Canadian Consulting Engineer

Storing flammable and combustible liquids; A

May 1, 2000
By R.P. Benedetti, National Fire Protection Association

A new edition of National Fire Protection Association (NFPA) 30, Flammable and Combustible Liquids Code, is being proposed for adoption at the NFPA 2000 World Fire and Safety Congress in Denver, Color...

A new edition of National Fire Protection Association (NFPA) 30, Flammable and Combustible Liquids Code, is being proposed for adoption at the NFPA 2000 World Fire and Safety Congress in Denver, Colorado in May. The new edition incorporates a number of changes that improve on the current 1996 edition. The most important are as follows.

Tank Storage. Chapter 2 has had a complete editorial overhaul so code requirements appear in a more logical fashion. In previous editions of the code, aboveground tanks, underground tanks, and tanks inside buildings were addressed independently, and consequently some requirements that were essentially identical were repeated.

The proposed 2000 edition treats design elements for all tanks first, followed by installation requirements, testing requirements, fire protection requirements, and finally, operations and maintenance requirements. Now, a designer might only need to refer to the first two major sections of the chapter, regardless of the type of tank. Likewise, plan reviewers and code compliance officers, who typically focus on installation and testing requirements, need only to refer to those sections.

The most significant technical change is the addition of requirements for vaulted, fire resistant, and protected aboveground tanks. These tanks provide enhanced response to an external fire and were allowed by NFPA 30A, Automotive and Marine Service Station Code, since the 1990 edition, although siting requirements were much more conservative than those in NFPA 30. While facilities under the scope of NFPA 30 could use these tanks, no credit was given for their enhanced fire resistance.

NFPA 30 now includes installation requirements for these tanks, with reduced separation distances allowed. It also gives reference to appropriate design standards for both fire resistant tanks and for protected tanks.

Another addition is the requirements for equipment and piping located in a diked area or in a remote impoundment basin. Product, utility, and fire protection system piping routed through a dike or remote impoundment must be directly connected to the tanks in that area; the piping cannot just be “passing through” on the way to another location. Equipment such as pumps and process equipment must be either located or protected so that a fire originating in the equipment does not pose a threat to tanks or piping. Hose connections and fire protection system control valves must be located outside the diked or impoundment area, allowing them to be accessible without putting fire fighting personnel at risk. These requirements are basic good fire protection and are flexible enough to allow some latitude in compliance.

Piping Systems. Chapter 3 has also been reorganized and editorially improved. There are two significant and related technical changes. Pipe joints that are mechanically fastened (as contrasted with welded, flanged, or screwed joints) can now be used, as long as the mechanical strength and integrity of the connection is not impaired when exposed to fire. And, pipe joints that depend on the frictional character of one or more components are now allowed, with specific restrictions. Hitherto, such joints were prohibited, but evidence has shown that certain types used in the specialty chemicals and semiconductor industries are considerably more reliable than other designs. The relevant sections of Chapter 3 have been revised to allow such joints if they can meet the stated performance requirements.

Secondary containment and double-wall piping is being used more frequently in underground installations, but previously Chapter 3 did not provide guidance for tightness testing of the outer containment. Consistent with the changes made to Chapter 2 for secondary containment-type tanks, Chapter 3 has added specific guidance for testing such piping.

Container and Portable Tank Storage. In 1996, the Technical Committee on Storage and Warehousing of Containers and Portable Tanks developed a set of mandatory fire protection system design criteria for storage of protected liquids. These criteria are in Section 4-8 of NFPA 30 and are based on full-scale fire tests that used representative flammable and combustible liquids in various types of containers and stored in different rack and palletized storage arrays. Some of this research was conducted by the Fire Protection Research Foundation (formerly the National Fire Protection Research Foundation); other research was conducted by individual companies and by consortia. Research continues today in an effort to expand the guidance given in Chapter 4 of NFPA 30.

The design criteria in the 1996 edition apply almost exclusively to metal containers of flammable and combustible liquids. The criteria covers water and foam-water sprinkler protection of palletized, rack, and shelf storage of liquids. There is one data set for plastic containers and this is limited to Class IIIB liquids — flash point *200F (*93C). The 2000 edition will include additional design criteria, particularly for water miscible liquids and for liquids packaged in rigid non-metallic intermediate bulk containers (IBCs). It will also include simplified design criteria for Class IIIB liquids in plastic containers up to 19 litres capacity.

One other major improvement: the requirements for spill containment and drainage have been integrated with the fire protection design criteria in section 4-8. Previously, these requirements were in a separate section and it was not always obvious to the user that they worked hand-in-glove with the protection design. Containment and drainage requirements for unprotected or sub-standard protection situations have been simplified as well.

Operations (Heat Transfer Systems, etc.). Probably the most significant new addition to the operations-related requirements of NFPA 30 is a new section in Chapter 5 addressing re-circulating heat transfer systems that use a heat transfer fluid flowing in a closed loop system. Prompted by more than 50 fire and explosion losses over the past 10 years, the new section provides for system design features, burner controls and interlocks, and piping system requirements to minimize the potential for fire and explosions. Automatic sprinkler protection (NFPA 13: Extra Hazard – Group 1) is mandatory for the system heater or vaporizer. Provisions are included for safe venting of the system’s over-pressure relief devices and for draining the system.

A new section addressing solvent distillation units has also been added to Chapter 5. Here is an example of NFPA 30 addressing a fire problem that has its origins in environmental protection. As the cost of handling hazardous waste has escalated, it has become cost-effective to recover used process solvents and fluids right on site, and small distilling units have been designed that neatly fill this need. The new section applies to units that do not exceed 227 litres (60 gallons) capacity and are used to process liquids up to 200F (93C) flash point. Such units are required to be listed in accordance with UL 2208, Standard for Solvent Distillation Units.

Electrical Equipment and Installations. Under the direction of the Technical Committee on Operations, all requirements for electrical system wiring and utilization equipment and for the classification of hazardous location areas have been consolidated into a single new chapter, Chapter 6. In addition, the “zone” concept of area classification is now recognized by NFPA 30. This will benefit the users who are now using the zone concept as an alternative to the class/group/division method.

NFPA 30A, Automotive Service Stations. In a related area, a new edition of NFPA 30A, Automotive and Marine Service Station Code, is proposed for adoption in Denver. This code has also undergone substantial editorial amendments, primarily to comply with NFPA style and also to expand coverage to all vehicle fueling regardless of the type of fuel. The title will be changed to reflect the broadened scope of the document: Code for Motor Fuel Dispensing Facilities and Repair Garages.

The most significant te
chnical change to NFPA 30A is a new chapter covering the dispensing of gaseous vehicle fuels. The intent of the new chapter is to address service stations that dispense compressed natural gas (CNG), liquefied natural gas (LNG), and liquefied petroleum gas (LPG) along with the usual gasoline and diesel fuel. Note that a service facility that dispenses only gaseous fuels is outside the scope of NFPA 30A and is addressed by NFPA 52, Standard for Compressed Natural Gas (CNG) Vehicular Fuel Systems, NFPA 57, Standard for Liquefied Natural Gas (LNG) Vehicular Fuel Systems, or NFPA 58, Liquefied Petroleum Gas Code.

Installation of the components of a CNG, LNG, or LPG fuelling systems is covered by the standards cited above and these are appropriately referenced in the new chapter. Listed dispensing devices are required, as are protective means to prevent uncontrolled flow if the dispenser is dislodged, for example in a vehicle collision. Such means would be similar to the shear valve underneath a gasoline or diesel fuel dispenser. Separation of above-ground storage tanks for gaseous fuels from property lines, public ways, and buildings on the same property must meet the criteria of NFPA 52 or NFPA 58. In addition, such tanks must be at least 15 metres (50 feet) from any dispensing device, gas or liquid.

Where CNG or LNG dispensing devices are located beneath a canopy or enclosure, the latter must be designed to prevent it trapping and collecting released natural gas, which is less dense than air and therefore rises. Alternatively, any electrical equipment or wiring present must be suitable for class I, division 1 locations.CCE

R. P. Benedetti, CSP is a senior flammable liquids engineer with the National Fire Protection Association of Quincy, Massachusetts.

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