POWER September 2011 - 65

PLANT COMMISSIONING
Eliminate Static Electricity. In 2003, a
combustion turbine plant located in California
experienced an explosion during natural
gas blows. The cause of the explosion was
believed to be static electricity igniting an
explosive mixture of natural gas flowing at
high velocity through an ungrounded vent
pipe. The design of any natural gas venting
system must include proper grounding of the
pipe used to vent the gas blows. Don't overlook
the possibility that gas line flanges may
be electrically isolated by gaskets between
gas line and equipment flanges.
Remove Spark Sources. At the Kleen Energy
plant, several ignition sources remained
inside and outside of the power generation
building during the pipe blows. According to
the CSB, it remains " unclear whether the gas
blows were self-igniting due to expelled debris
creating a spark or through static accumulation
from the flow of the gas, ignition sources such
as electrical power, welders working, and operating
diesel-fueled heaters were in operation. "
In another incident that occurred during
a gas blow at a power station several years
ago, " the gas unexpectedly ignited, causing
a flame to shoot approximately 30 to 40 feet
into the air from the stack outlet. The gas
supply was immediately isolated and extinguished
the fire. Investigators concluded the
gas was most likely ignited by a metal particle
exiting the piping during the blow which
impacted a nearby metal surface, causing a
spark, " according to the CSB report.
Two considerations must be addressed when
considering a metal particle causing a spark.
First, to prevent a potential spark created inside
the gas line, Fluor purges and places an inert gas
in the line prior to introducing natural gas so that
insufficient oxygen is available to support ignition
inside the pipe. Second, for a spark caused
by a particle leaving the vent and impacting another
object, careful placement of the vent pipe
will ensure that any impingement/spark creation
is beyond the critical gas dispersion zone. For
added safety, a person is placed at the gas isolation
manual valve in the metering/regulation
yard to ensure that the gas is properly isolated
in the unlikely event that a spark is created and
ignition occurs.
Deenergize the Site. Eliminating ignition
sources such as welders and operating
diesel-fueled heaters is critical. However,
spark ignition potential remains with energized
switchgear.
Fluor's practice is to conduct the natural
gas blows on a weekend or at a time when
site construction and all nonessential people
are not on site. Electrical equipment in the
area of the gas blows is deenergized.
On-site staff should have portable radios to
ensure proper communication of events. All radios
should be confirmed as intrinsically safe.
64
Isolate the Site. There were seven people
at the California combustion turbine plant
when the explosion occurred, and they were
80 to 140 feet from the gas vent. The explosion
sent debris over the heads of all of those
workers. When the gas blow is under way, all
workers on site who are not involved with
the gas blow should be physically located in
a sheltered environment to prevent possible
airborne debris injuries. Commissioning staff
should be stationed in an area where they can
clearly view the vent discharge, but out of
the path of the gas exhaust. Areas around the
blow vents should be confirmed to be cleared
prior to the blows.
Gas Blow Processes
The CSB report noted that there was no planning
or safety meeting of the staff involved in the gas
blows to discuss either the gas blow procedure
or the hazards of gas blows the morning of the
Kleen Energy explosion. In fact, there were
150 workers on site that day, with nonessential
workers restricted from the immediate area of
the gas blows; however, more than 50 people
were working inside the building, although
" only 15 of the 50 were involved in the gas blow
activities, " according to the CSB report.
Fluor's commissioning processes begin
well before the day the gas blow is to occur.
The commissioning team's objectives are
aligned with engineering, construction, the
client, and the local community to ensure a
clear understanding of what a gas blow involves.
Local emergency response teams are
notified of the planned blows several weeks
prior to execution. Those teams are provided
information on the site plan layout, vent locations,
and on-site fire protection systems/
storage should it be necessary for them to assist
in an incident response.
Detailed field execution procedures are
developed to ensure proper alignment of
roles and responsibilities for a safe activity.
The team details what systems may be necessary
for use (such as fire protection distribution
and storage and gas line controls). They
also outline what systems are deenergized
prior to initiation of the blows. Finally, placement
of combustible gas monitors around the
perimeter of the gas exhaust points provides
an additional measure of safety.
Prior to the event, the required pretask
planning activities are conducted. Cleaning
of the natural gas systems presents several
unique hazards that must be considered during
the planning phase due to the explosive
nature of the cleaning media involved. The
experience gained from years of execution at
multiple sites is captured in Fluor's extensive
pretask planning tools such as its job safety
analysis, job risk analysis, safety task analysis,
and functional procedure review. Appropriate
management approval requirements
have served to ensure that safety and risk aspects
of the gas blow process are considered,
evaluated, and, if required, mitigated.
Fluor's typical gas blow strategy is to perform
the activity on the weekend to minimize
the impact to construction progress and ensure
worker safety. Site personnel are limited
to those who are essential to conducting the
gas blow. Commissioning personnel are stationed
at the metering/regulation yard to ensure
supply isolation, if needed.
Alternative Cleaning Processes
Several other alternatives for cleaning fuel gas
piping are available. On one combined cycle
project that Fluor recently commissioned,
the owner required an alternative cleaning
method. A Fluor review team investigated the
possible consequences of the alternate supply
line cleaning strategies, including the safety
aspects, possible schedule impacts, and cost
impacts (see table).
In addition to evaluating the effectiveness
of the cleaning method, the team also made
assessments of the approximate cost and
schedule for each alternative. The cost and
schedule impacts of designing and installing
exhaust points, pre-task safety discussions,
performance of the work, and post-task restoration
were considered.
Gas Line Pigging. Pigging in the maintenance
of pipelines refers to the practice of
using pipeline inspection gauges or " pigs " to
perform various operations, such as cleaning
and inspection, inside a pipeline without
stopping the flow of the product in the pipeline.
The pig is inserted into a " pig launcher, "
a funnel-shaped " Y " section in the pipeline.
The launcher is then closed and the pressure
of the product in the pipeline is used to push
A comparison of gas line cleaning alternatives. Source: Fluor Corp.
Cleaning method
Natural gas blows
Gas line pigging
Hydrolazing
Air blows
Nitrogen blows
www.powermag.com
Effectiveness
+++
+
++
++
+++
Cost
$
$
$$$
$$
$
Schedule impact
!
!!!!
!!!!
!
!
POWER | September 2011
http://www.powermag.com

POWER September 2011

Table of Contents for the Digital Edition of POWER September 2011

Contents
POWER September 2011 - Cover1
POWER September 2011 - Cover2
POWER September 2011 - Contents
POWER September 2011 - 2
POWER September 2011 - 3
POWER September 2011 - 4
POWER September 2011 - 5
POWER September 2011 - 6
POWER September 2011 - 7
POWER September 2011 - 8
POWER September 2011 - 9
POWER September 2011 - 10
POWER September 2011 - 11
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