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6152
Storage/Use of Flammable Gases |
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1.0
Introduction
The use of flammable gases
in physics experiments presents a unique type of installation, requiring
special considerations. In many cases,
mixing of gases is involved. Large
volumes of gases may be present; thus even small leaks or ruptures of thin
windows may cause incursions into the flammable concentration region with a
large inventory to support fire. Some flammable
gases may be stored in the liquid state, increasing the inventory. Electrical equipment is an integral part of
such installations and can thus provide an ignition source if such a system is
improperly designed, fabricated, or operated.
The purpose of this procedure is to mitigate the hazards associated with
storage and use of flammable
gases.
2.0
Scope
This standard
applies to activities using flammable
gases, whether part of approved experiments taking beam or in testing labs
and shops on the Jefferson Lab site. This
standard specifically excludes liquid hydrogen target systems, gases used as
fuels, gases used for welding,
burning and brazing
procedures. See ES&H Manual Chapter 6122 Welding, Brazing, Cutting, and Grinding Safety and ES&H Manual Chapter 6150 Compressed Gases. If
the amount of flammable
gas stored at any single location exceeds 10,000 pounds, the requirements
of Occupational Safety and Health Administration (OSHA) Code of Federal
Regulations (CFR) 29
part 1910 “Occupational Safety and Health Standards,” shall also be
followed.
Flammable
Gases may be diluted with inert gas to the point where the mixture is not
flammable. This standard does not apply
to facilities using only non-flammable mixtures if they are pre-mixed and
verified when obtained. If a malfunction
of an on-site mixing apparatus could cause a mixture to become flammable, the
standard does apply to the worst case scenario.
The flammability of a mixture can be determined by referencing United
States Department of the Interior Bureau of Mines Bulletins 503 and 627. Contact the Physics Division ESH&Q Group
for copies of these bulletins or the reference section in the Jefferson Lab
library.
3.0
Classification
of Gas Storage and Usage Facilities
3.1
An analysis of the gas system shall be conducted using the
flowchart shown in Figure 1. The
analysis is based on the energy in the gas available for a fire, and classifies
gas systems in order of increasing risk.
The flowchart in Figure 1 utilizes the limits on quantities of hydrogen
gas. These quantities must be adjusted
for other gases using the heat of combustion as described in ES&H Manual
Chapter 6152 Appendix R2 Heats of Combustion.
The results of the analysis indicate the Gas System Class as described
in Table 1.
Table
1: Gas System Classes
|
Class
0 |
risk of small local flash fire |
|
Class
I |
risk of a local fire |
|
Class
II |
risk of a general fire |
Examples of gas systems analysis are given in ES&H Manual Chapter
6152 AppendixT1 Examples of Gas System
Class Determination.
3.2
The upper limit for a Class 0 gas system is the combustion energy
in 0.6 kg of hydrogen. The equivalent
quantities of some typical flammable
gases are given in Table 2. This
equivalence is scaled according to the heat of combustion of the gas.
Table
2: Maximum Quantities of Flammable
Gases Meeting Criterion for a Class 0 System
|
Gas |
Mass (kg) |
Volume (SCF) |
|
Hydrogen |
0.6 |
250 |
|
Deuterium |
1.2 |
250 |
|
Methane |
1.5 |
80 |
|
Ethane |
1.7 |
50 |
|
Propane |
1.7 |
30 |
|
Isobutane |
1.8 |
25 |
|
Dimethyl Ether |
2.7 |
30 |
3.3
Installations may be subdivided into separable parts if
restrictions exist to keep the gas flow from one part to another from exceeding
ten times the normal flow rate.
Normally, the separable parts will be in physically separate rooms. The gas system Class shall be determined for
each installation or separable part thereof using Figure 1.
3.4
Gas in cylinders connected to a piping system is included in the
quantity calculation. Nearby stored gas
may be excluded from the quantity calculations if the stored quantity is less
than the amounts listed in Table 2 for Class 0 or the storage is located
outdoors.
3.5
A written analysis of the Gas System Class is preferred; if the
Gas System Class determination has not been documented in a written analysis,
then Class II will be assigned by default.
Figure
1: Flow Chart for Risk Classification
Before
beginning to follow this flowchart, the following determination is needed:
evaluate the total gas inventory in terms of the hydrogen equivalent Q using
the heat of combustion as a scaling parameter.
The system may be separable into parts each with its own risk classification. For enclosed storage facilities, the value of
Q is determined by the total gas present.
For outdoor storage facilities, the value of Q is determined by the
largest single container or manifold system.
For systems in which the gas is not in storage, the inventory is the sum
of the mass in all containers, including detectors, piping, and manifolds.
4.0
Procedures for
Approval
4.1
Class
0
The
gas system class analysis shall be reviewed by the Physics Division
Experimental Equipment Review Committee (E2RC) or by an independent reviewer
appointed by the committee, in which case a copy of the independent review
shall be sent to the E2RC. Approval by
the Physics Division Safety Officer is required before the introduction of flammable
gas into a system.
4.2
Classes
I and II
Procedures
are the same as for Class 0, with the addition that if an independent reviewer
or review panel is appointed, the E2RC must formally concur with the report of
that review. Approval by the Division
Associate Director is required before the introduction of flammable
gas into a system.
Nothing
in this document is intended to prevent the use of methods or materials of
equivalent or superior quality to those prescribed below. The E2RC will review documented requests for
equivalency.
5.0
Requirements for
Flammable
Gas Installations
5.1
Class 0 Installations:
5.1.1
The area shall be posted “Danger-Flammable Gases, No Ignition
Sources” using standard signs available from the Jefferson Lab Safety Lab (in
Building 35 or by contacting the Physics Division ESH&Q Staff). A list of responsible persons with their
phone numbers shall also be posted.
5.1.2
Combustibles and ignition sources shall be minimized within 10
feet or three meters of gas handling equipment, piping or apparatus.
5.1.3
A pressure regulator appropriate for the gas and its environment
shall be used.
5.1.4
An orifice, excess flow valve or other fixed means of limiting the
flow to no higher than ten times the maximum operational flow rate shall be
installed.
5.1.5
All gas cylinders shall be secured. Cylinders not in use shall be capped. Empty cylinders shall be removed at the
earliest convenient date or on a predetermined, regular schedule coordinated
with vendor delivery of new cylinders. See
also ES&H
Manual Chapter 6150 Compressed Gases.
5.1.6
Enclosed volumes containing piping or equipment shall be incapable
of becoming pressurized. For example,
chest freezers shall not have latching doors.
Electrical devices enclosing or enclosed within these volumes shall be
listed for use in Class 1, Division 2 locations per NEC Article 500 or
otherwise be documented and approved as non-sparking devices.
5.1.7
Leaks from experimental devices such as drift chambers shall be
measured and documented prior to initial operation (with nonflammable gas, if
possible). Leakage above seven
liters/hour from any one chamber shall be mitigated. Recheck for leaks after major repairs or
modifications, and at least every twelve months. Leakage exceeding 20% of the lower explosive
limit at a distance over five centimeters from an identified “point” leak shall
be repaired.
5.1.8
Ventilation above one air change per hour shall be maintained in
areas using or storing flammable
gas if normal operational flow rates are less than 5 Standard Cubic Liters
Per Minute (SCLM). This ventilation may
be accomplished by mechanical or natural ventilation. For natural ventilation a room vent with a
minimum of 1/2 square foot of free area shall be provided per 1000 cubic feet
of room volume. If normal operational
flow rates are greater than or equal to 5 SCLM, supervised mechanical
ventilation in accordance with Section 7-2.2.1(a) of NFPA 58
Liquefied Petroleum Gas Code, 2004 edition shall be provided (not applicable to
outdoor Jefferson Lab storage).
5.1.9
Welding
permits (Fire Hazard Work Permit) Reference ES&H Manual 6122 Appendix T2 Fire Protection: Hot Work Permits shall not be issued
for areas within 35 feet or ten meters of the equipment containing flammable
gas unless approved in advance by the responsible Division/Section head or
designee.
5.2
Class I Installations are subject to the following additional
requirements:
5.2.1
The system, including vessels, chambers, supply and vent piping,
and exhaust points shall be labeled “flammable
gas.”
5.2.2
Piping requirements: Exceptions to this paragraph are permitted adjacent
to experimental apparatus where needed for flexibility, electrical isolation,
repairs or because of congestion. This
exception is limited to within five meters of the normal operating position.
5.2.2.1
Piping and fittings shall be protected from mechanical damage.
5.2.2.2
Piping shall be rated for the expected temperature and pressure.
5.2.2.3
Supply piping shall be metallic.
5.2.2.4
Piping shall be supported in a substantial and workmanlike manner.
5.2.2.5
Piping shall not be installed inside cable trays with electrical
conductors.
5.2.3
Joints shall be made by welding, brazing, pipe
thread, or commercial fittings appropriately installed. Custom-made fittings required by detector
design shall provide secure connections.
5.2.4
The entire piping system shall be pneumatically tested for leaks
at approximately 0.9 times the relief pressure before operating the system. Any piping with relief valve settings above
150 PSIG shall be tested at 1.25 times the relief pressure.
5.2.5
Bubblers, flow meters, and other instruments shall be securely
mounted and protected from possible breakage.
5.2.6
Provisions shall be made to purge the entire system with an inert
gas. If vacuum pumps are used for this,
they shall be listed for flammable
gas service.
5.2.7
Pressure
relief devices shall be provided to limit the pressure to the maximum
working pressure in various parts of the system. In the case of low pressure equipment,
dedicated bubblers may be used as relief devices. Common exhaust piping (where the flammable
gas vent is shared with exhaust vents for other systems) shall not be used
if equipment overpressure from any combination of devices sharing the exhaust
could result due to built up back pressure.
5.2.8
Relief devices in flammable
gas service with a capacity over two standard liters per minute shall be
vented outdoors. The exhaust locations
shall be chosen to minimize fire hazards and shall not be within 10 feet or
three meters of an air intake. Vents
shall be protected from clogging by debris, snow, or ice.
5.2.9
Flammable
gas detectors shall be installed near equipment installations, mixing
stations, and in storage sheds (the measures in this requirement are not
necessary for outdoor storage applications):
5.2.9.1
A low level alarm no higher than 10% of the lower explosive limit
(LEL) shall sound a local alarm and be used to initiate corrective
action according to a plan included in the documentation of system
operating procedures.
5.2.9.2
A high level alarm no higher than 25% of the lower explosive limit
(LEL) shall summon the Newport News Fire Department through the Jefferson Lab
fire alarm network. This high level
alarm shall also automatically shut off the supply of flammable
gas and turn off power to potential ignition sources within 10 feet or
three meters of operative gas usage apparatus.
5.2.9.3
“Crash buttons” shall be provided to accomplish the shutdowns
described above. These devices shall be
conveniently located, and one shall be adjacent to the fire alarm panel, if
present. Crash buttons should shut off
all flammable
gas sources which could conceivably be confused by unfamiliar person in a
state of panic. Crash buttons shall be
labeled “Gas System and Experiment Power Shutdown.” They shall be located on the Building
Evacuation Plan Maps.
5.2.9.4
Automatic restart of flammable
gas systems and power sources shall not be allowed after a high level alarm. This restriction is intended to require a
safety assessment of the situation. In
case of an alarm follow the local emergency plan.
5.2.10
Visual indication of the actual use of flammable
gas shall be provided at both the storage location and at the experimental
apparatus. Such lights shall be
controlled automatically and shall indicate actual “gas on” and “gas off”
status in real time. Flammable
gas alarm status shall be also be displayed at the locations of these
warning lights.
5.2.11
Possible Oxygen Deficiency
Hazards shall be addressed according to ES&H Manual Chapter 6500 Cryogenic and ODH Safety.
The hazard shall be considered for each building or room using or
storing flammable or inert gas.
5.2.12
The following documentation shall be provided to the Experimental
Equipment Review Committee (E2RC) and a copy kept
at the system site.
5.2.12.1
A general description including the types of gases to be used.
5.2.12.2
An accurate piping and instrument diagram with symbols per ISA
S5.1 (Instrument Society of America), including the normal set point of
regulators.
5.2.12.3
An instrument and valve summary.
5.2.12.4
A plan view of the installation including the locations of flammable
gas detector heads with their elevations marked.
5.2.12.5
Procedures for normal and abnormal operations including purging,
start-up, gas bottle changes, mixing, leak detection, tests, alarms, shutdown,
emergency situations, and ventilation.
5.2.12.6
Documentation and/or test results demonstrating the adequacy of
the pressure-relief system.
5.2.12.7
A call list, including home telephone numbers and available
pagers, of personnel familiar with the operation of the system.
5.2.12.8
A summary of leak-test measurements.
5.2.13
The Physics Division ESH&Q group shall be notified of actual
gas start-up and system shutdown.
5.2.14
The Physics Division ESH&Q group shall be notified before
using any types of gas not found in the stockroom, and a copy of the MSDS for
the new gas shall be provided to both the Physics Division ESH&Q group and
to the Jefferson Lab MSDS Coordinator. Reference
ES&H Manual Chapter 6610 Chemical Hygiene and ES&H
Manual Chapter 6610 Appendix T1
Material Safety Data Sheets
5.3
Class II Installations are subject to the following additional
requirements:
5.3.1
Storage and processing enclosures shall be constructed, where
practical, to comply with the guidelines of Chapter 7 Liquefied Petroleum-Gas
Liquid Transfer of NFPA-58 (see ES&H Manual Chapter
6152 Appendix T2 Standard for the
Storage and Handling of Liquefied Petroleum Gases). While this
document is specifically applicable only to LP gas storage facilities, it is a
useful guide. Exceptions may be made
with the written approval of the E2RC.
5.3.2
In addition:
5.3.2.1
All storage enclosures shall be maintained free of standing water
and/or ice to prevent falls of personnel handling gas system components.
5.3.2.2
Adequate hardware for securing all cylinders used or stored shall
be available.
5.3.2.3
Windows in gas sheds shall be wire glass set in metal frames with
a fixed sash.
5.3.2.4
Enclosures near areas of vehicle access shall be protected with
bumper posts.
5.3.2.5
The use of gas system enclosures to store oxidizers or
gases used as fuels shall be prohibited.
These enclosures shall not be used to store items not relevant to the
gas system.
5.3.2.6
Electrical installation shall comply with NEC Article 500, Hazardous
(Classified) Locations. The
classification guidelines are provided in ES&H Manual Chapter 6152 Appendix T3 Electrical Classification
Guidelines and ES&H Manual Chapter 6152 Appendix T4
Electrical Installation Guidelines.
5.3.2.7
There shall be provisions for the ventilation of such enclosures
per NFPA-58
(ES&H Manual Chapter
6152 Appendix T2 Standard for the
Storage and Handling of Liquefied Petroleum Gases). Mechanical
ventilation failure shall be alarmed.
5.3.3
The use of line-regulators downstream of cylinder regulators is
strongly encouraged.
5.3.4
Fire sprinklers shall be installed in accordance with NFPA 13
Standard for the Installation of Sprinkler Systems, 2002 edition, to protect any
adjoining or enclosing buildings from a fire in the gas storage facility. Sprinklers shall not be installed within the
gas storage facility itself since it is not desirable to quench a gas fire with
the leak still present. (Note that this
is an exception to the general rules for sprinkler installation at Jefferson
Lab.)
5.4
Outdoor Installations are subject to the following requirements in
addition to applicable Class 0, 1, or 2 requirements outlined above.
5.4.1
Outdoor installations shall meet all applicable sections of NFPA 55
Standard for the Storage, Use, and Handling of Compressed Gases and Cryogenic
Fluids in Portable and Stationary Containers, Cylinders, and Tanks, 2003
Edition and 58 for outdoor storage, use, and handling of liquefied gasses. In particular, designers of outdoor
installations are cautioned to pay attention to the requirements of these
standards for issues such as perimeter construction, roof construction, protection
of stored gas from vehicle damage, weather protection, site terrain, etc., and
to design the installation in a manner that separates adjacent storage tanks by
at least the minimum allowed value based on the size of the tanks.
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ISSUING
AUTHORITY |
CHAPTER
AUTHOR |
APPROVAL
DATE |
EFFECTIVE
DATE |
EXPIRATION
DATE |
REV. |
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ESH&Q Division |
01/26/05 |
01/26/05 |
01/26/08 |
0 |
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