Hazardous area classification question

Status
Not open for further replies.
Friends: I design natural gas compression stations from time to time. A question has come up about the application of certain devices. Per 500, 501 of the Code, I have always classified things that always flow gas to the atmosphere like GC instrument vents, blowdown valve vents, etc, as Class 1, Division 1, since gas is present in normal operations. But when it comes to popoff-type relief vents that only open in abnormal conditions, I have classified those areas as Division 2. Is this correct? The relief vents only open when something goes out of bounds, so I would define that as an "abnormal" condition, therefore, Division 2. Is this correct? I would like to have your thoughts on this matter. Thanks in advance for your help. Phillip Pulliam, Lexington, Kentucky.
 

Rockyd

Senior Member
Location
Nevada
Occupation
Retired after 40 years as an electrician.
Calling RB Alex.

I'm not an engineer (Alex is), but tend to agree with your assessment as the class1-div1, is gas normally present, whereas class1-div2 is not normally a occupied by the hazard. Takes a lot of the cost out considering seal-tight vs explo$ion-proof flex, etc.
 

KentAT

Senior Member
Location
Northeastern PA
I second the anticipation for Bob Alexander's reply. ;)

First off, I do not design or engineer the natural gas compressor station that I work at. But I can relate to you that every relief valve that relieves natural gas has a Div 1 area classification centered at the opening of the vent piping at my plant.

Sometimes I read that engineers believed that even though the cause of the operation of the relief valve is an abnormal event, the fact that the valve operates as designed leads some to consider this as a normal operation for the relief valve itself. I don't believe this idea carried much weight when our areas were classified as they were.

But more often explanations that are discussed are:

(1) the NEC does have a section (NEC 500.5(B)(1)) covering possible "leakage" as a criteria for requiring a Div 1 classification after weighing the frequency of such a condition. The general consensus is that a relief valve falls under this consideration, since not all valves remain bubble tight at all times. As far as the frequency goes, how can anyone detect, confirm, or place a label on the frequency of leakage that a relief valve experiences over time, barring the installation of gas detection equipment in the vent piping? After all, most vent piping openings are higher than the eaves of attached buildings.

(2) Does having a Div 1 area immediately around the vent opening cause that much of a headache anyway? Using the 5' radius for the Div 1 sphere as recommended in API-RP500 along with the additional Div 2 sphere up to 25', it shouldn't be difficult to design the contents of the area using only the equipment that is absolutely required to be in that area, thus keeping costs down.

This is just what I see happen around here - not saying it is the absolute correct answer.

Kent
 

DownRiverGUy

Member
Location
Canton, MI
I've been working on a design for a Class 1 Div 2 location and this is my 2cents...

A class 1 div 2 is considered an area where the substance in question (that gives it the class 1 rating in the first place) should NOT normally be.

Class 1 Div 1 areas are built to always have the substance in question in the area.

This is why when you see C1D1 fixture they are 100% sealed and are explosion proof while C1D2 fixtures are more robust but not the monsters that their C1D1 cousins are.

I will have to check NFPA tomorrow and see what I can find.

In my opinion your install is fine as a C1D2. But I need to double check
 
C1D1 or 2?

C1D1 or 2?

I really appreciate your help in this matter. We are building an electrical engineering department here at this company and need consensus on this matter. Please continue to give your thoughts. They are valued.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
One of the most frustrating issues in electrical area classification is determining what normal means as it relates to Arts 500 ? 516. It?s not listed in the NFPA Official Definitions nor is it in NEC Article 100 or Section 500.2. In fact, both the General and NEC specific Manual(s) of Style say it is a possibly vague or unenforceable term that ??shall be reviewed in context, and if the resulting requirement is unenforceable or vague, they shall not be used within the body of codes or standards.?

OK, so how do you know it?s enforceable and clear if it isn?t defined? NFPA provides an answer!!! Simply use Webster?s Collegiate Dictionary, 11th edition,as the source for the ordinarily accepted meaning. In this case, Webster?s Collegiate Dictionary, 11th edition only muddies the water further:
Main Entry:1nor?mal
1: perpendicular ; especially : perpendicular to a tangent at a point of tangency
2 a: according with, constituting, or not deviating from a norm, rule, or principle
b: conforming to a type, standard, or regular pattern
3: occurring naturally <normal immunity>
4 a: of, relating to, or characterized by average intelligence or development
b: free from mental disorder : sane
5 a of a solution : having a concentration of one gram equivalent of solute per liter
b: containing neither basic hydroxyl nor acid hydrogen <normal silver phosphate>
c: not associated <normal molecules>
d: having a straight-chain structure <normal butyl alcohol>
6 of a subgroup: having the property that every coset produced by operating on the left by a given element is equal to the coset produced by operating on the right by the same element
7: relating to, involving, or being a normal curve or normal distribution <normal approximation to the binomial distribution>
8 of a matrix: having the property of commutativity under multiplication by the transpose of the matrix each of whose elements is a conjugate complex number with respect to the corresponding element of the given matrix

Which one of the above do we use in Arts 500-516? If we try to force fit it into 2a or 2b we just push the problem back to determining what norm, rule, principle, type, standard, or regular pattern we must use.

Dump on top of all that things like 500.8(B)(5): Unless otherwise specified, normal operating conditions for motors shall be assumed to be rated full-load steady conditions.

So a running motor is fine but starting it isn?t ?normal? unless otherwise specified. I guarantee it isn?t ?otherwise specified? anywhere in Arts 500-516.

Alright let?s jump on standard from 2b.
OK what standard?
Why, API RP 500 or NFPA 497, of course.
But they aren?t Standards.
Huh?
They?re Recommended Practices.
Well, we?ll us?em anyway.
Fine, but they both say:
However, ?normal? does not necessarily mean the situation that prevails when everything is working properly. [API RP 500 - 6.2.2.1] or [NFPA 497 ? 5.2.1.2]
The bottom line is that, outside the scopes of Arts 511-516, electrical area classification is ultimately a judgment call and should be done by someone who knows what they are doing. Although it wounds my professional pride, the truth is, many of these details can be handled by workers experienced with ?the system,? who know ?this works? and ?that doesn?t.? Both API RP 500 and NFPA 497 recognize this.

From NFPA 497:
5.8.2.2 Existing Facility History. For an existing facility, the individual plant experience is extremely important in classifying areas within the plant. Both operation and maintenance personnel in the actual plant should be asked the following questions:
?
The ?experience? concept is woven throughout API RP 500, but it?s tougher to find it as a single statement

Occasionally, someone else needs to review it. It is rarely the local inspecting AHJ. The insurance carrier is usually better ? and of course, within the NFPA Official Definitions the insurance carrier is also an AHJ.
 

DownRiverGUy

Member
Location
Canton, MI
Per NFPA 500

(1) Class I, Division 1. A Class I, Division 1 location is a location

(1) In which ignitible concentrations of flammable gases, flammable liquid?produced vapors, or combustible liquid?produced vapors can exist under normal operating conditions, or

(2) In which ignitible concentrations of such flammable gases, flammable liquid?produced vapors, or combustible liquids above their flash points may exist frequently because of repair or maintenance operations or because of leakage, or

(3) In which breakdown or faulty operation of equipment or processes might release ignitible concentrations of flammable gases, flammable liquid?produced vapors, or combustible liquid?produced vapors and might also cause simultaneous failure of electrical equipment in such a way as to directly cause the electrical equipment to become a source of ignition.

FPN No. 1: This classification usually includes the following locations:

(1) Where volatile flammable liquids or liquefied flammable gases are transferred from one container to another

(2) Interiors of spray booths and areas in the vicinity of spraying and painting operations where volatile flammable solvents are used

(3) Locations containing open tanks or vats of volatile flammable liquids

(4) Drying rooms or compartments for the evaporation of flammable solvents

(5) Locations containing fat- and oil-extraction equipment using volatile flammable solvents

(6) Portions of cleaning and dyeing plants where flammable liquids are used

(7) Gas generator rooms and other portions of gas manufacturing plants where flammable gas may escape

(8) Inadequately ventilated pump rooms for flammable gas or for volatile flammable liquids

(9) The interiors of refrigerators and freezers in which volatile flammable materials are stored in open, lightly stoppered, or easily ruptured containers

(10) All other locations where ignitible concentrations of flammable vapors or gases are likely to occur in the course of normal operations

FPN No. 2: In some Division 1 locations, ignitible concentrations of flammable gases or vapors may be present continuously or for long periods of time. Examples include the following:

(1) The inside of inadequately vented enclosures containing instruments normally venting flammable gases or vapors to the interior of the enclosure

(2) The inside of vented tanks containing volatile flammable liquids

(3) The area between the inner and outer roof sections of a floating roof tank containing volatile flammable fluids

(4) Inadequately ventilated areas within spraying or coating operations using volatile flammable fluids

(5) The interior of an exhaust duct that is used to vent ignitible concentrations of gases or vapors

Experience has demonstrated the prudence of avoiding the installation of instrumentation or other electrical equipment in these particular areas altogether or where it cannot be avoided because it is essential to the process and other locations are not feasible [see 500.5(A), FPN] using electrical equipment or instrumentation approved for the specific application or consisting of intrinsically safe systems as described in Article 504.

(2) Class I, Division 2. A Class I, Division 2 location is a location

(1) In which volatile flammable gases, flammable liquid?produced vapors, or combustible liquid?produced vapors are handled, processed, or used, but in which the liquids, vapors, or gases will normally be confined within closed containers or closed systems from which they can escape only in case of accidental rupture or breakdown of such containers or systems or in case of abnormal operation of equipment, or

(2) In which ignitible concentrations of flammable gases, flammable liquid?produced vapors, or combustible liquid?produced vapors are normally prevented by positive mechanical ventilation and which might become hazardous through failure or abnormal operation of the ventilating equipment, or
(3) That is adjacent to a Class I, Division 1 location, and to which ignitible concentrations of flammable gases, flammable liquid?produced vapors, or combustible liquid?produced vapors above their flash points might occasionally be communicated unless such communication is prevented by adequate positive-pressure ventilation from a source of clean air and effective safeguards against ventilation failure are provided.

FPN No. 1: This classification usually includes locations where volatile flammable liquids or flammable gases or vapors are used but that, in the judgment of the authority having jurisdiction, would become hazardous only in case of an accident or of some unusual operating condition. The quantity of flammable material that might escape in case of accident, the adequacy of ventilating equipment, the total area involved, and the record of the industry or business with respect to explosions or fires are all factors that merit consideration in determining the classification and extent of each location.

FPN No. 2: Piping without valves, checks, meters, and similar devices would not ordinarily introduce a hazardous condition even though used for flammable liquids or gases. Depending on factors such as the quantity and size of the containers and ventilation, locations used for the storage of flammable liquids or liquefied or compressed gases in sealed containers may be considered either hazardous (classified) or unclassified locations. See NFPA 30-2008, Flammable and Combustible Liquids Code, and NFPA 58-2008, Liquefied Petroleum Gas Code.



It seems to me that you have a Class 1 Div 2 location there per NFPA.

Thoughts?
 

UofL07

Member
While their are many others on here that can better speak to the code implications, I have done work with a plant that classifies the area around emergency relief valves (ie opens under emergency or "non-normal" conditions) as C1D1. Their reasoning was based on it was within the normal operation on the relief valve to open and have ignitable mixtures of gas in the air. I was never quite sure why they didn't take the whole process into account but was not concerned since they erred on the side of caution. I would appreciate any thoughts on this interpretation.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
(1) In which volatile flammable gases, flammable liquid?produced vapors, or combustible liquid?produced vapors are handled, processed, or used, but in which the liquids, vapors, or gases will normally be confined within closed containers or closed systems from which they can escape only in case of accidental rupture or breakdown of such containers or systems or in case of abnormal operation of equipment
Its not a rupture or breakdown.

And its not an abnormal operation of equipment when the relief valve opens because that is what it is supposed to do.
 

rcwilson

Senior Member
Location
Redmond, WA
All gas vents and relief valve vents should be Class 1 Div 1 for 5' around the discharge. All such vents should be routed to a "safe" location. That is usually outside, high in the air.

As stated before, classifying the relief valve discharge as Div 1 seldom impacts any electrical equipment. The valve itself is not classified; just the vent where any gas is discharged.

My 35 years experience in petrochemical refineries, natural gas compressor stations and natural gas power plants is that the relief vents are always Class 1, Division 1 hazards.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
I'm fairly familiar with the NEC "Division" definitions.

Again, the problem with the NEC definitions is that normal and normally are not defined the context of the statement other than colloquially; i.e., we all just kinda understand what it means.

Bob (petersonra) mentioned certain timeframes. While it isn?t absolutely true, it is definitely a common evaluation method in IEC/CENELEC classification based practices. (Time to hawk my paper again ? it?s a bit out of date, the ATEX directive had just been published, but it?s accurate for this discussion)

A couple of IEC/CENELEC area classification advantages over either US Divisions or Zones are:

? IEC defines normal: ?The situation when the equipment is operating within its design parameters.? [IEC 79-10 Section 2.8] and then adds two examples:

1. Minor releases of flammable material may be part of normal operation. For. Example, releases from seals which rely on wetting by the fluid which is being pumped are considered to be minor releases.
2. Failures (such as the breakdown of pump seals, flanges gaskets or spillages caused by accidents) which involve urgent repair or shut-down are not considered to be part of normal operation.
? IEC Zones are defined in terms of ?probability;? Both US Divisions and Zones are defined in terms of ?possibility.?

I won?t repeat it here see my discussion Definitions?Possible Versus Probable on page 4 of the paper.

If you still don?t see the significance, the other side?s litigation attorney will gladly explain it to the jury.

Personally, I believe the OP's analysis is sound; however, Bob's (petersonra) point is well taken and sound judgment need to be applied to the likelyhood of venting.
 
Its not a rupture or breakdown.

And its not an abnormal operation of equipment when the relief valve opens because that is what it is supposed to do.

I agree; the immediate area of a releif valve exhaust should always be Division 1.

A seal leaks due to lack of maintenance, a flange breaks because of catastrophic failure. The prior gets attended eventually if it is a small leak and presents intermittent fluctuation of concentration and dispersion, going in and out of normal and >LEL range. The later is a catstrophic even that results in immediate stoppage of the process, a short duration of >LEL, then repair. During startups and upset conditions a releief valve mey keep poping off every 10 minutes for days until the process swing is stopped and corrected.
 
Last edited:
Status
Not open for further replies.
Top