January 3, 2001

TECHNICAL BULLETIN – 010

Electrical Safety in the Marine Environment
Approach Boundaries

Electrical Safety in the Marine Environment

presented by

Cadick Corporation

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Overview

Electrical power systems on shipboard have increased in voltage level as well as complexity. These
changes require a fresh look at the issue of electrical safety. Distribution systems on vessels are now
weighing in at 6600 Volts instead of 450 Volts. This means that virtually all procedures must be
reworked to accommodate the increased hazard levels presented by such voltages. While intended
primarily for application to medium voltage (above 1000 Volts and less than 100,000 Volts, the general
concepts covered in this bulletin can and should be applied to the entire electrical system. This bulletin is
divided into five (5) basic sections as follows:

1. Overview
2. Risk Assessment
3. Safety Related Design Recommendations
4. Safety Related Work Practices Recommendations
5. Ship=s Force Safety Related Training Recommendations

Sections 3 through 5 contain recommendations developed based on three criteria:

1. The risk assessment discussed in Section 2

2. The collective experience of the key members of the Cadick Corporation research team in both
land-based and marine facilities.
3. The experience gained by Cadick Corporation during startup and training of personnel on-board
the Coast Guard Ice-breaker Healy (WAGB - 20).

While electrical safety and hazard analysis are, to some extent, subjective in nature, analytic methods
that are provided that are unique in the industry and in previous efforts.

Note that the recommendations given in this report are intended primarily for application in the medium
voltage sections of a marine power system; however, the general principles will apply equally to 450
Volt gear. The principle differences between the older, low voltage systems and the more modern
medium voltage systems lies in the energy level and the degree of current flow during contact (shock) or
arcing events. Because of the greater amount of energy in the medium voltage system, more stringent
requirements must be put in place for personnel insulation and flash protection.

Risk Assessment

Medium voltage electric distribution systems are not new. Since safety equipment and procedures for
such systems have long been established, the primary purpose of this analysis is to estimate the
increased electrical safety risks involved when medium voltage electric distribution is applied on board
a ship.

There are many activities that bring personnel into close proximity with medium voltage distribution
systems, and for which electric safety is paramount. These activities are summarized below:

! Switching. The act of energizing or de-energizing electrical facilities. This may be done
routinely and during emergencies, as when:
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 C de-energizing loads and portions of the system
C restoring service to facilities
C transferring load from one source to another
C clearing electrical faults
C isolating electrical faults

! Activities in the presence of electrical conductors that are known to be energized.

C recording measurements and relay targets

C measurement of electrical quantities
C live maintenance and/or troubleshooting

! Activities in the presence of conductors that are known to be de-energized. It is assumed that the
de-energized status of equipment and conductors has been verified in accordance with
appropriate safety procedures including lockout/tagout, and equipment is grounded and short
circuited to create an equipotential zone.

C equipment maintenance and overhaul

C equipment cleaning
C protective device testing and calibration
C breaker trip testing
C insulating testing

! Activities in the presence of conductors that may be energized. The status of conductors has not
been verified to be de-energized.

C safety voltage measurement

C replacement of fuses
C racking in or out of breakers

Although routine maintenance is normally expected to be performed while the ship is in port, emergency
maintenance and troubleshooting can be required at any time. Therefore we expect and assume that such
activities will occur at roughly the same frequency as in land based medium voltage electric power
systems.

Furthermore, the risk of equipment misoperation and failure are expected and assumed in this analysis to
be essentially the same as land based systems. There is nothing a marine power system that would
indicate a drastic difference in expected component performance. Of course, this assumes normal
operations. Activities during combat or emergency operation are unpredictable and subject to temporary
repeal of normal procedures.

While there is more use of power semiconductors in marine systems than in conventional medium
voltage distribution systems, this technology is confined to power conversion modules which create
multiple DC and variable frequency AC voltages. For the sake of a conservative approach, the
application of such technology is assumed to have no impact on the overall safety of personnel. Since
fast acting semiconductor power supplies can greatly reduce the electric arc hazard, revisions may be
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required as system designs mature.
Those differences between land based electric distribution and shipboard medium voltage distribution
having the greatest impact on electrical safety are as follows (in the order of impact):

! The clearances are smaller. The space available for personnel activities is greatly reduced.

! Personnel are more likely to be inexperienced with medium voltage equipment, only because
medium voltage distribution has not until recently been generally applied aboard ship.

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 Impact of Shipboard
Impact of Shipboard Application
Hazard Description Application on the
on the Likelihood of Hazard
Consequence of Hazard
Maintaining proper clearance from
energized conductors may be much more
difficult in a confined work space. Contact
with these conductors is therefore more
The hazard is severe likely. Inexperience with the tools and
injury up to and procedures of medium voltage electrical
including systems may increase further the There is nothing in marine
electrocution, when likelihood of mishap. This may be offset applications or the description
electrical current somewhat by the fact that equipotential of the IPS indicating any
Shock zones are much easier to set up on
comes in contact with change in the severity of the
the human body and shipboard. consequences of contact with
even is conducted There is nothing in the marine application electricity.
through it. or IPS design that makes shock inherently
morelikely. The likelihood of a shock
hazard occurring is, in reality, the
likelihood of an accident. Table 2
discusses the likelihood of accident more
thoroughly.
Electrical arcs of
sufficient energy can The amount of damage
cause fatal burns at experienced diminishes as the
distances of up to 8 square of the distance from the
feet or more. Even if Because of the relatively more compact arc. Twice as far means one
Arc the direct burns are construction of the IPS, electrical arcs may fourth the damage. Personnel
not immediately be marginally more likely to occur. forced into closer proximity
fatal, clothing can be with the arc will experience
ignited and lead to geometrically increased
fatal secondary thermal damage.
burns.
An electric arc
Confined work areas force
superheats the air
personnel into closer proximity
instantaneously. The
with the force of the blast.
expansion of the air
Personnel are at the same time
can reach pressures
more likely to be exposed, and
of 200 pounds per Since arcs may be marginally more likely,
Blast will suffer greater from the
square foot, sufficient blast will also be more likely.
exposure. Additionally, the
to explode
confined area can have the
switchgear, push over
effect of enclosing and
concrete walls, and
concentrating the effect of the
turn sheet metal into
blast.
shrapnel.
Table 1
! There is more metal surrounding work spaces. This makes it easier to establish equipotential
surfaces and thus reduce step and touch potentials.

Risk is often determined as the product of the likelihood of an incident and the magnitude of the
consequences once the incident occurs. We determine separately the impact of the above differences on
the likelihood of a Asafety incident@ and the consequence of that incident. Table 1 summarizes our
qualitative thinking with regard to electrical hazard.
Next we look at the categories of activities, and the impact of marine application on their safe
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accomplishment. Table 2 summarizes:
A quantitative assessment involves, at least initially, a judgement of relative magnitudes. The following
magnitudes were assumed in this analysis. While they are based on our judgement and experience, the
effect on the overall analysis of assuming different initial values will be readily apparent.

Table 1 & 2 together show that the impact on the likelihood of an electrical safety incident is dominated
by the impact on the likelihood of an accident, while the impact on the consequences of an incident is
Impact of Shipboard Application on the Impact of Shipboard Application
Activity
Likelihood of Accident on the Consequence of Accident
The equipment itself is not more (or less) likely to
fail or misoperate. There is some increased
Switching likelihood of misoperation due to the inexperience
of operators and/or to the closer quarters in which
they must work.
Maintaining proper clearance from energized
Activities in the conductors may be much more difficult in a
presence of electrical confined work space. Contact with these
conductors that are conductors is therefore more likely. Inexperience
known to be with the tools and procedures of medium voltage
energized electrical systems may increase further the
The consequences of an electrical safety
likelihood of mishap.
accident are the same as with land
Inappropriately applied or failing grounds are not based systems, namely: exposure to the
Activities in the
more (or less) likely aboard ship. Accidental re- hazards of shock, arc, and blast. The
presence of
energization is likewise not more (or less) likely in impact of marine applications on these
conductors that are
marine applications. Exposure to voltage is slightly hazards is described in Table 1.
known to be de-
reduced by the improved quality of established
energized.
equipotential surfaces.
It is not more (or less) likely that energized
conductors are undetected in marine applications.
However, maintaining proper clearance from these
Activities in the
conductors may be much more difficult in a
presence of
confined work space. Contact with these
conductors that may
conductors is therefore more likely. Inexperience
be energized.
with the tools and procedures of medium voltage
electrical systems may further increase the
likelihood of mishap.
Table 2
dominated by the impact of the electrical hazards. This simplifies the next stage of analysis: the
quantitative assessment.
Keep in mind that our goal is not to evaluate the absolute risks of various activities, or even compare
them. We are assessing the increase in those risks as a result of the marine application.

Table 3 shows the assignment of magnitudes.

Looking at the top part of Table 3:

! The impact on the likelihood of a safety incident for activities in the presence of energized
conductors, and conductors that may be energized, is the same, and given the highest value.

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 Likelihood Shock Arc Blast
! The impact on the likelihood of an
incident when switching is somewhat less, Switching 1.2 1.2 1.2
though there is still an increased Energized 1.5 1.5 1.5
likelihood over land based systems. This
not because the equipment is more likely De-energized 0.8 0.8 0.8
to fail or misoperate in a marine May be Energized 1.5 1.5 1.5
application; rather, it is because the
Consequence Shock Arc Blast
operators likely to be less experienced.
Switching 1.0 2.0 3.0
! The impact on the likelihood of a Energized 1.0 2.0 3.0
electrical safety incident when conductors
are de-energized is to make these De-energized 1.0 2.0 3.0
activities somewhat safer on board a ship, May be Energized 1.0 2.0 3.0
due to the improved quality of the
equipotential surfaces. Recall that it is assumed for these activities that the de-energized status
of equipment and conductors has been verified in accordance with appropriate safety procedures,
and safety grounds and short circuits have been applied to create an equipotential zone.

Looking now at the bottom half of Table 3:

! The consequences of electrical shock are unaffected by marine application.

! The full integer multiplier for the impact of marine application on arc damage is justified by the
geometric relationship between proximity and resultant damage. A reduction of 29% in the
distance between the arc and the operator will double the thermal damage.

! Blast has a higher multiplier due to the added effect of confined areas to concentrate the blast and
magnify its impact.

As stated earlier, the total impact on risk is established by multiplying the impact on likelihood by the
impact on consequence. See Table 4.

While not materially affecting the final results, the composite risk value is obtained by taking a
numerical average of the shock, arc, and blast hazards. From this we conclude that, nominally, medium
voltage electric power distribution systems are between 1.6 and 3 times more hazardous to operating
personnel when applied aboard a ship. Not all activities are impacted equally, and Table 4 Table 5 show
the increased risk for each activity.

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 Risk Relative to
Activity Land Based Safety Notes
Systems
Personnel must be qualified and familiar with the
equipment. Risk can be mitigated with focused training.
Switching
C de-energizing loads and
Only one person should be in the switchgear compartment to
portions of the system 240% more risk, due to
perform switching. Another person should be outside, with
C restoring service to reduced clearances and
a remote communications device. Second person is more
facilities confined work spaces,
likely to survive a blast and initiate appropriate rescue.
C transferring load from and inexperience of
one source to another personnel.
Personnel need to strictly adhere to proper safety
C clearing electrical faults
procedures, especially with respect to body and face
C isolating electrical faults
protection, and positioning that limits as much as possible
exposure to heat, molten metal, and flying debris.
Activities in the presence of
electrical conductors that are Live maintenance is the riskiest behavior in this category,
known to be energized 300% more risk, due to and should be avoided unless absolutely necessary.
C recording measurements reduced clearances and
and relay targets confined work spaces, Comments above apply as well.
C measurement of and inexperience of
electrical quantities personnel. Test equipment must be operated in strict adherence to safe
C live maintenance and/or procedures.
troubleshooting
It is assumed that the de-energized status of equipment and
Activities in the presence of conductors has been verified in accordance with appropriate
conductors that are known to be safety procedures, and safety grounds have been applied as
160% more risk, due to
de-energized. appropriate.
reduced clearances and
C equipment maintenance
confined work spaces,
and overhaul Grounding procedures must be adhered to strictly, to
and inexperience of
C equipment cleaning establish an equipotential zone.
personnel, mitigated
C protective device testing
somewhat by better
and calibration Facility must provide appropriate lugs for attachment of
equipotential surfaces.
C breaker trip testing ground clamps.
C insulating testing

Activities in the presence of

conductors that may be energized. Racking in and out of breakers is the riskiest behavior in this
The status of conductors has not category, as the visible open is not designed to interrupt load
been verified to be de-energized 300% more risk, due to or fault current.
C safety voltage reduced clearances and
measurement confined work spaces, Comments under switching apply.
C installation and removal and inexperience of
of grounds personnel.
C replacement of fuses Test equipment must be operated strictly according to safe
C racking in or out of procedures.
breakers
Table 4

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Safety Related Design Recommendations

Based on the three criteria identified in the Overview section of this report, the following design criteria
should be considered in a medium voltage marine power system.

1. Arc-resistant switchgear

Arc resistant switchgear is electrical gear that is, by design and construction, less likely to incur electric
arcs and more capable of reducing the consequences
of electrical arcs. It does so as identified in Figure 1. 1) Minimize Likelihood of arc occurring
At the present time at least three (3) major a) Insulated bus
manufacturers are constructing arc-resistant b) Adequate bus spacing
switchgear. 2) Reduce Consequences of Arcs
a) Enhanced construction materials and
All portions of a marine power system should be methods
manufactured using arc-resistant switchgear b) Pressure relief vents
techniques. c) Chambers to re-direct pressure
d) Multiple Pressure Chambers

Figure 1 - Arc Resistant Switchgear

2. Permanently mounted safety grounding connectors

Electrical safety grounding is

one of the premiere methods
used to prevent injury in the
event that a de-energized system
should become unexpectedly re-
energized. The basic purpose of
safety grounding is to create a
zone of equalized potential
(equipotential zone) surrounding
workers so that, in the event the
system becomes inadvertently
energized, workers are fully
protected and surrounded by
metal conductors. Figure 2
illustrates the basic concept of
safety grounding as it applies to
metal clad gear similar to that
being used in the modern
marine systems.
Figure 2 - Grounding Metal Clad Gear
One of the great difficulties in applying safety grounds is the wide number of clamp styles required by
the various shapes and sizes of electrical bus work. This problem can be resolved by the use of
permanently mounted clamp connection points. These devices, as illustrated in Figure 3, are stock items
available from a number of safety equipment manufacturers.
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Note that the connection device is similar in appearance to the commonly used Abumper hitch. @ The
device is permanently bolted to the electrical bus in appropriate locations, thus providing a secure
connection point for the electrical safety grounds. Naturally the connection devices must be selected
based on the specific system parameters such as available fault current, space available, and so on.

3. Use of current, voltage, and control test switches

During commissioning tests on the US Coast Guard Cutter Healy, we observed that testing and
calibrating instruments was made extremely difficult because no connection points were available.

Several manufacturers make test connection plugs and/or switches for protective relays and other types
of system instruments. These devices are usually
mounted on the same panel which holds the
instrument. To apply voltage or current for testing
purposes, the technician need only insert the
appropriate test lead.

Note that using this type of equipment eliminates

the hazard normally associated with opening
current transformer circuits since the test device is
provided with a mechanism which automatically
bypasses the current transformer circuit.

4. Clear and consistent labeling of all system

components

Because of the bidding system employed by the

Federal Government, different parts of the power
system may be provided by different
manufacturers. Prior to issuing specifications Figure 3 - Ball and Socket Grounding Connection
to manufacturers, designers should insure that
all equipment marking and labeling standards are clearly indicated. During commissioning of the Healy,
we observed that different modules used different labeling techniques. This made identification of the
equipment and the test results very difficult. It will be equally difficult for ship=s force during operations.

5. All additional requirements as described in CFR Title 29 Parts 1910.302-308, and National Fire
Protection Association NFPA 70E

CFR Title 29 Parts 1910.302-308 (OSHA Electrical Safety Design Standards) and the National Fire
Protection Association NFPA 70E are among the electrical design documents used for land-based
systems. Since these standards have proven track records, they should also be used by designers of the
IPS system.

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6. Other Agood practice@ design procedures which, while not necessarily required by regulatory
standards, will provide the ultimate level of personnel safety. Such design items might include:

a. Mimic bus designs on the front of all switchgear

b. Color coding of cables to distinguish medium voltage (orange for example)

Safety Related Work Practice Recommendations

1) Required safety equipment for personnel (PPE)

a) Rubber insulating equipment (rated for both low and medium voltage applications)
i) Gloves with appropriate leather protectors
ii) Blankets
iii) Sleeves
b) Insulating hard-hats
c) Eye protection with UV protection
d) Thermal protective clothing (Nomex, PBI, or Kermel recommended.)
e) Insulated hand tools
f) Safety rated voltage measuring instruments

The equipment in the above list should be available in sufficient quantities that at least
two persons will be fully equipped for working on or near energized or potentially
energized equipment for all possible combinations of normal and emergency operations.
At a minimum we recommend at least ten (10 complete sets.)

2) Strict observance of clearance distances

OSHA standards, and more recently NFPA 70E, have clearly established the concept of approach
distances. An approach distance is defined as how close a worker may approach an exposed energized
conductor (or one whose
energization state is Energized
unknown), without using Item Limited
extra safety equipment and Prohibited
safety related work
practices. Figure 4
illustrates these clearance
distances as defined in
NFPA 70E. The clearance
distances can be defined Restricted
based on NFPA 70E Table
2-1.3.4 and/or suitable Flash
Protection
formulas during the

Figure 4 - NFPA 70E Approach Boundaries

specific safety design procedures for the electrical system. Key to these observances will be the use of
appropriate procedures to determine what specific safety equipment is required to be allowed to break
the various safety boundaries.
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3) Establish clear-cut lockout/tagout requirements

Equipment should not be considered de-energized until it has been voltage measured, locked, tagged,
and safety grounded. The lockout/tagout procedure is the principal element in this package. Basically the
steps are as follows:

a. De-energize the equipment using the appropriate breakers and/or control switches
b. Apply safety locks and tags to the equipment in such a way that the gear cannot be re-energized
without removal of the lock.
c. Try to re-energize the equipment to verify that the locking procedure was successful.
d. If exposure to electrical conductors will occur, make a three step voltage measurement to verify
that the system is de-energized and no electrical energy is present.
e. After the voltage measure is performed, apply electrical safety grounds as appropriate to the task
at hand.

4) Establish a systematic procedure to determine if and when energized work is required. Generally
speaking the flow chart decision tree shown in Figure 5 or some similar method should be
employed to determine the need to work on equipment with it energized. The additional hazards
discussed in Figure 5 include items such as shutdown of ventilation equipment, shutdown of life
support equipment, and removal of illumination. Examples of work requiring energization
include activities such as troubleshooting or voltage measurements.

5) Use of team concepts

When working on circuits in excess of 1000 Volts which are, or may become, energized, we strongly
recommend the application of the team concept. That is, work teams should be set up in teams of two, at
a minimum. A summary of such activity is briefly described in Table 5 on the next page.

Ship==s Force Safety Related Training Recommendations

All ship=s force who are exposed to electrical hazards in excess of fifty Volts (50 V) to ground should be
provided in depth, hands-on training experience in the following topics:

1) Nature and characteristics of the electrical hazards

2) Voltage Measurement techniques
3) Lockout/Tagout
4) Clearance distances
5) Application of Safety Grounds
6) Safe use of tools and equipment
7) Electrical hazard recognition and avoidance
8) Confined space electrical hazard avoidance

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Figure 5 - Hot Work Decision Making Flow Chart

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