Testimony of Dr. S. Shyam Sunder 

Acting Director, Building and Fire Research Laboratory 

National Institute of Standards and Technology 

Technology Administration 

U.S. Department of Commerce 

Before 

New York City Council 

Joint Meeting, Committees on Lower Manhattan 

Redevelopment; Fire & Criminal Justice Services 

Hearing on 

“Oversight - Issues of Health and Safety Regarding the 

Storage of Diesel Fuel at 60 Hudson Street, Manhattan” 

September 8, 2006 

 
Chairman Gerson, Chairman Martinez, members of the Committees, I am pleased to 

appear today to testify on the National Institute of Standards and Technology’s (NIST) 

preliminary findings with regard to the collapse of World Trade Center 7 and the diesel 

fuel that was stored in that building. 

The objectives of NIST’s federal building and fire safety investigation of the World 

Trade Center disaster with respect to WTC 7 are to: (1) determine why and how the 47-

story building collapsed; (2) determine the procedures and practices that were used in the 

design, construction, operation, and maintenance of the building; and (3) identify, as 

specifically as possible, areas in current national building and fire model codes, 

standards, and practices that warrant revision. 

NIST issued a progress report in June 2004 that contained information regarding our 

work on WTC 7 (page 17 of Volume 1 and Appendix L). NIST also issued reports 

documenting the fuel system present in WTC 7 (NCSTAR 1-1, Chapter 12 and NCSTAR 

1-1J) in October 2005. These reports are available on the dedicated NIST World Trade 

Center website, http://wtc.nist.gov. 

After the June 2004 progress report on was issued, NIST stopped working on WTC 7 and 

staff were assigned full-time through the fall of 2005 to complete the investigation of the 

WTC towers. 

With the release and dissemination of the report on the WTC towers in October 2005, the 

investigation of the WTC 7 collapse resumed. Considerable progress has been made since 

that time and it is anticipated that a draft report will be released by early 2007. 

In the June 2004 Progress Report, NIST presented a working hypothesis for the collapse 

of the 47-story WTC 7. If it remains viable upon further analysis, this hypothesis 

suggests that WTC 7 was a classic progressive collapse that included: 

• An initial local failure at the lower floors (below floor 13) of the building due to fire 

and/or debris induced structural damage of a critical column (the initiating event), 

which supported a large span floor bay with an area of about 2000 ft2

; 

• Vertical progression of the initial local failure up to the east penthouse, as large floor 

bays were unable to redistribute the loads, bringing down the interior structure below 

the east penthouse; and, 

• Horizontal progression of the failure across the lower floors (in the region of floors 5 

and 7, that were much thicker than the rest of the floors), triggered by damage due to 

the vertical failure resulting in disproportionate collapse of the entire structure. 

NIST has reviewed the fuel system for emergency power in WTC 7, which contained two 

independently supplied and operated fuel systems for emergency power. The two 

systems combined with all of the sub-systems, contained more than an estimated 43,000 

gal of fuel, assuming all tanks were filled near capacity. 
One of these systems (the base system) contained two 12,000 gallon (gal) storage tanks 

below the 1st floor loading dock. A duplex pump set on the 1st floor supplied fuel to a 

275 gal capacity day tank in the 5th floor Generator Room and to a 50 gal capacity 

engine-mounted day tank on the 9th floor. A second duplex pump set supplied fuel from 

these storage tanks to a 275 gal day tank on the 8th floor. A 6,000 gal above ground 

storage tank on the 1st floor connected to a second pump set supplied a 275 gal day tank 

on the 7th floor. The sub-systems that comprised the base system were similarly designed 

but were independently operated by the fuel pump set controllers for each system. 

 

The second fuel oil distribution system was supplied by two 6,000 gal storage tanks 

located under the loading dock. A duplex pump set on the 1st floor supplied fuel oil to 

nine generators on the 5th floor. Since there was already a day tank on the 5th floor 

associated with the base system and the New York City Building Code did not permit 

more than one day tank per floor, this system used a continuously pressurized fuel supply 

piping system without a day tank. 

Fuel oil piping systems like these are fairly common and are used to operate diesel 

generators and oil fired furnaces in many applications. The systems generally use day 

tanks located at the generators kept filled from remote storage tanks through transfer 

pumps and piping. The pipe-in-pipe design used in WTC 7 is quite robust and reliable in 

preventing leaking fuel from escaping the system. 

For the base system, mechanical equipment rooms were equipped with sprinkler systems. 

In addition, the fuel oil pump room on the first floor was protected with a sprinkler 

system. The 5th floor generator rooms did not contain an automatic fire suppression 

systems, but the generator rooms on the 8th and 9th floors were protected by sprinkler 

systems. The 7th floor generator room also did not contain a fire suppression system but 

did have smoke detectors. The 5th floor base system generator room appears to have been 

constructed of 8 inch thick concrete block. The other generator room enclosures were 

constructed using gypsum board. The first floor storage tank room was protected by an 

Inergen system and was enclosed in a 4-hour fire rated construction. 

 

One possibility being considered in the NIST working hypothesis is that the impact 

sustained by WTC 7 from the collapse of WTC 1 may have resulted in fractures in the 

fuel piping system (both the fuel pipe and the containment pipe) especially at the point 

where the pipes entered the valve box, which was rigidly mounted to the underside of the 

floor slab. With the base system and all of the modifications thereto, such a fracture 

would result in a small leak of residual fuel in the pipes at the point of fracture. A 

fracture of the pipe at the valve box would release fuel under pressure that, if ignited, 

could produce a spray fire and/or pool fire very near the critical columns that initiated a 

local failure at the lower floors of the building. 

Rupture of a day tank would release more fuel, but it would be contained by the overflow 

pan. Not until the generators ran long enough to drain the day tank to its low fuel level 

and bring on the transfer pumps would additional fuel and pressure in the transfer lines 
cause a more significant fuel leak. Depending on the number of generators connected to 

the day tank, this would require several hours. 

The pressurized system, which supplied the nine generators on the 5th floor, was 

different. If the supply or return pipes were fractured along with the containment pipe 

and the generators started, the fuel pipes would be continually pressurized, and any leak 

would continue until the storage tanks were empty as long as any one generator was 

running. 

NIST reviewed the report of an environmental contractor hired in the months after the 

collapse of WTC 7 to recover remaining fuel and mitigate any environmental damage 

from the second system’s two 6,000 gal tanks. The tanks were damaged and appeared to 

be empty and the report stated that neither the underground storage tanks nor their 

associated piping contained any residual petroleum product. No residual free product or 

sludge was observed in either underground storage tank. Evidence suggests that this fuel 

did not leak into the underground soil and contaminate it, and, therefore, could have been 

consumed in the building. 

In summary, NIST has presented a working hypothesis for the collapse of WTC 7 and 

fully documented the fuel systems present in the building on September 11, 2001. 

NIST’s investigation of the collapse of WTC 7 is continuing with a focus on identifying 

the factors that contributed to the collapse of the building. NIST has not reached a final 

determination on the role of the diesel fuel in sustaining the fires that burned in WTC 7 

and is continuing to study its role in contributing to the collapse of the building. 

Thank you. I will be pleased to answer any questions. 

(Appendix 1 – NCSTAR 1-1, Chapter 12, “WTC 7 Fuel System”) 

(Appendix 2 – NCSTAR 1-1J Chapter 2, “Fuel Oil Provisions of the BCNYC”) 
APPENDICES 
NIST NCSTAR 1-1, WTC Investigation 175

Chapter 12 

WTC 7 FUEL SYSTEM

World Trade Center (WTC) 7 was constructed and owned by Silverstein Properties (Silverstein) on land 

owned by the Port Authority of New York and New Jersey (Port Authority). It was built and operated by 

Silverstein as a Port Authority tenant alteration. Many of the tenants conducted critical business 

operations in the building and required uninterruptible power to prevent the loss of information or 

operational continuity in the event of a power failure. Backup power was provided by diesel generators 

located in the mechanical spaces of the building. These generators were designed to start automatically in 

the event of an interruption of the utility supply. The total generator capacity and quantity of fuel stored 

in the building was sized to tenant needs. 

12.1 CODE REQUIREMENTS 

Design and installation of the WTC 7 emergency power and associated fuel systems was consistent with 

the 1968 New York City (NYC) Building Code. The base system was installed in 1987 with 

modifications occurring in 1990, 1994, and 1999. Over the period 1987 to 1999, the NYC Building Code 

provisions discussed below were not changed, so all systems were installed to the same requirements. 

Some of the key code provisions for the construction and location of fuel storage tanks, piping, and 

controls are discussed here, and additional details are contained in NIST NCSTAR 1-1A. 

12.1.1 Tanks (27-828 and 27-829) 50

All tanks must be fabricated of steel and coated to prevent corrosion. Minimum thicknesses are specified 

by tank diameter for storage tanks and for so-called “day tanks” (60 gal or 275 gal). Large storage tanks 

(up to 20,000 gal) may be buried inside or outside the building or on the lowers floor of the building with 

protection related to the tank capacity. For example, tanks from 550 gal to 1,100 gal must be enclosed in 

2 h fire rated, noncombustible construction and tanks larger than 1,100 gal in 3 h construction. 

Tanks on floors above the lowest floor are limited to 275 gal and one such tank per story. These “day 

tanks” must be surrounded by a concrete curb or steel pan with the capacity to hold twice the volume of 

the tank in the event of a leak. The curb or pan must be provided with a float switch to sound an alarm 

and shut off the transfer pump in case of tank failure. Appropriate controls (generally a float switch in the 

day tank) must be provided to transfer fuel from the storage tanks to the day tank through a transfer pump 

and piping, with only one such transfer pump and piping network per day tank. 

12.1.2 Piping (27-830)37

Piping from transfer pumps to day tanks is required to be enclosed in a shaft of 4 in. thick concrete or 

masonry with a 4 in. clearance to the fuel pipe. Horizontal offsets may be enclosed in a steel sleeve two 

 

50 Sections of the NYC Building Code in which these requirements are found. These provisions are found in the subchapter on 

“Heating and Combustion Equipment.” 
Chapter 12 

176 NIST NCSTAR 1-1, WTC Investigation

(pipe) sizes larger and enclosed in 2 h fire rated construction. The spaces between the fuel pipe and 

sleeve or shaft must lead to an open sight drain or an open sump so leaks can be detected. 

12.1.3 Power Systems Designs 

National Institute of Standards and Technology (NIST) located and reviewed specifications and drawings 

for each of the emergency power systems. Some of the fuel risers were installed in existing shafts 

containing other utilities. The NYC Building Code requires that pipe shafts containing piping from the 

transfer pump to storage tanks above the lower floors not be penetrated by or contain other piping or ducts 

(27-830(f)(5)). Correspondence relating to the system for the Mayor’s Office of Emergency Management 

shows that this system was reviewed and inspected by the New York City Fire Department (FDNY), a list 

of needed corrections was produced, and each item was initialed as the corrections were verified. 

12.2 BASE BUILDING SYSTEM 

The initial base emergency power system was installed in 1987, and consisted of two 900 kW generators 

and a 275 gal day tank located on floor 5. Main fuel storage was in two 12,000 gal tanks buried under the 

loading dock on the south side of the building. The tanks were double wall fiberglass51 with leak 

detectors between the walls. 

Fuel was transferred by one of the two pumps through a 2 in. supply line in an existing shaft containing 

other utilities, near the west bank of passenger elevators. The transfer pump was controlled by a float 

switch in the day tank with a low (pump on) and a high (pump off) position. An alarm would be sounded 

if the fuel level in the day tank fell below the low level or went above the high level. The day tank was 

located within a 550 gal pan fitted with an alarm and another pump cutoff. The vent for the day tank 

terminated outside the south wall. 

The 2 in. fuel lines were encased in a second pipe covered with 2 in. of calcium silicate to provide the 

required 2 h fire rating. Pipe supports were located approximately 10 ft apart, and inspection plugs were 

provided approximately 50 ft apart. Mechanical equipment rooms were sprinklered (ordinary hazard 

group I), and the fuel pump room was sprinklered (ordinary hazard group III). The generator area on 

floor 5 was not sprinklered. 

12.2.1 Modifications to System 

From 1990 to 1999, four major modifications (additions) were made to the base emergency power 

system. These modifications are summarized in Table 12–1. Of significance are the 1990 modification 

(Salomon Brothers) that required a pressurized fuel supply system, because a day tank already existed on 

floor 5, and the 1999 modification (Mayors’ Office of Emergency Management) that required a separate 

6,000 gal tank on the first floor. Figure 12–1 is a schematic of the locations of the various components of 

the base system and the four major modifications. 

 

51 While the NYC Building Code requires steel tanks, effective in November 1985 the U.S. Environmental Protection Agency 

required (40CFR280) that all new underground fuel storage tanks be double wall fiberglass and that any steel tanks older than 

20 years be replaced by double wall fiberglass. 
 WTC 7 Fuel System 

NIST NCSTAR 1-1, WTC Investigation 177

For the Salomon Brothers system, the transfer pumps were powered from the output of the generators. In 

the event of a failure of utility power, all nine generators were started automatically to ensure that if any 

of the nine did not start there would be enough power. Once the generators were up to speed, the control 

system would shut down those that were not needed, but these could be restarted later if power demand 

increased. There was enough fuel and residual pressure in the lines to start the generators and to run them 

for a few minutes, but once running, the fuel pumps were powered to supply fuel. As long as any one 

generator was running, the pumps ran at full capacity. 

Table 12–1. Summary of modifications to base emergency power system in WTC 7. 

Year Day Tank/Generator Storage Tank Piping Comments 

1990 No day tank permitted since 

base design included one on 

floor 5/nine generators on 

floor 5, 1,750 kW combined 

capacity 

Two 6,000 gal next to 

base tanks. 

Two 21⁄2 in. pipes in 

separate rated shaft 

50 psi pressurized 

fuel system 

1994 50 gal/125 kW on floor 9; 

generator room sprinklered 

Used existing base 

tanks 

11⁄4 in. in new 2 h 

rated dedicated shaft 

New transfer pump 

connected to existing 

storage tanks 

1994 275 gal/350 kW on floor 8; 

generator room sprinklered 

Used existing base 

tanks 

2 in. in same 

dedicated shaft as 

above 

New transfer pump 

connected to existing 

storage tanks 

1999 275 gal/three 500 kW on 

floor 7; smoke detectors in 

generator room 

6,000 gal on floor 1, in 

4 h rated enclosure; 

gaseous (clean) fire 

suppression system; 

space below tank 

sprinklered 

10 gauge conduit in 

2 h rated enclosure 

Storage tank kept 

filled from base 

storage tanks. 
Chapter 12 

178 NIST NCSTAR 1-1, WTC Investigation

5TH FLOOR

4TH FLOOR

3RD FLOOR

2ND FLOOR

1ST FLOOR

DISTRIBUTION SYSTEM

BASE BULDING

9TH FLOOR

8TH FLOOR

6TH FLOOR

7TH FLOOR

AMERICAN EXPRESS

DISTRIBUTION SYSTEM

DISTRIBUTION SYSTEM

AMBASSADOR CONSTRUCTION

SALOMON BROTHERS

DISTRIBUTION SYSTEM

MAYOR'S OFFICE

DISTRIBUTION SYSTEM

(QTY. OF 2)

(QTY. OF 9)

(QTY. OF 3)

DAY TANK

STORAGE TANK

EMERGENCY GENERATOR

PUMP SET

LEGEND

Figure 12–1. Section plan showing the final locations of the fuel oil distribution 

components. 
 WTC 7 Fuel System 

NIST NCSTAR 1-1, WTC Investigation 179

12.2.2 Ambassador Modification 

The Ambassador modification to the base system was performed in 1994. A new transfer pump set 

(145 gph at 100 psi) was installed and connected to the existing main storage tanks. A new 11⁄4 in. supply 

riser was located in a new 2 h shaft dedicated for the fuel distribution system, constructed of 4 in. 

masonry and located at the south end of the center bank of passenger elevators. The line ran to a single 

125 kW generator with a 50 gal day tank mounted in a 100 gal basin on the 9th floor. Controls and 

alarms were the same as the base system. The transfer pipes were the same double wall design and, 

outside the masonry shaft, were covered with a 2 h vermiculite. The area of the generator on the 9th floor 

was sprinklered. No design criteria were located, but the pipe sizes for the entire 9th floor are consistent 

with a light hazard pipe schedule design. 

12.2.3 American Express Modification 

At about the same time in 1994, American Express installed a system to supply their operations. Another 

new pump set rated 170 gph (at 100 psi) was installed on the first floor and was tapped into the existing 

base system pipes and tanks. Another 2 in. supply pipe ran in the same masonry shaft used for the 

Ambassador system to a 275 gal day tank and a single 350 kW generator on the 8th floor. Controls and 

alarms were the same as the base system. The 8th floor generator room was protected with sprinklers 

designed to light hazard criteria. 

12.2.4 Mayor’s Office of Emergency Management (OEM) Modification 

In 1999, the Mayor’s Office of Emergency Management was constructed on the 7th floor. This system 

differed from the others because the specifications were to provide an independent source of power for 

full operations for at least one week, requiring the installation of a new, 6,000 gal storage tank and three 

500 kW generators fed from a single 275 gal day tank on the 7th floor. The main storage tank was 

located on the 1st floor of the building in an existing storage room adjacent to the elevators. The room 

was modified by installing a raised structure on which the tank was installed, enclosed in 4 h masonry 

(8 in. concrete masonry unit) construction. 

A new fill pump set rated 2,000 gph at a design pressure of 125 psi was located in the 1st floor pump 

room along with a transfer pump set rated 700 gpm at a design pressure of 125 psi. The 6,000 gal OEM 

tank was kept filled from the two 12,000 gal base system tanks by means of the fill pump. The 1st floor 

tank room was protected with an Intergen suppression system with the space below the tank still 

sprinklered (high hazard). The 7th floor generator room was not sprinklered but was protected by smoke 

detectors connected to the building alarm system. 

12.2.5 Salomon Brothers Emergency Power System 

In 1990 Salomon Brothers installed a system to provide emergency power to their trading floor that was 

independent from the other systems in the building. The Salomon Brothers system involved two 

6,000 gal tanks identical to and buried adjacent to the base system tanks under the loading dock on the 

south side of the building. Salomon Brothers had a contract with a fuel delivery service who always 
Chapter 12 

180 NIST NCSTAR 1-1, WTC Investigation

maintained the tanks full.52 Therefore, both tanks likely contained 6,000 gal of fuel on 

September 11, 2001. 

The system utilized nine generators on the 5th floor with a combined capacity of 1,750 kW. Seven 

cooling fan sets (four fans per set) were installed to provide cooling and combustion air to the generators. 

Three fan sets were installed on the north end of the east wall and four fan sets on the north end of the 

west wall. There were exhaust louvers on the south end of the west wall. These fans were arranged to 

come on when the generators were running. 

Since there was already a 275 gal day tank on the 5th floor associated with the base system, the New 

York City (NYC) Building Code did not permit another tank on that floor. The Salomon Brothers system 

was designed with a pressurized fuel system without a storage tank near the generators. Two 70 gpm at 

50 psi total head pumps were located in a separate enclosure in the existing fire pump room (not in the 

fuel pump room with the other transfer pumps). A double supply and return pipe (each 21⁄2 in. covered in 

2 in. of calcium silicate) were run in a separate shaft to the 5th floor where the pipes ran outside the 

mechanical room to the generators in three groups. At the end of the pipe run, where the fuel supply pipe 

ended and the fuel return pipe began, there was a valve box containing a backpressure regulator, gauges, 

and a by-pass line. This liquid tight valve box was mounted to the underside of the floor slab for the 

6th floor near generator #1. 

The transfer pumps were powered from the output of the generators. In the event of a failure of utility 

power, all nine generators were started automatically. This is to ensure that if any did not start there 

would be enough power. Once up to speed, the control system would shut down generators that were not 

needed, but they could be restarted later if demand increased. There was enough fuel and residual 

pressure in the lines to start the generators and to run them for a few minutes, but once running, the fuel 

pumps were powered to supply fuel. As long as any one generator was running, the pumps ran at full 

capacity. 

The system also included cooling fan units (each consisting of four fans) with three units (rated 

30,000 cfm per fan, 12 fans) installed in the northeast corner of the 5th floor near generators 1 through 4, 

six units (rated 38,000 cfm per fan, 24 fans) in the northwest corner near generators 8 and 9, and exhaust 

louvers in the southwest corner near generators 5 through 7. The fans were powered from the generators 

and ran whenever the generators were running. They brought outside air into the building and across the 

generators. 

12.3 POSSIBLE FAILURE MODES 

Fuel oil piping systems like these are fairly common and are used to operate diesel generators and oil 

fired furnaces in many applications. The systems generally use day tanks at the appliance kept filled from 

storage remote tanks through transfer pumps and piping. The pipe-in-pipe design used in WTC 7 is quite 

robust and reliable in preventing leaking fuel from escaping the system. 

At the time WTC 7 was designed and built there were no seismic design requirements for buildings in 

New York City much less for piping systems. More recent research into the failure of fire sprinkler 

 

52 Interview with Mike Catalano, maintenance person for Salomon Brothers, who was responsible for these systems. 
 WTC 7 Fuel System 

NIST NCSTAR 1-1, WTC Investigation 181

systems in earthquakes has resulted in seismic design requirements for critical piping systems in seismic 

zones. The research on sprinkler systems has shown the need for lateral bracing to prevent the failure of 

the piping systems due to differential movement between the pipes and the building in an earthquake. 

A working hypothesis is that the impact sustained by WTC 7 from the collapse of WTC 1 resulted in 

fractures in the fuel piping system (both the fuel pipe and the containment pipe) especially at the point 

where the pipes entered the valve box, which was rigidly mounted to the underside of the floor slab. With 

the base system and all of the modifications thereto, such a fracture would result in a small leak of 

residual fuel in the pipes at the point of the fracture. A fracture of the pipe at the valve box would release 

fuel under pressure that, if ignited, could produce a spray fire and/or a pool fire very near column 79. 

Rupture of a day tank would release more fuel, but it would be contained by the overflow pan. Not until 

the generators ran for long enough to drain the day tank to its low fuel level and bring on the transfer 

pumps would additional fuel and pressure in the transfer lines cause a more significant fuel leak. 

Depending on the number of generators connected to the day tank, this would require several hours. 

The Salomon Brothers pressurized system is different. If the supply or return pipes were fractured along 

with the containment pipe and the generators started, the fuel pipes would be continuously pressurized, 

and any leak would continue until the storage tanks were empty as long as any one generator was running. 

NIST reviewed the report of an environmental contractor (Langan 2002) hired in the months after the 

collapse of WTC 7 to recover remaining fuel and to mitigate any environmental damage from the 

Salomon Brothers tanks. The Salomon Brothers tanks were damaged and appeared to be empty, “ ... 

Neither the UST’s (underground storage tanks) nor their associated piping contained any residual 

petroleum product. No residual free product or sludge was observed in either UST.” 

The tanks were installed on a concrete slab over existing silty sand. A layer of bedding gravel on the slab 

provided a foundation for the tank. Examination of the gravel below the tanks and the sand below the 

slab showed some fuel contamination but none was observed in the organic marine silt/clay layer below. 

Also, the sand and soil below the slab was continuous below the adjacent base system tanks, which 

contained a total of 24,000 gal of fuel. Thus, it is likely that a fuel leak in any of the tanks would result in 

fuel contamination in this soil. 
Chapter 12 

182 NIST NCSTAR 1-1, WTC Investigation

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NIST NCSTAR 1-1J, WTC Investigation 3

Chapter 2

FUEL OIL PROVISIONS OF THE BCNYC 

The facilities of the Port Authority of New York and New Jersey (PANYNJ) are not subject to the 

requirements of the local building codes, although PANYNJ policy was to follow the New York City 

codes where applicable. The distribution system was to be designed to the provisions of the Building 

Code of the City of New York (BCNYC). As previously stated, the fuel oil distribution systems were 

installed in 1987 and 1990 with modifications occurring in 1994 and 1999. Generally, building 

construction is performed to the most current code provisions at the time of installation. The code 

provisions are often updated as technology and experience advance. However, between 1987 and 1999, 

the fuel oil system provisions of the BCNYC remained unchanged. Thus, a single set of code provisions 

can be summarized for the initial design and the subsequent modifications. The BCNYC code provisions 

used for the installations and modifications to the fuel oil distribution systems in World Trade Center 

(WTC) 7 are listed in the remaining sections of this chapter. 

2.1 GENERAL REQUIREMENTS 

The hydrocarbon fuel oil used shall be as classified in Reference Standards (RS) 14-3 and RS 14-12 and 

shall have a flashpoint not lower than 100 °F (27-827).1, 2

2.2 FUEL OIL STORAGE EQUIPMENT 

All fuel oil storage tanks shall be built of steel plates or sheets, made by the open hearth or basic oxygen 

process (27-828(a)(1)). 

Tanks shall be welded, riveted and caulked, or riveted and welded. Flanges or other pipe connections 

may be welded. Filler of any kind between plates shall be prohibited (27-828(a)(2)). 

Tanks to be buried shall be cleaned and then coated on the outside with two coats of red lead, or 

equivalent. Tanks shall be further protected by a coating of hot tar, asphalt, or equivalent rust resistive 

material, applied at the work site. Tanks installed inside buildings above ground shall be coated with one 

coat of red lead, or equivalent (27-828(a)(3)). 

All buried storage tanks shall be constructed of at least 1⁄4 in. thick metal and shall be designed to 

withstand any external loads to which the tank may be subjected (27-828(a)(4)). 

Shop fabricated storage tanks shall be installed without structural alteration (27-828(a)(5)). 

All openings shall be through the top of the storage tank (27-828(a)(6)). 

 

1

 The fuel oil used in WTC 7 was no. 2 fuel oil. 

2

 The BCNYC references given, denoted by 27-XXX, is the new numbering system. 
Chapter 2 

4 NIST NCSTAR 1-1J, WTC Investigation

Tanks for no. 2 commercial grade oils need not have manholes. However, if manholes are used for such 

oils, the manhole covers shall be bolted and made gastight (27-828(a)(7)). 

Tanks shall be located at least 7 ft, measured in the most direct manner, from any source of exposed flame 

unless protected as provided in 27-829(a)(2) or 27-829(a)(3) and at least 2 ft from any surface where the 

temperature exceeds 165 °F (27-828(a)(9)). 

Cylindrical tanks, except vertical tanks above ground outside of buildings, of more than 275 gal capacity 

shall be constructed as follows (27-828(b)): 

1. Tanks 36 in. in diameter and less – at least 1⁄4 in. shell and 1⁄4 in. heads. 

2. Tanks 37 to 72 in. in diameter – at least 1⁄4 in. shell and 5/16 in. heads. 

3. Tanks 73 to 120 in. in diameter – at least 5/16 in. shell and 3/8 in. heads. 

4. Tanks over 120 in. in diameter shall be of at least 3/8 in. steel and shall be stiffened by angle 

rings or equivalent members so as to retain their cylindrical form. 

All oil storage tanks of 275 gal capacity or less that are not buried shall have a minimum thickness of 

shell and head plates of no. 10 manufacturer’s standard gauge steel plate. Storage tanks of 60 gal capacity 

or less shall be similarly constructed but need not be thicker than no. 14 manufacturer's standard gauge 

(27-828(d)). 

2.3 LOCATION OF TANKS 

Inside of buildings, above ground, on the lowest floor as follows (27-829(a)): 

1. Storage tanks having a capacity of 550 gal or less may be installed above ground on the 

lowest floor of a building, provided that such tanks are mounted on adequate noncombustible 

supports, with the tank anchored thereto. No more than 550 gal of total storage capacity may 

be connected to one burner or may be installed without the protection provided in paragraph 

27-829(a)(2) or 27-829(a)(3). 

2. Storage tanks having a capacity of more than 550 gal but less than 1,100 gal may be installed 

above ground on the lowest floor of a building, provided that all portions of such tanks above 

the floor are completely enclosed with noncombustible construction having at least a 2 h fire 

resistance rating. Weep holes 1 in. in diameter shall be provided at least every 3 ft along the 

bottom of the enclosure unless at least 15 in. of clearance, together with access door, is 

provided between the tank and the enclosure. 

3. Storage tanks having a capacity of 1,100 gal or more may be installed above ground on the 

lowest floor of a building, provided that all portions of such tanks above the floor are 

completely enclosed with noncombustible construction having at least a 3 h resistance rating. 

At least 15 in. clearance shall be provided over the tanks and on all sides between the tanks 

and the enclosure. A noncombustible access door, constructed so as to preserve the integrity 

of the fire resistive enclosure, shall be installed in the enclosure above the point where the 
 Fuel Oil Provisions of the BCNYC 

NIST NCSTAR 1-1J, WTC Investigation 5

capacity of the enclosure below the door sill would be equal to the capacity of the largest tank 

installed. When the longest inside dimension of the enclosure exceeds 35 ft, access doors 

shall be installed at intervals not exceeding 12 ft. Columns, pipes, or similar obstructions 

may project into the required 15 in. of space within the enclosure, provided that access door 

or doors are so arranged that all portions of the enclosure are accessible for servicing. 

4. The capacity of individual storage tanks in no case shall exceed 20,000 gal. 

Inside of building above the lowest floor as follows (27-829(b)): 

1. Fuel oil storage tanks having a capacity of 275 gal or less may be installed inside of buildings 

above the lowest story when provided with a 4 in. thick concrete or masonry curb, or with a 

metal pan of gauge equal to the gauge of the tank, completely surrounding the tank and of 

sufficient height to contain two times the capacity of the tank. The number of such oil 

storage tanks shall be limited to one per story. 

2. Storage tanks having a capacity of 275 gal or less, installed above the lowest floor inside a 

building shall be filled by means of a transfer pump supplied from a primary storage tank 

located and installed as otherwise required. A separate transfer pump and piping circuit shall 

be provided for each storage tank installed above the lowest floor. No intermediate pumping 

stations shall be provided between the storage tank and the transfer pump. Appropriate 

devices shall be provided for the automatic and manual starting and stopping of the transfer 

pumps so as to prevent the overflow of oil from these storage tanks. 

3. A float switch shall be provided with the curb or pan around the storage tank and shall be 

arranged so as to sound an alarm and stop the transfer pump in case of failure of the tank or 

the control in the tank. The operation of the float switch shall be tested at least once each 

week. An alarm bell shall be located in the same room with the tank and a visual and audible 

alarm shall be located in a maintenance office. 

Inside of buildings, below ground as follows (27-829(c)): 

1. Storage tanks having a capacity greater than 275 gal may be buried inside a building provided 

that the top of the tank is at least 2 ft below floor level. In lieu of 2 ft of earth over the tank, 

the tank may be covered by concrete flooring having the same thickness as the basement 

floor, but not less than 4 in. concrete and reinforced with 2 in. by 2 in. mesh of at least no. 20 

U.S. standard gauge steel wire. Tanks shall be placed in firm soil and shall be surrounded by 

clean sand or well-tamped earth, free from ashes and other corrosive substances, and free 

from stones that will not pass through a 1 in. mesh. When necessary to prevent floating, 

tanks shall be securely anchored. 

2. No tank shall be buried within 3 ft of any foundation wall or footing. 

Outside of building, below ground as follows (27-829(d)): 

1. Storage tanks located outside of buildings and below ground shall be buried with the top of 

the tank at least 2 ft below ground. Tanks shall be placed in firm soil and shall be surrounded 
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6 NIST NCSTAR 1-1J, WTC Investigation

by clean sand or well-tamped earth, free from ashes or other corrosive substance, and free 

from stones that will not pass through a 1 in. mesh. When necessary to prevent floating, 

tanks shall be securely anchored. 

2. No tank shall be buried within 3 ft of any foundation wall or footing. 

2.4 PIPING 

Exposed piping shall be protected against mechanical damage and shall be adequately supported with 

rigid metal fasteners or hangers. All pipes connected to buried tanks, except test well piping, shall be 

provided with double swing joints at the tank (27-830(a)(1)). 

Only new wrought iron, steel, or brass pipe, or type K or heavier copper tubing, or aluminum alloy 

tubing, properly identified, may be used. Metal tubing when used for conveying oil shall be adequately 

protected. Such tubing may be installed at the burner without protection. Drawn tubing when used in 

domestic installations shall be of at least 3/8 in. inside diameter up to the shut-off valve at the burner. 

Soldered connections shall be prohibited (27-830(a)(2)). 

Overflow pipes, where installed, shall not be smaller in size than the supply pipe (27-830(a)(3)). 

Where a shut-off valve is installed in the discharge line from an oil pump, a relief valve shall be installed 

in the discharge line between the pump and the 1st shut-off valve (27-830(b)(1)). 

A relief or pressure regulating valve shall be provided in the oil piping system on the heater side of the 

shut-off valves (27-830(b)(2)). 

Relief valves shall be set to discharge at not more than one and one-half times the maximum working 

pressure of the system. The discharge from relief valves shall be returned to the storage tank or to the 

supply line. There shall be no shut-off valve in the line of relief (27-830(b)(3)). 

Fuel oil heaters shall not be installed within the steam or water space of a boiler. Fuel oil heaters and the 

connecting piping shall be arranged to prevent oil leakage from being transmitted to the boiler. This may 

be accomplished by any of the following methods (27-830(c)): 

1. By discarding the condensate from the heaters. 

2. By using approved double tube or other approved heaters. 

3. By means of a secondary hot water or steam heating system where the water or steam from 

the boiler has no direct contact with the oil heater. 

4. By a sight tank arrangement for collecting and inspecting the condensate which is provided 

with a pump controlled by a hand switch for returning the condensate to the normal return 

system. 

5. By such other method as may be permitted by the commissioner. 
 Fuel Oil Provisions of the BCNYC 

NIST NCSTAR 1-1J, WTC Investigation 7

A vent pipe of iron or steel, without trap, draining to the tank, shall be provided for each storage tank. 

The lower end of the vent pipe shall not extend more than 1 in. through the top of the storage tank. Crossconnection between a vent pipe and fill pipe is prohibited (27-830(d)(1)). 

Where a battery of storage tanks designed to hold the same grade of oil is installed, vent pipes may be run 

into a main header (27-830(d)(2)). 

Vents shall be at least one and 1⁄4 in. in diameter for storage tanks not exceeding 1,100 gal capacity and at 

least 2 in. in diameter for storage tanks of 1,100 gal or more except that vents for storage tanks of 60 gal 

capacity or less shall be at least 1⁄2 in. in diameter. Vents for tanks inside of buildings above the lowest 

floor shall be run into the primary storage tank vent (27-830(d)(3)). 

Vent pipes shall be provided with an approved weatherproof hood having a free area of at least the pipe 

size area. Vent pipes shall terminate outside the building in a non-hazardous location, at least 2 ft from 

any building opening and not less than 2 ft nor more than 12 ft above the fill pipe terminal, unless 

otherwise permitted by the commissioner. If the vent pipe terminal is not visible from the fill pipe 

terminal location, a 1 in. tell-tale line shall be connected to the tank and shall parallel the fill pipe and 

terminate at the fill pipe terminal with an unthreaded end. Such tell-tale lines shall be provided with a 

check valve set to prevent flow of surface water to the storage tank (27-830(d)(4)). 

Fill pipes shall terminate outside the buildings, with the fill pipe terminal located at or above grade, at 

least 2 ft from any building opening and 5 ft from any subway grating at or below the level of the fill pipe 

terminal. No fill pipe shall be less than 2 in. in diameter. Where there are facilities for the delivery tank 

truck to drive onto the premises, the fill terminal may be located elsewhere than at the curb 

(27-830(e)(1)). 

Each storage tank shall be provided with a separate fill pipe, except that where a battery of tanks is 

installed containing the same grade of oil, a common fill and header pipe may be installed (27-830(e)(2)). 

Where the top of the storage tank is above the fill pipe terminal, the fill pipe shall be connected to the top 

of the tank and provided with a shut-off valve and swing check valve both of which shall be located at the 

fill pipe terminal. However, the shut-off and check valves may be installed in an accessible location 

inside the building at or below the level of the fill pipe terminal (27-830(e)(3)). 

All fill pipe terminals shall be of an approved type, and shall be provided with lugs for embedding in 

concrete. In lieu of lugs, a set screw or threads to fasten the terminal to the fill pipe may be used 

(27-830(e)(4)). 

Piping from transfer pump to storage tanks above the lowest floor as follows (27-830(f)): 

1. The piping from a transfer pump to storage tanks at levels above the lowest floor in buildings, 

the return piping, and vent piping shall comply with the applicable provisions of subdivisions 

27-830(a) and 27-830(d) and shall be enclosed in a shaft constructed of 4 in. concrete or 

masonry having a 4 in. clearance from all pipe or pipe covering. Provision shall be made for 

expansion in piping without the use of expansion joints. 
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8 NIST NCSTAR 1-1J, WTC Investigation

2. Where it is necessary to make horizontal offsets in the supply piping and pipe shafts such 

piping shall be enclosed in a sleeve of other piping of at least no. 10 manufacturer's standard 

gauge steel, two sizes larger and arranged to drain into the shaft. Horizontal piping offsets 

shall be further enclosed in construction having a 2 h fire resistance rating. 

3. A drain pipe shall be installed at the base of shafts enclosing the supply and overflow piping. 

The pipe shall lead to an open sight drain or to an open sump. 

4. Oil lines for tanks above the level of the lowest floor shall be seamless steel pipe of a weight 

not less than ASA schedule 40 with welded connections. 

5. Pipe shafts shall not be penetrated by or contain other piping or ducts. 

The heating of oil in storage tanks shall be by means of coils using low pressure hot water or steam, or by 

means of electric heaters approved for use in oil storage tanks (27-830(g)). 

Where more than one storage tank is connected to a common supply line, a shut-off valve shall be 

provided in the supply line at each tank. Where more than one burner is connected to a supply line a shutoff valve shall be provided at each burner. Where a single tank and a single burner are installed, a shutoff valve shall be required in the supply line at the tank and another at the burner. Valves shall be brass 

or equivalent in corrosion and fire resistance, shall provide tight shut-off, and shall be rated at 125 psi or 

greater as required by the pressure in the system (27-830(h)(1)). 

Where a storage tank is located so that the top of the tank is above the oil inlet to the burner or to the fuel 

pump, and the storage tank capacity is greater than 275 gal, the supply line to the burner shall be provided 

with an approved anti-syphon device. The device shall be located at the highest point in the supply line. 

Where an approved foot valve is used in the tank and the tank is constructed with a manhole, an antisyphon device shall not be required (27-830(h)(2)). 

The pressure in oil lines to burners located above the lowest floor of a building shall not be more than is 

required to circulate oil to and from the burners, and all parts of the oil system shall be capable of 

withstanding the maximum working pressure in that part of the system (27-830(h)(3)). 

A remote control shall be provided to stop the flow of oil to any burner. Such control shall be located 

outside the entrance to the room in which the burner is located and as close to such entrance as 

practicable, except that when an outside location is impracticable, such control may be located 

immediately inside the room in which the burner is located, provided such location is accessible at all 

times. On storage tanks of 60 gal or less capacity used with manually operated burners, such remote 

control may be installed in the supply lines between tank and burner (27-830(h)(4)). 

Pressure in a storage tank for the purpose of discharging oil shall be prohibited (27-830(h)(5)). 

In systems where either steam or air is used for atomizing the oil, the oil and the atomizing supply shall 

be interlocked so that where the supply of either is interrupted, the supply of the other will be 

immediately cut off (27-830(h)(6)). 
 Fuel Oil Provisions of the BCNYC 

NIST NCSTAR 1-1J, WTC Investigation 9

All tanks located inside buildings shall be provided with an oil level indicating device. Test wells shall be 

prohibited in tanks located inside of buildings. Unused tank openings shall be permanently sealed to 

prevent the removal of plugs or cover (27-830(i)(1)). 

Oil level indicating devices shall be designed and constructed of substantial materials so that there can be 

no leakage of oil or oil vapor (27-830(i)(2)). 

Test wells in storage tanks located outside of buildings shall be capped oil tight and kept closed when not 

in use (27-830(i)(3)). 

2.5 CONTROLS 

With each automatic burner a set of safety controls of the electric, pneumatic, hydraulic, or mechanical 

type shall be installed and maintained in good working order. The controls shall provide the following 

functions (27-831): 

1. Ignition 

2. Stack or combustion control 

3. High temperature or pressure control 
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