Safety
Navigating NFPA
Codes and Standards
Jeremy Lebowitz, P.E.
Rolf Jensen & Associates, Inc.
Follow the recommendations and how-to guidance
provided by the National Fire Protection Association
to safeguard against fires and explosions.
T
he National Fire Protection Association (NFPA) has
developed and published more than 300 codes, standards, recommended practices, and guides intended
to minimize the possibility and effects of fire and related
risks. Virtually every building, process, service, design, and
installation in society today is affected by NFPA recommendations. The chemical process industries (CPI) are
particularly impacted by the safety measures contained in
the NFPA codes and standards.
A code is a set of rules put forth as recommendations. It
is not a law but can be adopted into law. A standard is a more
detailed elaboration of a code, and gives the nuts and bolts
of how to follow the code.
The NFPA develops codes and standards via a consensus
approval process, which requires input from users, code
enforcement officials, and special experts. The codes in
effect today reflect developments that have taken place over
several decades, including lessons learned from tragic events
resulting in casualties and/or significant property loss.
This article briefly discusses some of the basic NFPA
codes and standards that apply to general building design and
construction. Then, it explores in more depth the key NFPA
documents that apply to chemical processing facilities.
Building-construction standards
Many of the NFPA standards are designed as how-to
guides to assist property owners and tenants in installing
fire protection systems. Typically, the building code of the
local jurisdiction dictates which buildings require sprinklers and fire alarms. (The building code may be based on
the International Building Code or NFPA 5000, Building
Construction and Safety Code). Once it has been determined that a certain fire protection system is required, the
appropriate NFPA standard can be consulted to identify
18 www.aiche.org/cep May 2012 CEP
installation, testing, and maintenance requirements.
This section summarizes some of the major NFPA
building standards. While chemical engineers generally do
not need to deal with these codes and standards, this brief
overview can serve as a general reference, as these documents may dictate where and why certain major fire protection systems are required for a given process.
Uniform Fire Code (NFPA 1). NFPA 1 is a model fire
code that is adopted by fire departments of some jurisdictions
(the International Fire Code is adopted in other locations).
In jurisdictions that have adopted this code, it is generally
enforced by the local fire official. The intent of NFPA 1 is
to safeguard life and protect property from fire, explosion,
and other dangerous conditions. This code provides valuable
guidance on how to protect facilities from the dangers associated with specific hazardous materials, and references many
of the other codes and standards discussed in this article.
Where adopted, NFPA 1 is often the document that mandates
compliance with these other codes and standards.
Standard on the Installation of Sprinkler Systems
(NFPA 13). This standard explains the nuts and bolts
of designing and installing complete sprinkler systems,
including guidance on pipe sizing, seismic bracing, and
sprinkler selection. Another important parameter covered
in NFPA 13 is the quantity of water required to control fires
based on the type of chemical involved. For flammable and
combustible liquids, NFPA 30 (discussed later) provides
more detailed water-flow requirements.
National Fire Alarm and Signaling Code (NFPA 72).
This document governs the design and installation of fire
detection and alarm systems, as well as emergency communications systems (ECS; also commonly referred to as mass
notification systems or emergency voice/alarm communication systems). An ECS, a recent addition to NFPA 72,
Copyright © 2012 American Institute of Chemical Engineers (AIChE)
Division 1
(5-ft Radius)
Division 2
(10-ft Radius)
Vent
Separator
Exhauster
Bin
Hot Air
Class I, Division 1
Elevator
Feed
Class I, Division 2
p Figure 1. NFPA 70 provides guidance on the use and storage of
flammable and combustible liquids in classified locations such as this one.
Here, a product dryer handling a solid that is wet with a flammable liquid
is located in an adequately vented building.
Flammable and combustible liquids
The Flammable and Combustible Liquids Code
(NFPA 30) is arguably the most important NFPA code
for chemical engineers. The purpose of NFPA 30 is to
provide fundamental safeguards for the storage, handling,
and use of flammable and combustible liquids.
A liquid is considered combustible if it has a flashpoint
of 100°F (37.8°C) or higher; flammable liquids are those
with a flashpoint below 100°F. The flashpoint is the lowest temperature at which the vapor above the liquid surface
is ignitable. Flammable liquids are more hazardous than
combustible liquids, because an ignitable vapor concentration can arise above these liquids at temperatures near room
temperature. Combustible liquids are less hazardous because
significant heating can be required to achieve a concentration that renders the vapor above the liquid ignitable.
However, combustible liquids can be just as dangerous as
flammable liquids if heated above their flashpoints.
Flammable liquids are further categorized based on
flashpoints and boiling points into Classes IA, IB, and
IC; combustible liquids are categorized by flashpoint into
Classes II, IIIA and IIIB (Table 1). Note that the designations for hazardous locations that require classified electrical equipment use similar nomenclature, but area classification is different from the classification of flammable and
combustible liquids.
NFPA 30 provides specific guidance on how to protect
facilities from the hazards associated with flammable and
combustible liquids, in containers ranging from pint-sized
jars to million-gallon aboveground tanks. NFPA 30 specifies several key protection features for the storage and use
of these liquids inside buildings.
Size and location of storage rooms. A liquid storage
space can be designated a control area, a liquid storage
room, or a liquid warehouse, depending on the overall quantity of the liquid stored in it. The amount of liquids that may
be housed in each type of space is lowest in control areas
and highest in liquid warehouses, as is the stringency of the
requirements for protective features.
Control areas are rooms, floors, or portions of a building
is extremely valuable for quickly disseminating information to large populations. An ECS can prove immensely
beneficial in chemical facilities, especially those that are
sparsely populated, and where the installation of traditional
fire alarm systems can be cost-prohibitive or could fail to
convey sufficient information.
National Electrical Code (NFPA 70). The purpose of
the National Electrical Code (NEC) is to safeguard people
and property from the hazards of electricity. Of principal
importance to chemical engineers is Article 500, which
discusses electrical and electronic equipment located
in classified (hazardous) areas (1). The requirements in
Article 500 of the NEC apply to equipment located in
areas where flammable vapors (Class I), combustible dusts
(Class II), or combustible fibers (Class III) are anticipated, for both Division 1 (the hazard is present during
normal, routine operation) and Division 2 (the hazard can
occur only during abnormal process conditions, including
maintenance). The purpose of this part
Table 1. Flammable and combustible liquids can be further divided into classes.
of NFPA 70 is to reduce the risk of the
Liquid Classification
Flashpoint
Boiling Point
Examples
electrical equipment serving as the ignition source for hazardous materials (2).
Class IA — Flammable
<73°F (22.8°C) <100°F (37.8°C) Ethyl Ether, Pentane
Guidance is available for delineation
Class IB — Flammable
<73°F (22.8°C) >100°F (37.8°C) Ethanol, Acetonitrile,
of hazardous locations for flammable
Acetone, Toluene
vapors (NFPA 497) and combustible
Class IC — Flammable
>73°F (22.8°C)
All
Xylenes
dusts (NFPA 499). Figure 1 shows an
Class II — Combustible
>100°F (37.8°C)
All
Diesel Fuel, Hydrazine
example of a classified location housing
>140°F (60°C)
All
Aniline, Cyclohexanol
Class IIIA — Combustible
a flammable liquid process. Reference 3
Class IIIB — Combustible
>200°F (93°C)
All
Diethylene Glycol,
provides guidance on selecting motors
Motor Oil
for use in classified areas.
Copyright © 2012 American Institute of Chemical Engineers (AIChE)
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Safety
that are separated from other control areas and the rest of
stored in basements. The rationale for this requirement is
the building by fire-resistance-rated construction. Liquids
twofold: Heavier-than-air flammable vapors can accumuare heavily restricted in control areas, and as such there are
late in pits or sumps and pose a significant hazard to floors
no limitations on the size of the room. The amount of flamabove the basement; and, firefighter access is more chalmable and combustible liquids stored or handled in control
lenging on floors below grade. This requirement is more
areas cannot exceed the specified maximum allowable
stringent than the MAQs for below-grade control areas,
quantities (MAQs) in Table 2. Note that MAQs also apply
which still apply to other classes of hazardous materials.
to other classes of hazardous materials, such as oxidizers,
(In jurisdictions that enforce the 2006 and later editions of
flammable solids, and corrosive materials, through buildthe International Fire Code, small allowances exist for the
ing code requirements. The MAQs for hazardous materistorage and use of flammable liquids in basements.)
als located on floors above and below
Table 2. The amounts of flammable and combustible liquids that can be stored in
grade are lower than the MAQs for
control areas are restricted based on maximum allowable quantities (MAQs).
ground-level spaces, as firefighter access
Liquid Class
MAQ
becomes more difficult (Table 3).
1,2
Flammable
Liquids
30
gal
(115 L)
IA
Liquid storage rooms can contain
1,2
1,2
more flammable and combustible liq120 gal (460 L)
IB and IC
uids than are permitted in control areas.
IA, IB, IC (combined)1,2,3
120 gal (460 L)
Liquid storage rooms are limited to an
1,2
Combustible Liquids
120 gal (460 L)
IIA
area of 500 ft2 and must be separated
1,2
IIIA
330 gal (1,265 L)
from the rest of the building by fire1,2,4
13,200
gal (50,600 L)
IIIB
resistance-rated construction (1- or 2-h
Notes:
fire barriers, depending on room size).
1. Quantities can be increased by 100% if the materials are stored in approved flammable-liquids
The MAQs for flammable and combusstorage cabinets or in safety cans in accordance with the fire code. Where Note 2 also applies, the
tible liquids do not apply to liquid storincreases can be applied accumulatively.
age rooms; rather, flammable and com2. Quantities can be increased by 100% in buildings equipped throughout with an automatic sprinkler system installed in accordance with NFPA 13. Where Note 1 also applies, the increases can be
bustible liquid storage may not exceed
applied accumulatively.
a certain density, which can be up to 10
3. Quantities cannot exceed the maximum allowable quantity per individual control area for Class IA,
gal of liquid per square foot of storage
Class IB, or Class IC flammable liquids, individually.
room area. The maximum allowable
4. Quantities are not limited in a building equipped throughout with an automatic sprinkler system
installed in accordance with NFPA 13.
densities of flammable and combustible
liquids in these areas depend on room
size and the presence of automatic fire
Table 3. The MAQ for all hazardous materials is reduced for floors above and
below grade because firefighter access to those areas is more difficult.
suppression systems; densities are lower
for smaller rooms and rooms without
MAQ per
Number of
Number of
Control Area*,
Control Areas
Fire-Resistance
automatic fire suppression systems.
Floors
Above
or
%
of
GradeAllowed
per
Rating for Fire
Liquid warehouses, unlike the other
Below Grade
Level MAQ
Floor
Barriers‡, h
designated liquid storage areas, are
Above
>9
5
1
2
permitted to store unlimited quantities
Grade
7–9
5
2
2
of flammable and combustible liquids
as long as these areas are substantially
4–6
12.5
2
2
separated from occupiable buildings and
3
50
2
1
property lines (a 4-h-rated fire wall is
2
75
3
1
required if the warehouse is attached to
1
100
4
1
or within 10 ft of another building). LiqBelow
1
75
3
1
uid warehouses are not limited in area.
Grade
It should be noted that additional build2
50
2
1
ing code requirements apply to liquid
>2
NA
NA
NA
storage rooms and liquid warehouses,
NA = Not Allowed
which are not addressed in this article.
* Percentages represent the MAQ per control area shown in NFPA 30, Table 9.6.1, with all of the
One notable provision of NFPA 30
increases permitted in the footnotes of that table.
‡ Fire barriers must include floors and walls as necessary to provide a complete separation from
that applies to all storage room designations is that flammable liquids cannot be other control areas.
20 www.aiche.org/cep May 2012 CEP
Copyright © 2012 American Institute of Chemical Engineers (AIChE)
Container and quantity limitations. As noted earlier,
MAQs apply to control areas, and storage densities apply to
liquid storage rooms. To limit the amount of flammable or
combustible liquid that could be involved in a spill, limit­
ations also apply to container sizes.
Containers that are brittle or subject to damage under
fire conditions (e.g., glass, plastic) are either prohibited for
certain materials, or are limited in size. For example, the
maximum allowable size of a glass container for a Class IB
flammable liquid is 1 quart (1 L), whereas the maximum
size for Class IIIA combustible liquids is 5.3 gal (20 L).
Approved portable metal tanks and intermediate bulk containers (IBCs) up to 793 gal (3,000 L) may be used to store
flammable or combustible liquids in any class.
Fire protection system design. NFPA has carried out
significant research on the suppression of fires involving
flammable and combustible liquids, and the requirements
for fire protection systems for the storage of these liquids
are highly detailed — above and beyond the scope of
NFPA 13. Given the specific nature of these hazards, the
prescribed protection criteria are contained in NFPA 30 and
referenced by NFPA 13. Sprinkler design criteria are available for numerous storage configurations, including in-rack
storage and palletized storage of drums, with protection by
ordinary sprinkler systems as well as foam-water suppression systems.
Several factors must be taken into account to properly
design a sprinkler system for a space where flammable and
combustible liquids are stored:
• sprinkler system type (water spray or foam-water spray)
• container material (metal or nonmetal)
• container relief system (relieving or nonrelieving)
• miscibility of liquid in water
• storage configuration (rack, shelf, stack, or pallet)
• details of storage configuration (e.g., for rack storage,
single-, double- or multiple-row racks; widths of racks,
aisles and flue space width between racks)
• storage height
• ceiling height
• separation between racks or piles.
These factors will determine how much water is required
from the ceiling (and possibly in-rack) sprinklers, which in
turn dictates sprinkler and pipe sizes.
Electrical classification. Using electrical equipment that
is designated for classified (hazardous) locations is a key
measure to reduce the ignition hazards in a facility that handles flammable or combustible liquids. NFPA 30 provides
specific guidance for flammable liquid storage and processing areas that require electrically classified equipment.
For example, the inside of flammable liquid storage
rooms should carry a Class I, Division 2 electrical classification; in rooms that dispense flammable liquids, Class I,
Copyright © 2012 American Institute of Chemical Engineers (AIChE)
Division 1 electrically classified equipment should be used
within 3 ft of any vent and fill openings. See Ref. 2 for more
detailed information on electrical classification and the selection of equipment for use in such areas.
Containment, drainage, and spill control. A major
concern with flammable and combustible liquid fires is that
the pool of burning liquid could spread and involve other
containers, possibly initiating a chain reaction. This scenario
can quickly overwhelm a facility’s sprinkler system.
This threat can be mitigated to some extent with spill
control devices, such as berms, curbs, trenches, or spot drains.
Spill control is required in facilities utilizing flammable and
combustible liquid containers larger than 10 gal.
Another concern is that many of these liquids are less
dense than water, so the fire suppression water could carry the
burning liquid into unaffected areas. Additionally, this runoff
could enter public waterways, sewers, or adjoining properties. For these reasons, NFPA requires secondary containment
(possibly via an underground tank) and/or drainage to a safe
location. Drainage systems should have the capacity to handle
the expected discharge rate of fire suppression system water.
One way to reduce the size of secondary containment
systems is to install a foam-water system, which is designed
to suppress — i.e., extinguish — the fire. Traditional
sprinkler systems are designed to control a fire, keeping fire
growth in check until firefighters respond to extinguish the
fire. Hence, water flows and durations required for foamwater suppression systems can be substantially less than a
comparable water-only sprinkler system.
Explosion control. NFPA 30 requires explosion control
where Class IA flammable liquids are stored in containers
larger than 1 gal (4 L), due to the higher risk of flammable
vapors existing under normal operating conditions. Any of
the methods outlined in NFPA 69 (discussed later) can be
used for explosion control.
Ventilation. Flammable and combustible liquids in storage, and especially in use, can continually liberate flammable vapors. Without sufficient ventilation, these vapors
can accumulate to ignitable concentrations.
Ventilation should be provided at a minimum rate of
1 cfm per square foot of room area. Equally critical is the
location of ventilation supply and exhaust registers — vents
should be located within 12 in. of the floor and/or ceiling
(depending on whether the expected vapors are heavier or
lighter than air), and on opposite sides of the room to promote dilution and removal of flammable vapors.
Laboratory standards
The Standard on Fire Protection for Laboratories Using
Chemicals (NFPA 45) applies to small facilities such as
university laboratories and pilot-scale operations. The
primary focus of NFPA 45 is the subdivision of laboratory
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Safety
buildings into laboratory units, which are classified based
on the amounts and relative hazards of the chemicals contained therein. The approach is similar to, and often used
in conjunction with, the control area approach outlined
in NFPA 30. The requirements of the user (e.g., laboratory researcher, pilot plant engineer, etc.) typically dictate
which laboratory unit the facility falls into, ranging from
Class A (high fire hazard) to Class D (minimal fire hazard).
Table 4 provides specific laboratory unit designations
contained in NFPA 45. Many chemical users who handle
restricted amounts of flammable and combustible liquids,
such as those working in a laboratory or university setting,
fall into Class C Laboratory Unit.
NFPA 45 details the fire protection features required
for each laboratory unit based on its classification. Size
limitations, fire-resistance-rated construction, fire protection systems, and even explosion protection systems may be
required, depending on the hazard posed by each lab unit.
NFPA 45 is particularly valuable when considering ventilation systems for hoods and rooms, as the specific design
requirements permit many heating, ventilation, and air
conditioning (HVAC) features utilized in “green” building
design (e.g., heat recovery, air recirculation, and manifolding) while still providing for a fire-safe exhaust system.
Perchloric acid handling presents unique protection
challenges because condensed perchloric acid vapors in
improperly ventilated areas can form explosive perchlorates;
NFPA 45 provides a great deal of guidance for the design of
perchloric acid exhaust systems.
Finally, NFPA 45 provides specific guidelines for all
chemical storage, handling, and waste disposal procedures
in laboratories.
Combustible dusts
Combustible dusts are present in
a range of industries, including pharmaceuticals, chemicals and petrochemicals, grain and food processing,
and rubbers and plastics. Despite the
potential severity of explosions associated with combustible dusts, many
facilities that handle and process such
materials are unaware or ill-equipped
to deal with the associated hazards
(4–7). The remedies described in
NFPA 654, Standard for the Prevention of Fire and Dust Explosions
from the Manufacturing, Processing,
and Handling of Combustible Particulate Solids, are diverse and require
a detailed working knowledge of the
process to be protected (8).
22 www.aiche.org/cep May 2012 CEP
Explosion protection should be provided for individual
pieces of equipment, and equipment should be isolated to
prevent an explosion from propagating to other parts of a
plant. Various methods are available for either prevention
or mitigation of dust explosions within process equipment.
NFPA 654 permits the use of deflagration venting in accordance with NFPA 68, or explosion control via methods such
as deflagration suppression systems or oxidant concentration
reduction in accordance with NFPA 69 (both of which are
discussed in the next section). Deflagration venting is typically necessary for existing combustible-dust processes with
indoor dust collectors that do not have explosion protection
and that the owner does not want to relocate outdoors.
In addition to following the protection methods detailed
in NFPA 68 and 69, it is critical to limit a dust explosion
to the unit of origin. Efforts to confine an explosion to a
single process unit help to reduce the likelihood of perturbations of dust accumulations, and thus a secondary — and
usually more devastating — explosion. Several options for
isolation of process equipment are available:
• chokes. This method isolates the explosion by obstructing flow, thereby leading to the buildup of solid material.
The agglomeration of solids within a small cross-sectional
area prevents air from passing the fuel — stifling a flame
wave at the choke point. Earlier editions of NFPA 69
included screw conveyors as material chokes; however,
industry experience has shown that these devices are not
reliable as isolation devices. Rotary valves handling solid
materials can also function as material chokes.
• rotary valves. Rotary valves, which are commonly
used on equipment that handles bulk solids (e.g., silos),
restrict flow so that a vessel is open at only one end at a
time. This prevents an explosion from passing through to
Table 4. The maximum quantities of flammable and combustible liquids that can be
stored in a laboratory unit (excluding inside storage areas) are contained in NFPA 45.
Lab Unit Fire
Hazard Class
Liquid
Class
Maximum Quantities
in Use
Maximum Quantities
in Use and Storage
per 100 ft2,
gal
per Lab Unit,
gal
per 100 ft2,
gal
per Lab Unit,
gal
A
I
10
480
20
480
(High)
I, II, IIIA
20
800
40
1,600
B
I
5
300
10
480
(Moderate)
I, II, IIIA
10
400
20
800
C
I
2
150
4
300
(Low)
I, II, IIIA
4
200
8
400
D
I
1
75
2
150
(Minimal)
I, II, IIIA
1
75
2
150
The maximum quantities per 100 ft2 are used to calculate the total quantity allowed per laboratory work
area and the total quantity in the laboratory unit. They should not be interpreted as the quantity that can
be store in an area of 100 ft2.
Copyright © 2012 American Institute of Chemical Engineers (AIChE)
Product
Inlet
No
Explosion
Valve A
Rotor
Blade
Gap
Width
Electrical
Interlock
Gap
Length
Rotor
Housing
Valve B
Explosion
Rotary Valve
Product
Outlet
Process Equipment
p Figure 2. When rotary valves are used at both the inlet and outlet of a piece
of equipment, they can be electrically tied together so that only one valve can
be open at a time. This prevents explosions from traveling upstream.
the equipment upstream. Figure 2 illustrates the schematic configuration and construction of rotary valves. An
advantage of this method is that it functions as a passive
protection system.
• automatic fast-acting valve systems
• chemical isolation systems
• flame-front diverters
The last three methods use inline, automatically actuated
systems to prevent an explosion from propagating beyond
the process vessel in which it originates. Initiating the fastacting valve or chemical isolation system mechanically or
chemically interrupts the flame front, thereby preventing
the propagation of the explosion. In the case of the flamefront diverter, the deflagration must reach a preset minimum
pressure in order to rupture the valve that directs the ensuing
flame front to leave the process piping rather than continue
upstream in the process. These methods are
Extinguisher
generally easier and less expensive to retrofit into
an existing process than reconfiguring existing
process piping to avoid manifolding.
The Standard on Explosion Protection by Deflagration
Venting (NFPA 68) applies to systems that vent combustion
gases and pressures resulting from a deflagration within
an enclosure so that structural and mechanical damage
is minimized. It provides guidelines for safe deflagration
venting, including equations to determine vent size, location, and configurations that allow deflagration vents on
indoor equipment to safely vent to the building exterior.
Detailed design parameters are provided for explosion
venting where the hazard is a flammable gas or vapor or a
combustible dust.
The Standard on Explosion Prevention Systems
(NFPA 69) differs from NFPA 68 in that explosion
prevention systems address the hazard before the deflagration can progress to an explosion or limit the deflagration to a single process vessel, whereas venting systems
simply relieve the pressure generated by a deflagration.
NFPA 69 provides methods for the design and approval of
deflagration control systems.
Oxidant concentration reduction. This method reduces
or eliminates the oxidant (typically air) to prevent the formation of an explosive atmosphere within the process equipment, thus preventing a deflagration before it occurs. In a
process vessel, the air can be replaced with nitrogen, argon,
or another inerting agent, or the oxygen concentration can
be reduced to below the lower explosive limit (LEL) for the
particular material. Knowledge of the flammability characteristics of the material is needed to use this method (9).
Deflagration pressure containment. NFPA 69 allows the
use of process equipment that is of sufficiently substantial
construction to contain the overpressure associated with
a deflagration. However, this can be significantly more
expensive than the other means of dust explosion protection
discussed here, especially in existing processes.
Deflagration suppression systems. This method of
explosion protection calls for an active suppression system,
rather than one that passively vents or contains a deflagration. As shown in Figure 3, these methods discharge a sup-
Detector
Pressure
Wave
Explosion protection
NFPA defines deflagration as the propagation
of a combustion zone at a velocity that is less than
Fireball
Ignition
Explosion
Suppression
Suppression
Total
the speed of sound in the unreacted medium. A
Occurs
Detected
Begins
Continues
Suppression
detonation is a similar phenomenon that occurs at
velocities higher than the speed of sound. NFPA
Time:
30 msec
80 msec
0 msec
40 msec
20 msec
defines an explosion as the bursting or rupturing
p Figure 3. The presence of an overpressure wave triggers the discharge of the suppresof an enclosure or a container due to the develop- sant in a deflagration suppression system. The events that occur within a vessel between
ignition and full suppression can take about 80 milliseconds. Source: NFPA 654.
ment of internal pressure from a deflagration.
Copyright © 2012 American Institute of Chemical Engineers (AIChE)
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May 2012
www.aiche.org/cep
23
Safety
pressant into the protected vessel or piping when triggered
by an overpressure wave caused by deflagration.
Dilution with a noncombustible dust to render the
mixture noncombustible. In most processes, this method
is not appropriate, as dilution with a noncombustible dust
would render the combustible dust “product” unusable.
This method is also limited in effectiveness due to the high
concentrations of inert material required and the potential
for separation during handling; other methods are preferred.
This method may be appropriate for waste streams (6).
Deflagration venting through an approved dustretention and flame-arresting device. Essentially a modified version of deflagration venting, this method provides
additional protection by preventing the dust and flame
wave from passing the point of the deflagration vent. The
dust-retention and flame-arresting device must be approved
by a recognized testing laboratory.
Other codes and standards of interest
The Standard for Combustible Metals (NFPA 484)
contains several chapters detailing protection methods for
combustible metals and metal dusts, including alkali metals
(e.g., sodium, potassium), aluminum, magnesium, tantalum,
and others. Specific processes involving each of the subject
metals are discussed, including melting operations, processing and fabrication operations, and scrap storage. Protection from water and moisture is a primary consideration
when dealing with combustible metals. In some cases, fire
protection systems may consist solely of Class D manual fire
extinguishers because the application of water, even from
sprinkler systems, is deemed extremely hazardous.
The Standard for Spray Application Using Flammable
or Combustible Materials (NFPA 33) and the Standard for
Dipping, Coating, and Printing Processes Using Flammable or Combustible Liquids (NFPA 34) deal with hazards
associated with specific flammable and combustible liquid
processes. NFPA 33 focuses on spray applications such as
paint booths, while the scope of NFPA 34 is limited to dipping and coating processes. As with other NFPA standards,
Jeremy Lebowitz, P.E., works as a consultant for Rolf Jensen & Associates,
Inc., a fire-protection engineering consulting firm (Boston, MA; Phone:
(508) 620-8900; Email: jlebowitz@rjagroup.com). He has experience
designing automatic sprinkler systems and fire alarm systems, and specializes in assisting end users with fire protection requirements for the
use and storage of hazardous materials in high-hazard, chemical plant
processing and laboratory applications. He has assisted many facilities
in developing sprinkler specifications and electrical classification, and
designing ventilation, spill containment and drainage, laboratory units,
and storage facilities. In addition, he also has experience with hydrogen, compressed natural gas, and combustible dust hazard evaluation,
including the recent U.S. Occupational Safety and Health Administration (OSHA) requirements for combustible dusts. He has an MS in fire
protection engineering and a BS in chemical engineering, both from
Worcester Polytechnic Institute. He is a licensed professional engineer
in Massachusetts.
24 www.aiche.org/cep May 2012 CEP
they include information on electrical ignition sources,
and ventilation and storage methods. Static electricity is a
primary concern in such facilities. Particular care must be
exercised with drying or curing processes, since flammable
vapors and heat sources coexist in such environments.
NFPA 77, Recommended Practice on Static Electricity, is a very valuable resource for mitigating the hazard of
static electricity. NFPA 77 provides tools to assist the user in
evaluating and controlling static electricity hazards, including specific guidance for facilities handling flammable and
combustible liquids (and their vapors), powders, and dusts.
Static electricity is of particular concern where flammable
liquids are dispensed or sprayed; bonding and grounding
procedures are a primary consideration, in addition to rates
of product addition, inerting procedures, and sampling.
Final remarks
The NFPA codes and standards contain a wealth of
information based on voluminous research and more than a
century of experience with fires. Chemical engineers should
be aware of the information and recommendations available
CEP
to help create a fire-safe work environment.
Literature Cited
1. National Fire Protection Association, “National Electrical
Code,” NFPA 70, Article 500, Section 500.5, NFPA, Quincy,
MA (2011).
2. National Fire Protection Association, “Recommended
Practice for the Classification of Flammable Liquids, Gases, or
Vapors and of Hazardous (Classified) Locations for Electrical
Installations in Chemical Process Areas,” NFPA 497, NFPA,
Quincy, MA (2012).
3. van Amerom, U., “Choose the Right Electric Motors for Hazardous Locations,” Chem. Eng. Progress, 107 (11), pp. 18–23
(Nov. 2011).
4. Perry, J., et al., “Addressing Combustible Dust Hazards,”
Chem. Eng. Progress, 107 (5), pp. 36–41 (May 2011).
5. Ebadat, V., “Managing Dust Explosion Hazards,” Chem. Eng.
Progress, 105 (8), pp. 35–39 (Aug. 2009).
6. Perry, J., et al., “Conducting Process Hazard Analyses for
Dust-Handling Operations,” Chem. Eng. Progress, 105 (2),
pp. 28–35 (Feb. 2009).
7. Shelley, S., “Preventing Dust Explosions: Are You Doing
Enough?,” Chem. Eng. Progress, 104 (3), pp. 8–14 (Mar. 2008).
8. National Fire Protection Association, “Standard for the Prevention of Fire and Dust Explosions from the Manufacturing,
Processing, and Handling of Combustible Particulate Solids,”
NFPA 654, Section A.7.1.2.1(6), NFPA, Quincy, MA (2006).
9. Crowl, D., “Minimize the Risks of Flammable Materials,”
Chem. Eng. Progress, 108 (4), pp. 28–33 (Apr. 2012).
Additional Reading
Schram, P., et al., “Electrical Installations in Hazardous Locations,”
3rd ed., NFPA, Quincy, MA (2009).
Copyright © 2012 American Institute of Chemical Engineers (AIChE)