrared
analysis, refractometry, or piezoelectric analysis.
• When an agent is used for which an analyzer is not programmed, it may
be possible to apply a conversion factor so that the analyzer may be
used to monitor that agent.
• Uses:
1. Ability to assess vaporizer accuracy.
2. Incorrect Agent detection: Agent-specific analyzers can detect an
incorrect agent, and non-agent-specific analyzers will usually exhibit
unusual readings when an agent error is made.
3. Alert the user when a vaporizer has become empty or when a
vaporizer not in use is allowing significant amounts of vapor to leak
into the fresh gas line.
• There is usually a difference between the two values, with the inspired
concentration being lower at the beginning of a case and higher at the
end. This discrepancy results from the time needed to equilibrate the
concentration in the relatively large volume of gas in the breathing
system as well as by agent uptake by the patient.

61. Caplan et al (1997), conducted a review of the Closed
Claims Project database to determine the contribution
of Gas delivery equipment (GDE) to patient morbidity
and mortality.
1. GDE accounted for 2% of all Claims.
2. 76% of the adverse events resulted in death or
permanent brain damage.
3. Misuse of equipment (75%) was three times more
common than equipment failure (24%).
4. Misconnects and disconnects of the breathing circuit
made the largest contribution to injury (35%).
5. 78% were deemed preventable with the use or better
use of monitors (Pulse Oxymeters, Capnographs).

62. Summary
As a take home message,
• adequate knowledge of the machinery that
surrounds,
• adequate perception of something that might
go wrong and,
• adequate reflexive action on part of the
anaesthesiologist if something does go wrong
are the most important preventive strategies
that are equivalent and often surpass all the
protective strategies of the machines that we
use.

63. THANKS