INTRODUCTION
A hazardous location is any location where a potential hazard, either a fire or an explosion can exist due to the presence of flammable, combustible, or ignitable materials.
These materials can consist of gases, vapors, liquids, dusts, fibers, etc.
HAZARDOUS LOCATION TYPES
Class I Locations:
An area where flammable gases or vapors are or can be present in the air in quantities sufficient to produce explosive or ignitable mixtures. For Example
* Petroleum Refineries, Gasoline storage and dispensing areas, Dry cleaning plants, Spray Finishing areas, utility gas plants.
Class II Locations:
An area where presence of combustible dust present a fire or explosion hazard. For example:
Grain elevators, flour and feed mills, Use or store of magnesium or aluminium powders, producers of plastics, fireworks.
Class III Locations:
An area made hazardous due to the presence of easily ignitable fibers or flyings. For example:
Textile mills, cotton gins, cotton seed mills, plants that shape or cut wood and create sawdust or flyings.
Hazardous Location Conditions
In addition to the types of hazardous locations, the kind of conditions under which these hazards are present are very important : Normal Conditions, Abnormal Conditions.
Division 1: Normal Conditions
Division 2 : Abnormal Conditions
Continued
Class I, Class II, and Class III hazardous locations can be either Division 1 or Division 2
Good examples of Class I, Division 1 locations: areas near open dome loading facilities or adjacent to relief valves in a petroleum refinery, because the hazardous material would be present during normal plant operations.
Continued
Closed storage drums containing flammable liquids in an inside storage room would not normally allow hazardous vapors to escape into the atmosphere but, what happens if one of the containers is leaking? You have got a Division 2 – Abnormal – condition … A Class I, Division 2 hazardous location.
Class I, Division 1 & Class I, Division 2
Class II, Division 1 & Class II, Division 2
Class III, Division 1 & Class III Division 2
Nature of Hazardous Substances
The gases and vapors of class I locations are broken into four groups : A, B, C, and D. These materials are grouped according to the ignition temperature of the substance, its explosion pressure, and other flammable characteristics.
Group A is an atmosphere containing acetylene.
Equipment with rating up to 536º F (280ºC) can be utilized.
Group B is an atmosphere containing hydrogen, or gases or vapors with a hazard equal to hydrogen. Butadiene, and ethylene and propyleneoxide are included in this group.
Group C
Group C is an atmosphere containing cyclopropane, ethyl ether, or ethylene or gases or vapors with hazard equal to these gases.
Group D is an atmosphere containing acetone, alcohol, benzine, butane, gasoline, propane, natural gases or gases with vapors with a hazard equal to these gases.
Nature of Hazardous Substances
In Class II - dust locations – we find the hazardous materials in Groups: E, F, G. These groups are classified according to the ignition temperature and the conductivity of the hazardous substance.
Conductivity is an important consideration in Class II locations, especially with metal dusts.
Group E is an atmosphere containing metalic dusts or other dusts with a similar hazard that is equivalent, such as Aluminium and Magnesium dusts.
Group F is an atmosphere containing Carbon Black, Charcoal Coal, or Coke dusts with 8% or less total volatile material.
Group G is an atmosphere containing grain dusts, flour , starch, cocoa, and similar types of materials.
Equipment for Hazardous Locations
Equipment for Class I locations:
The equipment used in Class I locations are housed in enclosures designed to contain any explosion that might occur if hazardous vapors were to enter the enclosure and ignite.
Also it is designed to cool and vent the products of this explosion.
Types of Protection
Type Letter
|
Protection Type
|
Description
|
- d
|
Flameproof enclosure
|
Withstand internal explosion of gases enter it.
|
- I
|
Intrinsically safe
|
Electrical energy restricted to a level below that which can cause ignition
|
- p
|
Pressurization/
Dilution
|
Pressurization with proactive gas
|
- e
|
Increased safety
|
Additional measures against excessive temp. and arc/sparks
|
- o
|
Oil immersion
|
Oil immersion
|
- q
|
Powder/sand fill
|
Filled with sand or powder
|
- m
|
Encapsulation
|
Encapsulation off all parts
|
International Protection (IP)
First digit of international protection marking scheme: protection against personal contact and ingress of solid objects. (6)
Second digit of (IP): protection against personal contact and ingress of water (8)
Increasing the number, the protection increased.
Equipment for Class II Locations
Class II locations make use of equipment designed to seal out dust. The enclosures are not intended to contain an internal explosion, but rather to eliminate the source of ignition so no explosion can occur within the enclosure.
Equipment for Class III Locations
Equipment used in class III locations need to be designed to prevent fibers and flyings from entering the housing. It also needs to be constructed in such a way as to prevent the escape of sparks or burning materials.
It must also operate below the point of combustion.
