Accident and Incident

"The only certainty in life is death; uncertainty lies in when and how death occurs…… Man strives to delay its onset and extend the quality of life in the interim. Threats to these objectives involve risks, some natural, some man-made, some beyond our control and some controllable".
----- William Rowe

What Is an Accident?

An unplanned, unwanted, but controllable event which disrupts the work process and causes injury to people.

Most everyone would agree that an accident is unplanned and unwanted. The idea that an accident is controllable might be a new concept.
An accident stops the normal course of events and causes property damage or personal injury, minor or serious, and occasionally results in a fatality.


By dictionary definition: “an unforeseen event”, “chance”, “unexpected happening”, formerly “Act of God”
From experience and analysis: they are “caused occurrences”
Predictable - the logical outcome of hazards
Preventable and avoidable - hazards do not have to exist. They are caused by things people do -- or fail to do.

Hazard: It is a condition with the potential of causing injury to personnel, damage to equipment or structures, loss of material, occupational illness / disease, environmental pollution / damage etc. In short, hazards are capable of producing adverse effect on Safety, Health and Environment.


RISK: It is the probability of an event-occurring and the consequences if it occurs. It may be indicated by the probability of accidents, loss of lives and the damage of any operating unit.


Incident: An event or chain of events which could have caused injury, illness and/or damage (loss) to assets, the environment or third parties.

Dangerous occurrence: A dangerous occurrence can be defined as, “any incident that has a high potential to cause death or serious injury”.

Near-miss” incident: A “near-miss” incident can be defined as, “any event, which under slightly different circumstances, may have resulted in injury or ill health of people, or damage or loss to property, plant, materials or the environment or a loss of business opportunity.

Example:A window cleaner dropping a bucket from a height, which just missed a person standing underneath, would be classed as a “near-miss” incident. This incident did not cause an injury to a person but, under slightly different circumstances (the person standing nearer to the contact point) the person may have been injured.

Accident: An unintended and unplanned occurrence involving injury / loss of human life, damage to properties, loss of productivity etc. Accident is associated with number of losses-

• Loss of human life.
• Loss of plant, machinery and other properties
• Loss of production time
• Loss of confidence due to fear psychosis and panicky
• Loss due to compensation costs
• Loss of market goodwill

Causes of Accident:

Direct cause of injury and Accident – A harmful transfer of energy that produces injury or illness

Surface causes of accident – Specific hazardous conditions or unsafe behaviors that result in an accident

Root causes of accident – Common behaviors and conditions that ultimately result in an accident

UTILITY FLOW DIAGRAMS and P&ID

The Utility Flow Diagram shall be prepared as separate drawing titledas "Utilities Flow Diagram". The distribution of utilities for plant operation shall be shown on the drawing. The utilities for plant operation are generally classified as follows where applicable:

- Boiler Section;
- Condensate Recovery;
- Boiler Feed Water;
- Cooling Water;
- Raw Water;
- Plant and Potable Water;
- Fuel Tank;
- Dry and Plant Air;
- Nitrogen;
- Inert Gas;
- Hot Oil & Cold Oil System;
- Flare and Blow-down;

Utility Flow Diagrams shall be presented in accordance with the requirements stipulated in Standard P&IDs where applicable.

Utility Flow Diagrams shall show main distribution/collection headers and finger headers with their isolating facilities and instrumentation. The branch line and subheader arrangement shall be shown as practical as possible.



Indication criteria of connection between P&IDs and UFDs is according to the following general philosophy:

a) The indication of isolation valve shall not be duplicated on P&ID and UFD.


b) Valve and instrument which will be used for the normal operation shall be indicated on P&ID, such as:

• Block valves for water cooler inlet and outlet;
• Block valves for snuffing steam of heater;
• Globe valve for steam injection control;
• Control valves for fuel control.

c) Valves which will be used only for start-up and shut-down shall be indicated on the UFD such as:

• Header isolation valve for steam purge connection;
• Isolation valve for fuel gas or fuel oil.

Utility/common facility branch line header valves at the process Unit battery limit shall be shown. The Utility Flow Diagram shall also indicate any valve in utility/common facility individual branch lines required for process and maintenance operations even if these valves may be physically located in the pipe rack or the sequence of branches may allow in the future for a single valve to serve several branch lines.


Isolation facilities shall be indicated for:

• finger areas;
• process Unit block areas;
• at position of change from pipe rack to pipe rack.

The finger area is defined as being the area that serves a particular process area which may consist of one or more process Units. In addition to the equipment that is located alongside the finger pipe rack, the finger area also includes the equipment located alongside the main pipe rack.

Utility Flow Diagram shall be arranged to cover the whole refinery/plant area and these are divided into separate sheets each with corresponding match lines. Depending on the complexity and extent of the particular utility/common facility, sheets may be combined, extended or omitted as required.



All equipment that is supplying a particular utility common facility either from the system (e.g., steam boilers) or from a process Unit (e.g., waste heat boilers) shall be shown in a "box" in geographical location. This "box" shall give relevant equipment number(s), Unit number and sheet
number of the drawing in which the equipment is detailed.

Understanding Control loop in P&ID

About Control Loop:

Modern production systems use automatic control systems where control is carried out with minimal or without human intervention. The ‘Control loops’ used in a process industry in terms of a combination of two or more instruments or control functions arranged so that signals pass from one to another for the purpose of measurement and/or control of a process variable. The goal of process control instrumentation is to measure, monitor, and or control a process.


Following three tasks is associated with a control loop.

• Measurement
• Comparison
• Adjustment

Before we proceed it’s very essential to have a basic concept on the following terms which are needed to understand a control loop in P&ID:

1. Instrument and controller symbol and identification letter.
2. Different type of function symbols and their uses.
3. Symbol of different type of line and device  associated with control loop.
4. Instrument numbering.

To read out a control loop fro a P&ID first we have to identify the following things:

• Variable/variables are to be controlled by the control loop.
• Variables need to measure for functioning the control scheme.
• Type of instrument used for measuring variable.
• Type of controller, device and function used for controlling purpose.
• Type of signal and connection used for interlinking and transmission purpose.

EXAMPLE:

In the above example the tank is filling with the pipe line above the tank and emptying through the bottom pipe line.  The level of the liquid in the tank need to control for process purpose. So the control loop is designed here just to control the tank level. The level or height of the liquid is the process variable here and the level transmitter (LT) is used to measure the process variable continuously.A level controller (LC) is used as controller and a level control valve (LV) is used to control the flow inside the bottom pipe line.

Here the control loop is working in following steps:

• First the level transmitter (LT) is measuring the level.
• The measuring value is transmitted to level controller (LC) through electrical signal.
• The controller decide what to do depending on set or desired value.
• Then the controller send required command to the level control valve (LV) through a pneumatic signal.
• Finally the control valve increase or decrease the flow as per controller signal.

Instrument Tag or Number

An Instrument number or tag has two parts which is combination of letter and number.

• Identification letter for indicating the function and purpose of use.
• An individual tag number/Loop No./serial number.

Letter is used to classify the instrument by it's function and number is used to identify the loop/interlock. Identification letters on the ISA symbols indicate:

• The variable being measured (e.g. flow, pressure, temperature).
• The device’s function (e.g., transmitter, switch, valve, sensor, indicator).
• Some modifiers (e.g., high, low, multifunction).

In the instrument tag number in above figure the initial letter indicates the measured variable. The second letter indicates a modifier, readout, or device function. The third letter usually indicates either a device function or a modifier.

In that cases where the instrument is considered to be identified by it's location/area then the instrument tag number format will be as bellow:

Connected line/link and device symbol used in control loop:

Different types of symbol are used to describe the connection/link between instrument, device, controller etc.

Following line symbol are generally used for representing a complete control loop:

Symbol of control and measuring device used in process control:

Valve and Actuator

Measuring device

Instrument symbol and Identification

Measuring Instrument Symbol:

 

 

Final Element Symbol:

 

Related Device Symbol:

 

Instrument Identification Letter:

 

Function symbols and their uses:

Shape like circles, squares, diamonds, hexagons, and lines used to represent the hardware and software instruments and functions as follows:

• Discrete Devices and Functions, represents discrete hardware instruments and functions that are implemented in non-microprocessor-based systems similar to single-case transmitters, controllers, indicators etc.

• Shared Devices and Functions, represents shared and distributed software analog instruments and functions that are implemented in microprocessor-based systems similar to distributed control or programmable logic control systems.

• Shared On–Off Devices and Functions, represents shared and distributed on–off software instruments and functions that are implemented in microprocessor-based control systems similar or equal to a distributed control or programmable logic control systems.

• Computer Devices and Functions, represents shared and distributed on–off software instruments and functions that are implemented in a computer-based control system

Line designation or line numbering

Line numbering or designation for each major line, especially header is very important to trace flow continuation for a multipage project drawing. There is several standard for such numbering system.

A line can be identified by its number, fluid to be handled, location in plant, line size, MOC etc. These parameters are the basic elements of line identity. The schematic representation of the parameters is as shown below:

Detail Description:

Line Number: Line number is a unique number assigned to every line. Every line must have a different line number i.e. the number should not be repeated for various lines.

Depending on the type of fluid the lines can be further numbered. For example lines for process fluids can have numbering in one range, say, 1 to 100, utility lines can have numbering falling in another range, say, 101 to 200 and so on.



Fluid to be carried: Process lines are meant for handling various fluids. The fluids handled can be classified as Process fluids (which further includes the raw materials, the intermediate streams and the final product ) Utilities (which includes cooling water, chilled water, steam, thermic fluids, soft water, DM water etc.). For nomenclature, each of these lines are given specific codes depending on the fluid handled
CWS may indicate cooling water supply, CWR may indicate cooling water return, DMS may indicate DM water supply and so on.



Location or Area: This parameter is included in the nomenclature so as to indicate the origin of any stream in various locations of the plant. The various sections of plants are Raw material storage, processing, Intermediate Product Storage, Final product storage, Water treatment section, utility section, waste treatment section etc.


Material of Construction: Commercial pipes are available with various materials of constructions. Most commonly used materials are CS, AISI 304, AISI 316, Copper, PVC etc.
In the nomenclature MOC can be written as it is like CS for Carbon steel, AISI 304, AISI316 etc. for various grades of Stainless Steel.
Second way can be giving code for various MOC. For example Code 1 can denote CS, Code 2 can denote AISI 304 and so on.


Line size: Although the selection of line is a job of piping engineer, the line sizing can be done by Process or Piping engineer. Commercial pipes are available either as NB (Nominal Bore ) based or OD (Outside Diameter) based depending on the material of construction.
The standard sizes on NB basis are 25, 50, 80,100,150,200 etc. The corresponding sizes on OD basis are 33.4, 60.3, 88.9, 114.3, 168.3, 219.1 etc. The same are mentioned in the nomenclature.


Phase: Materials that are handled in Process plants exist in different phases. In general the flow can classified as single phase flow, two phase flow and three phase flow. Single phase flow indicates flow of solid, liquid, gases or vapors. Two phase flow indicates combination of any two of these
solid + liquid, solid + gases, liquid + vapors etc.
Three phase flow indicated combination of any three of these.
The inclusion of this parameter in the nomenclature may be optional, but the inclusion proves to be very helpful especially when the process involves several phase flows through various lines in the plant.
The details of phase can be given by complete name of the phase like solid, liquid etc.
Letters such as S, L, G and V can be used to denote respectively solids, liquids, gas and vapors.


Insulation: Process equipment and pipes are insulated either to prevent heat loss to the surroundings or to prevent heat gain from the surroundings. Accordingly there are two types of insulations – hot and cold. Depending on the temperature inside the pipe and that of the surroundings, the nature of insulation differs.
The terms “H” and “C” can thus be used to indicate the type of insulation. The inclusion of this parameter in the nomenclature is essential because it indicates the nature of fluid in the pipe which is mainly required for personnel safety in the plant.


Other: At times it becomes necessary to provide additional details in the nomenclature. These include jacketing of pipe, pipe tracing, welding type, and special lines like IBR etc. The additional detail can be indicated as it is in the nomenclature.e


A typical line number / designation should be as follows:

6044-25-L-SW4-40S-IH

6044: Serial No/Sequence

25: Nominal diameter of the line

L: Service Code

SW4: Welding Type

40S: Material Spec

IH: Insulation Type

For numbering purpose many organizations have their own format of numbering which is prepared using standard rules for equipment and line numbering.

Every organization has their own master sheet or drawing which is prepared for the purpose of standard reference and it must include all the standard symbol, notation and format required for future drawing.


Introduction to P&ID
 

More about PFD (Process Flow Diagram)

Process Flow Diagram (PFD) is a simple form of diagram that uses symbols to identify instruments and vessels and to describe the primary flow path through a process. It illustrates the general process streams, major equipment and key control loops. They also provide detailed mass energy balance data along with major stream composition and physical properties


The process flow diagram (PFD) represents a quantum step up from the BFD in terms of the amount of information that it contains. The PFD contains the bulk of the chemical engineering data necessary for the design of a chemical process. For all of the diagrams discussed in this chapter, there are no universally accepted standards. The PFD from one company will probably contain slightly different information than the PFD for the same process from another company. Having made this point, it is fair to say that most PFDs convey very similar information.

It is clear that the PFD is a complex diagram requiring a substantial effort to prepare. It is essential that it should remain uncluttered and be easy to follow, to avoid errors in presentation and interpretation. Often PFDs are drawn on large sheets of paper, and several connected sheets may be required for a complex process. Because of the page size limitations associated with this text, complete PFDs cannot be presented here. Consequently, certain liberties have been taken in the presentation of the PFDs in this text. Specifically, certain information will be presented in accompanying tables, and only the essential process information will be included on the PFD. The resulting PFDs will retain clarity of presentation, but the reader must refer to the flow summary and equipment summary tables in order to extract all the required information about the process.


Nowadays with the advent of computers and new technology, we tend to use computerized process flow diagrams. In old computer era, we used to draw process flow diagrams with the help of supporting software manually but now we have many process simulators that automatically create process flow diagrams. We can also make use of the Computer Aided Design (CAD) technology or flow chart software to enhance our process flow diagram skills


Information Provided in a Flow Summary:

Stream Number

Temperature (°C)

Pressure (bar)

Vapor Fraction

Total Mass Flow rate (kg/h)

Total Mole Flow rate (kmol/h)

Individual Component Flow rates (kmol/h)

Optional Information>

Component Mole Fractions

Component Mass Fractions

Individual Component Flow rates (kg/h)

Volumetric Flow rates (m3/h)

Significant Physical Properties

Density

Viscosity>

Thermodynamic Data

Heat Capacity

Stream Enthalpy

Stream Name

More about P&ID

PFDs should	PFDs should not
Process Piping - major process lines Major equipment symbols, names and identification numbers Flow directions Major bypass and recirculation lines Control valves and valves that affect operation of the system Control loops that affect operation of	Pipe classes or piping line numbers Process control instrumentation (sensors and final elements) Minor bypass lines Isolation and shutoff valves Maintenance vents and drains Relief and safety valves Flanges

Introduction to P&ID

Click here for Piping and Instrumentation Diagram main article

The flow sheet or flow diagram are often used in context of engineering and design application. Although this terminology is not most accurate to describe P&IDs, it’s sufficient to describe the overall family of a process based diagram to which P&IDs belong.

We can divide the process diagram in three type or step:

BFD : The Block Flow Diagram
PFD : The Process Flow Diagram
P&ID : The Process and Instrumentation Diagram

BLOCK FLOW DIAGRAM

The beauty of a BFD is its ability to outline the complete process on little more than a single sheet. The diagram usually resemble an organized chart, containing mainly text enclosed by boxes, interconnecting lines, the process commodities they transport and flow arrows to indicate flow directions.

INFORMATION PROVIDED BY A BFD

A good BFD typically contains the following:

• Individual pieces of equipment or equipment package that are denoted by a single symbol, typically a rectangle.
• Clear label illustrating function
• Lines linking equipment or process to show flow direction.
• The order of process flow arranged and if possible with a gravity bias.
• Whenever more than one line leaves a process then the processed commodity in each line should be clearly marked

TYPICAL BFD

PROCESS FLOW DIAGRAM

Process flow diagram carry more information than the block flow diagram. They show more detail about major equipment & sub system and the flow. PFD include information of the pressure and temperature of the feed and product line to and from all major equipment. Also indicate the main header and points of all control. It’s consider as the precursor of P&IDs

Information provided by a PFD

A typical PFD shows the following items:

• Process piping
• Process flow direction
• Major bypass and recirculation lines.
• Major equipment represented by simplified symbols.
• Control and process critical valves
• System ratings and operational values.
• Composition of fluids
• Connection between systems.

TYPICAL PFD

PROCESS AND INSTRUMENTATION DIAGRAM

The Piping and Instrumentation Diagram (P&ID), based on the Process Flow Diagram (PFD), represents the technical realization of a process by means of graphical symbols for equipment and piping together with graphical symbols for process measurement and control functions.

A P&ID carries a wealth of information that span engineering disciplines to define a process. The representation and designation of all the equipment, instrumentation and piping should comply with the requirements of Standard. Auxiliary systems may be represented by rectangular boxes with reference to the separate diagrams

For processing facilities, it is a pictorial representation of:

Ø Key piping and instrument details

Ø Control and shutdown schemes

Ø Safety and regulatory requirements and

Ø Basic start up and operational information

INFORMATION PROVIDED BY P&ID:

• Permanent start-up and flush lines.
• Flow directions and Interconnections references.
• Control inputs and outputs, interlocks and Computer control system input.
• Interfaces for class changes.
• Identification of components and subsystems delivered by others.
• Instrumentation and designations.
• Mechanical equipment with names and numbers.
• All valves and their identifications.
• Process piping, sizes and identification
• Miscellaneous - vents, drains, special fittings, sampling lines,reducers, increasers and swagers.

TYPICAL P&ID

More about PFD
More about P&ID 

PIPING DAIGRAM SYMBOL

Symbol is the basic notation to describe or represent a P&ID. To read and interpret piping and instrument drawing , the reader must learn the meaning of the symbol. We will discuss about the common symbols that are used to depict fluid process plant.

In general all the symbols used in P&ID are as per ISA or ANSI standard. But any organization may have their own standard which is derived from international standard.

LINE SYMBOL

COMPRESSOR SYMBOL

FUNCTION SYMBOLS

FUNCTION SYMBOLS

PUMP SYMBOLS

STORAGE SYMBOL

FITTINGS SYMBOL

EXCHANGER SYMBOL

Piping Symbols used in P&ID

Symbols for several types of valve generally used in process plant:

____________________________________________________________________

Notation used to describe a valve's position(Open/Closed/Partially open etc):

____________________________________________________________________

Symbol and abbreviation used for identifying types of instruments and their function:

____________________________________________________________________

Miscellaneous symbol used to mention direction and continuity:

P&ID ABBREVIATION AND IDENTIFICATION

Abbreviation is used to define:

1. An equipment to specify its type or service.
• Example: For a Pump generally ’AP’ abbreviation is used for numbering. AP1002, AP6009 etc.
• Example: For a Vacuum Pump generally ’AV’ abbreviation is used for numbering. AV1012, AP4007 etc.
• Example: For a storage tank 'ST' and for vessel 'AB' is used for numbering.
2. A pipe line to specify its service.
   
• Example: ‘CWR’ is used for the Cooling Water Supply line.
• Example: ‘HOS’ used for Hot Oil Supply line.
3. An Instrument to define its function.
   
• Example: ‘PRV’ used for control valve to Control Pressure.
• Example: ‘FIC’ used for Instrument which is used to Indicate and Control Flow.

Bellow is list of some abbreviation generally used in a standard P&ID:

DRAIN/SEWER ABBREVIATION



MISCELLANEOUS ABBREVIATION



ABBREVIATION FOR UTILITY SERVICE



ABBREVIATION FOR UTILITY SERVICE




INSTRUMENT ABBREVIATION

Know P&ID

More about P&ID

A P&ID sheet can be divided in following parts:

• Title Block (1st block, 2nd block, 3rd block & other information as scale, soft copy reference etc.)
  
  
• Grid System
  
  
• Revision Block
  
  
• Notes and Legend
  
  
• Equipment Specification
  
  
• Drawing (Graphic Portion)
  
  

TITLE BLOCK:

Generally title block consist 3 Area: 1st area contains drawing title, number, location or area, site and vendor. 2nd area contains signature, information of drafting, verification, approval and control. 3rd area is reference area which contains reference block and drawing information.

DIFFERENT AREA OF A TITLE BLOCK SHOWN BELLOW:



BELLOW IS AN EXAMPLE OF A TYPICAL TITLE BLOCK:



GRID SYSTEM:


Because of drawing tend to be large & complex it quite difficult to find a specific point in a sheet. This is especially true when a wire or pipe is continued on a second drawing. To locate the point in reference print most drawing has 2D coordinate grid system. The grid consist letter, number or both that run horizontally and vertically around the drawing.

TYPICAL GRID USED IN P&ID:



REVISION BLOCK:

If any change is done in a system or equipment or specification in drawings the drawing must be redrafted and reissued with a new version of the original drawing.The revision details must be mentioned in Revision Block. The original drawing must be of version 0.



NOTES AND LEGEND:

Because of the importance of understanding all the symbol & convention used in a drawing the notes and legend section must be review before reading a drawing.The legend and note section of a drawing list & explain any special symbol & convention used on the drawing. Any notes required for understanding a drawing can be mentioned here.




EQUIPMENT SPECIFICATION:

In this section the specification of essential equipment can be mentioned.

• A vessel/ tank can be specified with capacity, MOC, Empty weight, jacketing detail, tubing detail etc.
  
  
• A pump can specified with it’s disch. capacity, head, RPM, drive type etc.
  
  
• A motor can be specified with it’s RPM, rating current, voltage, frequency etc.
  
  

DRAWING:

Drawing area is the graphics section where the pictorial view of system/project/equipment is described graphically using standard symbol & procedure.

EXAMPLE OF A STANDARD DRAWING SHEET:




Generally any organization customizes and makes their own standard focusing on ISA standard.