Subject: Hazardous Area Classification
E. Confined Space: An enterable space not normally occupied with limited exit and
ventilation. May or may not be a classified area depending on location, process or
atmosphere.
F. Digester Gas: Gas mixture produced by anaerobic decomposition of sludge
produced in wastewater treatment processes. Found in digesters, dewatering and
cake storage areas. Composed of 65% methane, 30% CO2, 5% other gases. LEL:
5%; UEL: 15%.
G. Division: Sub-category of hazard classification based on likelihood of hazardous
condition. Division 1 implies condition may occur in normal operation; Division 2
implies condition occurring due to accident or malfunction.
H. Explosion Proof: Electrical equipment enclosure certified to be capable of
containing an explosion of a flammable atmosphere within itself without igniting such
atmosphere outside of the enclosure.
I.
Explosive Limit (also Flammable Limit): The percentage concentration in air of a
flammable gas or vapor below which (Lower Explosive Limit, LEL) or above which
(Upper Explosive Limit, UEL) ignition will not occur.
J. Flammable Liquid: Liquid will easily ignite and burn vigorously; produces vapors
that can form an ignitable fuel-air mixture (flashpoint <100°F).
K. Flammable Gas: A material that is normally a gas at room temperature that can
form ignitable fuel-air mixtures. (i.e. digester gas).
L. Gas-Tight: Will not permit gases or vapors to pass; applies to wall penetrations and
conduit seals.
M. Hazardous: As applied herein to Area Classification, means at risk of fire or
explosion due to the nature of material and/or process. (Note that this term is
different than used in the term hazardous waste covered by other regulations.)
N. Hazardous Atmosphere: A mixture of a flammable gas or vapor and air that is
capable of being ignited by a source of ignition, e.g., a spark or electrical contact
opening.
O. Hazardous (Classified) Location: Also called Hazardous Area: a location that has
been classified based on the properties of the flammable gases, vapors or liquids
present and where risk is more likely of fire or explosion such that specific
precautions should be taken to reduce such risk (e.g., sealed pushbuttons, conduit
seals, explosion proof motors, more ventilation, etc.).
P. Hot Work: Work tasks, such as welding, grinding, cutting, etc. which generate
sparks, electric arcs, hot surfaces or open flame which could ignite a hazardous
atmosphere.
Q. Intrinsically Safe: Equipment and wiring certified to be incapable of igniting a
specific hazardous atmosphere.
R. NEC: NFPA 70, the National Electrical Code. Provides specific guidance for all
electrical installations in all locations.
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Subject: Hazardous Area Classification
S. NFPA: National Fire Protection Association: primary standards and code-making
body.
T. NFPA 820: Standard for Fire Protection in Wastewater Treatment and Collection
Facilities.
U. OSHA: Occupational Safety and Health Administration
V. Sealed: Completely barriered against entry of external atmosphere. May be factorysealed (hermetically potted) or field-installed (conduit seal fitting or wall penetration).
W. Sewer Gas: Gas mixture occurring in sewer collection systems as a by-product of
decomposition of organic matter in sewage. Composed of 70% CO2, 5% methane,
25% other gases, including H2S. LEL: 5.3%; UEL: 19.3%.
X. Unclassified: After an Area Classification has been done, this is the zone
determined to be of minimum hazard (also called “non-hazardous”) outside of a Div 2
area. (Does not imply that a classification has not been determined for a particular
area nor does it imply that there is no hazard whatsoever.).
III.
Policy Statement
A. Summary
1. There are particular locations in OCSD facilities where there is a risk of explosion
or fire due to the presence of flammable gases or vapors. These locations have
been identified in a process known as Hazardous Area Classification.
2. To minimize the risk of explosion or fire in some of these locations, additional
barriers and ventilation systems have been installed. The electrical equipment and
wiring there must meet specific electrical code requirements for hazardous areas.
3. These specialized installations must be kept in operable condition and must not be
disabled or removed.
4. Before considering the installation of equipment in any process area, the area
classification of that location should be determined by reviewing its area class map
and/or checking with the Safety and Engineering Divisions.
5. Work that may produce a spark or other source of ignition, or the opening of
enclosures with energized electrical systems in Class I, Division 1 or Class I,
Division 2 locations will require Hot Work Permits and may require specialized
tools, equipment and training.
6. OCSD is requiring any staff member who enters a waste water process area to
have on their person and use an atmospheric monitor that measures Lower
Explosive Levels (LEL) due to the numerous classified locations at OCSD facilities
and the use of electric vehicles, non-intrinsically safe equipment, or personal
electronic devices.
B. Responsibilities
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Subject: Hazardous Area Classification
1. It is the responsibility of all affected OCSD employees to become familiar with and
follow the requirements of this policy.
2. It is the responsibility of OCSD management to ensure that this policy is being
adhered to at all times.
3. It is the responsibility of the OCSD department contracting with outside workers to
ensure that the contractor’s employees are familiar with and adhere to the
requirements of this policy at all times. This especially applies to all Construction
and Maintenance Service contractors.
4. Employees are expected to have an atmospheric monitor on their person when
entering a process area that is calibrated and working properly.
5. When working with a group, at least one employee in the group shall have an
atmospheric monitor that is properly calibrated and on. The monitor can provide
coverage for a ten (10) foot radius. If the group is working over an area greater
than 10 foot then more monitors will be needed to provide coverage.
C. Regulations and Codes
Area classification is governed by Federal and State occupational safety
regulations which in turn are based on industry safety standards.
1. OSHA 29CFR 1926.407: Hazardous (Classified) Locations
a. This section is the Federal OSHA regulation regarding electrical equipment
and wiring in locations which are classified based on the properties of the
flammable material present.
2. Cal-OSHA CCR Title 8, Division 1, Chapter 4, Subchapter 5 Electrical Safety
Orders, Article 59: Hazardous (Classified) Locations.
a. This is the State of California’s law concerning area classification. The law
includes specific requirements for various industrial occupancies. A specific
section 2540.10 applies to Wastewater Wells.
3. NFPA 70, National Electrical Code (NEC) Article 500 (and following)
a. The NEC stipulates the requirements for safe installation of electrical
equipment and wiring in all locations, especially hazardous locations
b. It includes specific sections providing classifications for some commonly
encountered locations (e.g., gasoline stations) but does not otherwise
address how to classify areas in a given occupancy or industry.
4. NFPA 497, Recommended Practice for Classification of Flammable Liquids,
Gases or Vapors
a. This document provides the generic method for how to classify any area
based on the factors of material flammability, environment and overall
process. It is geared mostly to the petroleum and chemical industries.
5. NFPA 820, Standard for Fire Protection in Wastewater Treatment and Collection
Facilities,
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Subject: Hazardous Area Classification
a. This is the fire protection standard for the wastewater industry. It provides
rules and guidelines for determining the area classification of all areas of
wastewater collection and treatment facilities. It also specifies the amount of
ventilation required to reduce the classification of some areas so that
electrical installation requirements can be simplified without compromising
safety.
6. NFPA 37, Standard for Installation & Use of Stationary Combustion Engines and
Gas Turbines
a. NFPA 820 specifically excludes engine rooms and instead refers to this
standard which provides guidance for engine room area classification. .
Based on NFPA 37, Central Generation and Standby engine rooms at OCSD
are Unclassified.
D. Previous OCSD Area Class Studies and Compliance Projects
Projects have previously been undertaken to classify, assess compliance of, and
upgrade OCSD pump stations and treatment plant facilities
1. Project 2-37, Rehabilitation of Outlying Pump Stations, Final Report (Jan 1999
a. This study by MacDonald Stevens assessed and documented the compliance
to NFPA 820 of OCSD’s collection system pump stations and metering
facilities. Area class drawings were created for each facility.
b. Since this study was completed, several pump stations have been upgraded
or replaced in subsequent design and construction projects. In each case,
the design package included new area class drawings.
2. Project J-35, Hazardous Area Classification Study for Treatment Plants 1 & 2, Final
Report (July 1999).
a. This study by Brown & Caldwell assessed and documented the existing
condition of OCSD’s treatment facilities per NFPA 820 requirements.
Recommendations were made to remediate areas of both plants that were
found to be out of compliance but no corrective actions were taken in this
Study. The J-35 Area Class Maps generated in this Study documented the
existing conditions at that time; they are no longer valid since remedial
corrections have been implemented in the subsequent J-35-2 project.
3. Project J-35-2, Area Classification Implementation Plan for Plant Nos 1 & 2
(August 2006).
a. This construction project designed by Parsons and constructed by J.F.Shea
corrected many conditions found to be out of compliance with NFPA 820.
Digester gas piping was relocated out of the utility tunnels and gas-tight
barriers were installed in various locations. Additional ventilation, air
monitoring and electrical equipment were also installed. The project design
package included updated area class maps that were then finalized at the
end of construction.
E. Engineering Standards and Guidelines
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Subject: Hazardous Area Classification
The OCSD Engineering Department creates and maintains all engineering
standards and design guidelines for OCSD. Specific requirements have been
included for area classification.
1. Design Guidelines
a. Chapter 9 – Gravity Sewer & Outlying Pump Stations, Section 3.3 Hazardous
Classifications & Criteria.
1) This section provides excellent guidance for all aspects of pump station
area class requirements.
b. Chapter 10 – Electrical Design Criteria, Section 10.6.1 - Hazardous Areas
1) This section offers recommendations for minimizing the installation
complexity and cost when designing for a classified location
c. Master Specifications
1) Section 17800, Gas Monitoring Devices provides guidance on specifying
and installing Combustible Gas Monitors
F. Basic Aspects of Area Classification
1. The Overall Area Classification Process
2. Determine the hazardous characteristics of the materials involved: flammability,
density, etc.
3. Determine the degrees of hazard based on the hazard characteristics, quantities
and processes Involved (e.g., volumes, pressures, temperatures, number and
types of equipment seals, etc.).
4. Divide the process area into classified locations based on risk probabilities: these
are the Divisions.
5. Area Classification Hazard Sources
a. Sources of hazard are divided into three main Classes (categories):
1) Class I: Flammable Gases or Vapors
2) Class II: Combustible Dusts (e.g., coal dust, grain chaff, sugar)
3) Class III: Ignitable Fibers or Flyings (e.g., sawdust, cotton fibers)
b. At OCSD, the hazardous locations are due to Class I sources, that is, gases
such as sewer gas or sludge gas; or vapors such as gasoline.
6. Classification Divisions
a. The level of hazard is categorized into Divisions:
1) Division 1:
A hazardous level can exist in normal operation.
2) Division 2:
A hazardous level may exist due to an abnormal condition
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Subject: Hazardous Area Classification
3) Unclassified: A hazard does not exist except in a very unlikely
circumstance (remainder of area not covered by Division 1 or 2)
b. Note: NFPA 820 takes a conservative approach to establishing divisions
within wastewater treatment and collections systems and may establish
Division requirements exceed the above definitions.
G. Hazardous Area In Contrast to Confined Space
1. A confined space may or may not be a hazardous area. It often is a hazardous
area when flammable gases or vapors are present. Regarding wastewater
facilities, California law requires that sewer manholes and pipelines, and pump
station wet and dry wells be considered hazardous areas.
2. Conversely, some hazardous areas are not confined spaces since they are outside
and in the open.
H. Area Class Documentation
OSHA requires that the area classification of all facilities be documented and that
baseline area classification documents be kept up-to-date
1. Uniform Baseline Area Class maps have been established for all facilities and are
located on the Admin Svcs/IT SharePoint site under the FRG heading. These
maps are in the process of being updated with the latest project as-builts.
2. For facilities where recent projects have occurred which have not yet been
included in the baseline maps, those recent projects have Area Class drawings
which may be consulted for the latest information.
3. A documentation update procedure is being established to maintain the Baseline
Area Class Maps in updated condition at all times.
I.
Field Notices
1. Warning Signs
a. Signs will be posted at plant entry gates to notify personnel of classified
areas. OCSD staff shall be trained in awareness of Hazardous Areas, use of
Area Class Maps, and appropriate work procedures for those areas.
2. Safe Entry Warning Lights and Alarms
a. Clearly-worded signs shall explain the meaning of the ventilation warning
(green/red) lights the LEL warning lights and alarms, and appropriate
response to them.
J. Some Specific Hazardous Locations at OCSD Facilities
1. Sewer Lines, Manholes and Pump Stations: sewer gas; gasoline (rare)
2. Headworks and Primary Basins: sewer gas; gasoline (rare)
3. Odor Scrubbers: sewer gas; gasoline (rare)
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Subject: Hazardous Area Classification
4. Digesters and Digester Pump Rooms: digester gas
5. Gas Compressors: digester gas
K. Electrical Installation Guidelines
1. Conduit Seals
a. Seals are conduit fittings that, when properly installed, block passage of
gases inside a conduit run. The NEC prescribes where they are to be used in
classified areas. The manufacturer’s sealing compound must be poured
around the wires inside for the seal to be effective.
2. Purged Enclosures
a. Purging of control panels located in classified areas is an effective technique
to avoid having to install a massive and expensive explosion-proof enclosure
having dozens of cover bolts. Purged panels installed at OCSD use
Instrument Air as the purging gas. The purge air pressure is monitored and
will alarm if pressure is lost or the door is opened.
3. Factory Sealed Field Devices
a. The use of factory sealed pushbutton stations and selector switches reduces
the need of conduit seals. Repair of these stations requires replacement of
the entire device.
4. Explosion-Proof Motors
a. Explosion-proof motors for Division 1 locations are more expensive than Div
2 or normal motors. When choosing where to place new equipment, attempt
to stay clear of Div 1 areas so that Div 2 motors can be used instead.
5. Light Fixtures
a. Classified Area light fixtures are designed to operate with cooler surface
temperatures than normal fixtures. Replacement lamps and ballasts must
match the original equipment to keep this temperature down.
L. Ventilation Requirements
1. NFPA 820 specifies continuous ventilation requirements for each type of facility
with the potential for flammable gases and vapors at OCSD. In general, the area
classification of a space depends on how much ventilation is provided
2. Area Class Reduction by Increased Ventilation or Positive Pressurization in my
instances if increased ventilation is provided, the classification of a location may
be reduced. Critical rooms (e.g., electrical or control rooms) can be kept at a
slightly higher pressure than outside in order to ensure that no gases may enter.
The ventilation system in both cases must meet additional requirements for
reliability and monitoring.
3. Ventilation Monitoring
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Subject: Hazardous Area Classification
a. Ventilation systems for classified areas are monitored for sufficient air flow
and the detection of combustible gas or smoke; alarms are indicated locally
and at the Control Center.
M. Classification of Digester Pump Rooms at OCSD
1. Typically, Digester Pump Rooms are classified as Class I, Division 1 areas (or Div
2 with sufficient ventilation) per NFPA 820. However, project J-35-2 removed all
digester gas piping from these rooms and provided positive-pressure ventilation
with monitoring which permitted the rooms to be downgraded to Unclassified.
N. Activities in Classified Areas
1. Abatement of Hazard
a. Hazardous areas may be made safe for all activities by removing the material
hazard source. This involves complete blocking, isolation and draining or
purging of all piping and vessels (e.g., tank, digester, or basin). Then the
atmosphere must be tested in multiple locations and times, and the removal
of the source verified, to ensure that no hazard remains.
2. Requirements for Activities in Hazardous Areas
a. No vehicle parking will be permitted in hazardous areas. This includes
electric carts. See previous section “H” for locations where vehicles cannot
park.
b. Personal electronic devices are not permitted in hazardous areas. This
includes cell phones, personal digital assistants, laptops, cameras, etc. The
only exceptions to this policy are those devices specifically approved by the
OCSD Risk Management Division. All non-approved devices shall be kept
outside of the hazardous area. Powering down a device is not sufficient to
comply with this requirement.
c. In cases where use of unapproved devices is unavoidable, continuous
atmospheric monitoring for combustible gases shall be provided at the
location where the device is being used. If the monitor alarms at any time,
personnel are to cease use of the unapproved device, de-energize any
potential ignition sources, and evacuate the hazardous area until such time
that the atmosphere has been tested as clear and management approves
entry back to the work area.
3. Atmospheric Monitoring
a. The atmospheric monitors presently in use at OCSD provide measurement of
explosion hazard in terms of percentage of LEL (Lower Explosive Limit) for
hydrocarbon gases (e.g., methane). Personnel using them must be qualified
by training and certification
4. Hot Work Permits
a. Any activity in a hazardous area that could provide a source of ignition must
be reviewed and approved in a Hot Work permit process prior to the start of
such activity. Safety SOP-118 Hot Work Permit requires specific
requirements for working in Hazardous Classified Areas.
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Subject: Hazardous Area Classification
5. Non-Sparking Tools
a. Hand tools such as chisels, shovels and wrenches are available that have
been listed and certified as non-sparking for use in hazardous areas. Prior
approval by the Risk Management Division is required for the purchase and
use of these tools. Use of these tools in hazardous areas does not eliminate
the requirement for a Hot Work Permit for such activities.
O. Training
The following training course topics are pertinent to Hazardous Area Classification:
1. Hazardous Location Awareness
a. This short course is for all personnel except office staff that does not enter
process areas. The course should review the contents of this policy.
2. Working in Hazardous Locations (Hot Work)
a. This course should cover use of non-sparking tools, hot work permits, any
specialized personal protective equipment, and use of atmospheric monitors.
3. Atmospheric Monitors
a. This course is already taught in the OCSD Training curriculum.
Implementation of this policy may require additional personnel to be trained in
the use of Atmospheric Monitors.
IV.
Recordkeeping
All records created or generated in the course of this procedure shall be legible and
stored in a way that they are readily retrievable in facilities or electronic
document/content management systems that provide a suitable environment to prevent
damage, deterioration, or loss. Records may be in the form of any type of media, such
as hard copy or electronic media. The OCSD Records Retention Schedule is the official
procedure governing the retention, retirement, and destruction of District records.
Document owners should use these schedules to determine the item and series that
best fit their records. Document owners are responsible for insuring that documents are
properly marked, indexed, and filed for their projects or area of responsibility.
V.
Exceptions/Conditions/Provisions
VI.
References
A. Government Regulations:
1. OSHA 29CFR 1926.407: Hazardous (Classified) Locations
2. Cal-OSHA CCR Title 8, Division 1, Chapter 4, Subchapter 5 Electrical Safety
Orders, Article 59: Hazardous (Classified) Locations
B. National Fire Protection Association (NFPA) publications:
1. NFPA 70, National Electrical Code (NEC), latest edition
2. NFPA 497, Recommended Practice for Classification of Flammable Liquids,
Gases or Vapors
3. NFPA 820, Standard for Fire Protection in Wastewater Treatment and Collection
Facilities.
4. NFPA 37, Standard for Installation & Use of Stationary Combustion Engines and
Gas Turbines.
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Subject: Hazardous Area Classification
C. OCSD Engineering Projects
1. Project 2-37, Rehabilitation of Outlying Pump Stations, Final Report (Jan 1999.
2. Project J-35, Hazardous Area Classification Study for Treatment Plants 1 & 2, Final
Report (July 1999).
3. Project J-35-2, Area Classification Implementation Plan for Plant Nos 1 & 2
(August 2006).
4. Project J-35-2 Parsons Memo dated 3-6-2007 re: Digester Pump Room
Classification.
5. Project J-35-2 Project Decisions Log, Rev. 5 dated 7-10-2001 re: Item No. 40:
Digester Pump Rooms.
VII.
VIII.
Revision History
Version
Date
By
Reason
Attachments
Policy Number: ADM-SOP-640
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Effective Date: 3/24/2014