Design Basis
SMOF Staging Removable Roof Enclosures
Project Scope (Summary):
Design and construct a "Rubb" style building to serve as a portable roof enclosure for the structural steel
staging inside of SMOF (Bldg. 4900). Roof enclosure to provide a portable blast and paint enclosure to
support special hull treatment operations from the staging. 4 interchangable roof enclosures will be
constructed (3 Low Roof types and 1 High Roof type). Each enclosure will have electrical and fire
protection systems which will connect to in place systems on the staging. The enclosures’ mechanical
system will be supplied by portable HVAC equipment and is not in scope of work.
Code Classification:
Each roof enclosure shall be classified as a portable spray booth. The enclosure will isolate the work
zone from the larger SMOF fabrication area. The purpose of the spray paint enclosure is twofold; first the
enclosure must contain any fire from spreading to adjacent fabrication areas, and secondly the enclosure
must protect the environment by collecting the volatile organic compounds (VOCs) before they are
released into the atmosphere.
The portable spray enclosure design shall conform to requirements of the following applicable
regulations:
A. Occupational Safety and Health Administration (OSHA) 29 Code of Federal Regulations (CFR)
1910
B. National Fire Protection Association (NFPA) Standard 30, “Flammable and Combustible Liquids
Code”
C. NFPA Standard 33, “Spray Application Using Flammable or Combustible Materials”
D. NFPA Standard 70, National Electrical Code (NEC)
E. International Code Council, Building Codes, 2009
Code interpretations and the code reference are listed as follows:
1. The International Building Code (IBC) defines the overall SMOF Building as Construction Class
Type F2, Low Hazard Occupancy structures (2009 IBC, Para. 306.1).
2. Spray areas shall be separated from other operations by at least 3 feet or by a 1-hour rated fire
wall (NFPA 33 Para. 5.1.6). However, the IBC Para.416.2 does not mention a 3-foot separation.
The IBC is more stringent and a 1-hour wall is required.
3. The spray booth shall be specifically designed for the purpose of blasting and painting only
(NFPA 33 Para. 3.3.14 and 15, Para 4.1).
4. The spray booth shall be protected with an automatic fire suppression system (NFPA 33 Para
9.1).
5. Walls and ceilings of the booth shall be noncombustible and shall be securely mounted or rigidly
fastened to the structure. Interior walls shall be smooth to facilitate ventilation and cleaning
(NFPA 33 Para. 5.1). The OSHA 1910.107.b adds the requirement that spray booths shall be
substantially constructed of steel or concrete/masonry.
6. Use of aluminum in spray booths is not allowed for structural support and ductwork. Aluminum is
allowed for platforms, interior components, spray apparatus components and other ancillary
devices (NFPA 33 Para 5.13).
7. Means of egress from paint spray booth/rooms must comply with NFPA Life Safety Code 101.
The occupancy of each enclosure will be approximately (6) people.
Structural Design:
NNS intends to construct (4) portable roof enclosures for the vessel access staging inside of SMOF.
Three low roof enclosures and one high roof enclosure will be constructed. The intent is for three of the
roof enclosures to cover an entire bay inside SMOF and for the fourth enclosure to be used as an
auxiliary enclosure in an additional bay. Each enclosure will be approximately 46 feet wide by 33 feet
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Design Basis
SMOF Staging Removable Roof Enclosures
long. The three low roof enclosures will have a minimum clear height of 12 feet. The high roof enclosure
will have a minimum clear height of 30 feet.
The roof enclosures will attach the 4th level (32’-6” Elevation) of structural staging in the SMOF.
Connection must be designed to allow for ease of attachment and removal. See attached structural
staging drawings for connection members.
The roof enclosures must be crane liftable to allow for relocation within the SMOF from bay to bay. The
lift points must be at the base of the structure to allow for lifting connections to be made from the 4 th level
of the structural staging.
Crane rigging design must be developed to allow for the roof enclosures to pass above the center
building platform in SMOF. SMOF crane hook height is 100’-0” above finished floor. The top of the ship
supply/exhaust ventilation on the building platform is approximately 50’-6” above finished floor. Therefore
there is a clearance window of 49”-6” for the roof enclosure and all of its rigging.
The ends of each enclosure shall be designed as retractable enclosures from the roof height down to the
base. This is required to allow for each enclosure to be used in an end or center condition. The
enclosure shall provide a sealable connection between each enclosure. The high roof enclosure may
have a permanent end wall from its roof height down to the low roof height. The high roof end wall shall
be retractable from the low roof height down to its base.
Each enclosure shall be designed with a retractable level of staging on the side walls only and installed
approximately 5’ above its base. Staging shall extend approximately 13’ from the side walls.
The structural design shall meet the following code requirements:
1.
2.
3.
4.
5.
Dead Load requirements of Structure
Live Load of 25 psf with a safety factor of 2.0 prior to code load factors
Interior Structure with Basic Wind Speed of 35 mph (Importance Factor = 1.0)
Seismic Use Group II (Importance Factor = 1.0, Site Class = E)
Snow Load Not Applicable – Interior Structure
Mechanical Design (Not in Project Scope):
Mechanical design is not included in the scope of work. Conditioned air will be provided for the portable
enclosures with several portable AC units. Conditioned air is ducted into the enclosure from the HVAC
units taking air from the surrounding plant area. The air is then exhausted through temporary ducts to
either a dust collector located outdoors during the blasting operation or to temporary fans ducted outside
during the painting operation.
The portable units will meet the following code requirements:
1. Exhaust ventilation is required in accordance with NFPA 91. The flow of air through the booth
shall be 100 fpm (OSHA 1910.107.b.5.1) or the total air volume exhausted shall dilute vapors to
at least 25 percent of the lower explosive limit (LEL) of the paint/solvent being sprayed (NFPA 91
Para. 4.1.3 and NFPA 33 Para. 7.2).
2. Exhaust plenums, ducts and fasteners shall be constructed of steel unless the painting operation
is powder coated, which can be fire retardant combustible materials (NFPA 33 Para. 7.7 and
OSHA 1910.107.d.7).
3. Makeup air is required equal to the exhaust. Minimum temperature of makeup is 65°F (NFPA 33
Para. 7.3).
4. Exhaust shall be routed directly outside of the building. The exhaust shall not penetrate any
building fire wall. The termination shall be 6 feet away from exterior wall, 25 feet for any
combustible construction and 25 feet from any unprotected openings (NFPA 33 Para. 7.4 and
OSHA 1910.107.d.8). Based on the SMOF design, the exhaust system terminations are 50 feet
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Design Basis
SMOF Staging Removable Roof Enclosures
away from any intakes and located up high above grade. Based on the code interpretations this
complies with the codes referenced.
5. Sufficient space (minimum 3 feet) shall be provided to permit airflow and maintenance on all
sides of the enclosure (NFPA 33 Para. 5.3.2).
Fire Protection Design:
Each roof enclosure will contain its own fire protection system. The roof enclosure fire protection design
must be coordinated with structural staging fire protection design. The portable enclosure will have quick
connect couplings which will attach to the staging fire protection system. Quantity and location of
connections to staging fire protection must be coordinated.
The fire protection design shall meet the following code requirements:
1. A fire suppression system is required. A wet sprinkler is the first allowed, but other systems such
as chemical, automatic foam, carbon dioxide, dry chemical and/or a gaseous agent fire
suppression system are permitted. At a minimum, the fire suppression system should be wetsprinkler type (NFPA 33 Para 9.1.1).
2. The sprinkler system shall be designed per Extra Hazard (Group 2) per NFPA 13 (NFPA 33 Para.
9.4.2), unless powder-coated which can then comply with Ordinary Hazard (Group 2) (Exception
No. 2 to Para 9.4.2).
3. The fire sprinkler system shall be controlled by a separate listed indicating valve operable from
floor level (NFPA 33 Para. 9.4.5).
4. Sprinklers protecting spraying areas shall be protected from the accumulation of residue from
spraying operations. Sprinklers are permitted to be covered by cellophane bags having a
thickness of 0.08 mm or less or by thin paper bags and shall be replaced frequently so heavy
deposits do not accumulate (NFPA 33 para.9.4.71).
5. Portable fire extinguishers shall be provided in each spray paint operation area or compartment in
accordance with NFPA 10. The fire extinguishers shall be suitable to handle the most flammable
of the coating materials being used (NFPA 33 Para 9.6 and OSHA 1910.107.g).
6. Portable fire extinguishers for Extra Hazard Class B (class for paints and lacquers per NFPA Para
5.2.2) fire shall have a rating of 40-B and be no more than 30 feet maximum travel distance
(NFPA 10 Para. 6.3.1.1).
7. If filters are used or required in the exhaust duct for a spraying operation, sprinklers shall be
required both upstream and downstream of the filters (OSHA 1910.107.b.5.iv).
Fire alarm and fire protection system shall meet the requirements of NFPA 72 as required by NFPA
33 Para 9.1.3.
Electrical Design:
Each roof enclosure will have its own electrical system. The enclosure must be lit to 55 foot candles for
blasting and painting operations. Electrical power supply shall be coordinated with the SMOF building
electrical design and SMOF staging electrical design. Each enclosure shall have a temporary power
connection exterior of the enclosure. NNS shall provide temporary cable for connection. Receptacles for
blasting and painting equipment shall be provided inside or outside of enclosure.
The electrical design shall meet the following code requirements:
1. The electrical wiring and equipment shall be rated for Class 1, Division 1 (NFPA 33 Para 6.4.1).
2. Electrical wiring/equipment shall be explosion-proof type approved for Class I, Group D locations
(OSHA 1910.107) and Class I, Division 1 (NFPA 70 Para 516.4).
3. Lights, installed within the enclosure, shall be explosion proof and UL listed approved for Class 1,
Group D atmospheres (OSHA 1915.35.b.7) and Class I, Division 1 (NFPA 70 Para 516.4). An
alternate to having lighting fixtures within the enclosure is placing the lighting fixtures outside of
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Design Basis
SMOF Staging Removable Roof Enclosures
4.
5.
6.
7.
the booth, behind a glass panel, allowing for access and maintenance outside of the booth (NFPA
33 Para 6.6 and NFPA 70 Para 516.4(C)).
Portable lamps shall not be used in any spray booth during spraying operations (NFPA 33 Para.
6.9). Exception: If portable lamps are used during cleaning or repair operations, the lamps must
be approved for Class I locations as defined in NFPA 33, NFPA 70, (NEC Para 516.4(D)).
All electric motors within spray area shall be explosion proof (OSHA 1915.35.b.5).
All metal parts of spray booths, exhaust ducts, and piping systems that convey flammable liquids,
combustible liquids, or aerated solids shall be properly grounded (NFPA 33 Para 6.8 (3) and
NFPA 70 Para 516.10(A)(6)).
There shall be no electrical equipment in any spraying area where deposits of combustible
residues may readily accumulate. An exception exists for wiring in rigid conduit, boxes, or fittings
that do not contain taps, splices, or terminal connections (NFPA 70 Para. 516.4(B)).
Attachments:
1. Building 4900 SMOF Vessel Access Staging Drawings 386644-386869
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