Safety & Safety Management

Safety and Safety Management MSc Applied Instrumentation &Control

Contents
Coursework 1
1. Introduction
1.1.The Process
1.2. Explosive atmosphere
1.3. Zones
1.4. Equipments
2.Risk Assessment
2.1.Identify People at Risk

2.2. Hazard associated with plan area

2.3. Risk evaluation and severity

2.4. Control Measures

2.5. Actions

3.Legislations

Coursework 2
1.Introduction

2.Instrumentation System in Safety respect

2.1.Instrumentation System Design

3. Control System recommendations
4.Proposed Instrumentation system Architecture

5.Legislation in selecting Equipments

References

School of Engineering, Science & Design ,Glasgow Caledonian University
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Coursework 1:Risk Assessment for Fire and Explosion Hazards and
associated Legislations
This report firstly describes the risks for fire and explosion hazards in a pneumatic
conveying system of a pharmaceutical powder called Pharmex.Secondly ,it outlines the
related legislation for the given process.

Figure 1: Schematic diagram of the Pneumatic conveying system.

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1. Introduction
The purpose of this risk assessment is to identify and evaluate the fir & explosion
hazards before the operation of the process. Control Of Substances Hazardous to
Health (COSHH) regulations is a useful tool for this work. The motivation for this
assessment arises from the fact that the employees should be prevented from exposure
to hazards. Indeed, the implementation of COSHH regulations leads to
i) higher productivity as a result of using more effective controls, ii) improved
employee morale.
Actually in the risk assessment of fir and explosion we will try to find out where there
is enough powder that would give us explosion.Whenever powder in the air that’s fine
but if the powder is more than 80 gm/m³ it’s quite enough to have explosion.
Primarily we are interesting in preventing explosion we could have fire too sometimes
but the biggest danger this plant is that the plant move powder from one area to another
area by blowing the powder that means the pipeline has the mixture of powder and air
and got the potential of explosion

1.1 The process
In this pneumatic conveying system a pipeline is used to transfer pharmaceutical
powder called Pharmex from a blow tank to receiver vessel to some distant area.. The
powder would initially be loaded manually into the blow tank. A filter is used at the
receiver tank and finally the powder will settle down. The air compressor feeds the
system with air under a desired pressure. In figure 1, the relief valves and the regulator
valves are shown as PRF and NB respectively.

1.2.Explosive Atmospheres:
In pneumatic conveying system workplace air and pharmex can form the explosive
atmospheres and classified as hazardous area according to DSEAR [1]..Hence special
precautions over ignition and fuel sources are needed to prevent fire and
explosions.Non hazardous area i.e.,outside the workplace needs risk assessment as
well.Hazardous areas are further classified as Zones which are included in
DSEAR.When we talk about dangerous substance and explosive atmosphere
regulations then we look at Zone .Zones are important in that legislation.

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1.3. Zones
In this workplace a mixture with air and pharmex occurs. Pharmex is a substance
dangerous for explosion. The mist of air and pharmex is present continuously in very
small concentrations and occasionally in higher ones. Therefore, the place is
considered as Zone 20, according to DSEAR [1].
To start the process we have to put the powder into the plant and the powder is not
present continuously hence the filling of powder is in Zone 21 according to DSEAR.

1.4. Equipment
The proposed equipment for zone 20, is category 1 equipment, following DSEAR [1].

2. Risk Assessment
Firstly the hazards potential to harm are identified. Secondly, the risks present to
people’s health are assessed.

Regarding the conveying system shown in figure 1, the main hazards are fire and
explosion. However the crucial points for a fire or an explosion are mentioned in
paragraph.

Fire and explosion

Ignition Source

Fuel Oxidiser
Figure 2: The fire triangular

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The above triangle illustrates the rule that in order to ignite and burn, a fire, or an
explosion, requires the three elements, each one put at the edge of the triangle.
1) Ignition source: The ignition source can be directly associated to heat.
2) Fuel: Is necessary for the fire or explosion to burn.
3) Oxidiser: Substances also necessary for the reaction of fire or explosion. Oxygen is
the most usual oxidiser.
Depending on the explosibility properties of the substances where an explosive
atmosphere can form, any ignition will cause an explosion or a fire.
In the light of fire triangle it can be seen that the fuel (Pharmex) and oxidation (air) are
present in most conditions in the plant.Hence the basis of safety will be
1- The removal of ignition source
2- Minimization of risk if there is an explosion or fire.

The explosibility properties vary for different substances. Most important are:
• Minimum ignition energy gives information on the spark energy needed to
ignite a powder cloud. Whilst most flammable liquids have values of less
than two mL and hence can be ignited by almost any spark the energy
required igniting, different powder clouds can take a range of values.
• Maximum explosion pressure and maximum rate of pressure rise give an
indication about the severity odf the explosion it may happen.
• Minimum exposible concentration is a range of concentrations where the
powder cloud will not ignite even when an ignition source is available.
In the case under surveillance, the pharmaceutical powder is pharmex and the
explosibility properties are illustrated in the following table.

Minimum Maximum Maximum Minimum
ignition Explosion Pressure rise explosible
energy/mJ Pressure/ bar a Bar m/sec concentration
g/ m 3
Pharmex 15 10 156 80
Table :Characterstics of Pharmex powder
Kst (156 bar m/sec) indicates that the powder is moderately explosible.It means that
explosion would have significant risks associated with it.Also since the maximum

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explosion pressure value is above the normal range i.e., 10bar g which could be
dangerous.Also minimum ignition energy is very low 15 mJ which can be generated
easily for example by static personnel.The minimum explosible concentration 80
gm/m³ is in normal range which is not easily achieve.
2.1.Identify people at risk:
All the employees working in the plant premises and the public close to the
workplace.All visitors and contractors and maintenance staff visit the premises to carry
out routine inspection and maintenance.

2.2. Hazards associated with Plant components:
These are the hazards associated with the plant or equipment.For fire or explosion this
case requires fuel,an oxidant and an ignition source.Also hazards are related to the
inadequate,makeshift or temporary plant and equipment.

The major fire and explosion hazards related to pneumatic conveying system are

1. Blow Tank:A possible spark at the input/output of the blow tank could cause a
fire in the pipeline. The blow tank is capable of sustaining an explosion since
its should be rated at 20 barg since the MEP is 10barg.
2. The Pipe Line:The moving powder will not ignite as there will be insufficient
time for a spark to transfer energy to the moving powder. Moreover the powder
will be earthed by the pipeline.
3. Filter Housing and Receiving vessel:
This can be consider as one unit or vessel.Since it is not capable to withstand
the explosion as it’s rated pressure is 0.3 barg hence a suppression system
will be used to protect this unit in the event of an explosion.
4. Compressor: An isolation valve is needed to stop blow back to the
compressore in the event of an explosion.

Ignition Sources:
For fire and explosion hazards as we know that Pharmex is a fuel and oxidants are
always present hence there will be an fire or explosion hazard whenever there is

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ignition source present.Ignition sources can be electrical,mechanical,thermal or
chemical.

1. Static Ignition sources: Since Pharmex has the low minimum ignition energy
i.e.,15mJ hence care must be taken as there is a potential for ignition by static
generated by personnel.To overcome this earthing the plant is require and
conductive shoes should be wear.
2. Mechanical Ignition source:Tramp metal in the powder can act as an isolated
conductor and become charged and provide ignition source to the powder and it
also can provide the frictional heating source to ignite the powder.The best
thing to deal with is to filter the powder.Put the powder through the filter then
if there is a metal then we will trap it.If the metal particles small enough to go
through the filter then it wouldn’t have enough capacity for storing
charge.Valves can overheat.
3. Electrical sources of ignition:Electrical equipments may provide the ignition
source by way of spark or hot surface for example incinerators , welding, flame
cutting,heatres and heating appliances.
4. Also we have to check that are other heat sources such as light bulbs or lamps situated
close to combustible materials
5. Smoking,smoking materials, candles or other naked flame sources used in the premises
could be the source of ignition.
6. Fork Lift could be the source of ignition.

Some other Hazard sources
1. Compressed air cylinders or diesel used in generator could be the source of
oxidants. Moreover any flammables such as white spirit, turpentine, adhesives,
disposable cigarette lighters, chemical cleaners, plastics, etc. stored or used on the
premises may be source of fuel.
2. Pressure valves might not work properly.
3. Combustible materials such as clothing, paper, plastics, textiles, foam materials,
upholstered furniture or other soft furnishing materials stored or used in the premises.
2.3. Risks Evaluation and Severity:

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An indication showing that the risk is related to the exposure is given by the next
formula:
Risk = Hazard x Exposure
Once the hazards are spotted, the maximum harm possible from the hazard and the
likelihood of that harm are evaluated. These two factors produce an estimation of risk
as shown in table.
Slightly harmful Harmful Extremely
harmful
Highly unlikely Trivial Risk Tolerable Risk Moderate Risk
Unlikely Tolerable Risk Moderate Risk Substantial Risk
Likely Moderate Risk Substantial Risk Intolerable Risk
Table 1: simple risk-level estimator

Three categories of harm are used in BS 8800:

• Slight Harm: Harm that is of a temporary nature, e.g. headache or muscle strain
that dissipates.
• Harmful: Results in permanent minor disability, e.g. slight deafness, small
reductions in lung function, minor back problems.
• Extreme harm Premature death or permanent major disability.

Three categories of likelihood that harm will occur are used in BS 8800:

• Highly unlikely
• Unlikely
• Likely

The risk level associated with some hazards are pointed out in the following table.

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Hazard Risk and people Control Actions
affected
1)Severity
2)Likelihood
3)Overall risk
Fire and
Explosion(The
hazard
categories
indicate the
ignition
source and
fuel present
Spark in blow 1)Harmful -All parts of the pneumatic
tank 2)Highly unlikely conveying system should
3)Tolerable risk be earthed.
Static Charge 1)Extremely 1-Complete earthing of the Regular
Harmful equipments. testing.
2)Likely 2-The personnel should
3)Intolerable risk wear conductive shoes

Electrical 1)Extremely -Equipment should be of Periodic
Appliances Harmful correct rating . electrical
and fixtures 2)Unlikely -Periodic maintenance of tests on the
- 3)Substantial risk the equipment to ensure equipments
that there are no should be
insulations defect or carried out.
heating possibilities.
-All electrical equipments
must to undergo portable
appliance testing
equipment each year.
-Clear instructions
displayed as to the nature

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of the electrical hazards
Elecrocution 1)Extremely The room must be securely
during Harmful locked out of service while
maintenance 2)highly unlikely maintenance is being
3)Moderate risk carried out.Maintenance
must be carried out by
competent staff.
Hot works 1)Extremely Competent person review Hot work
And heating Harmful and assess any hot works. permit system
2)Highly unlikely should be
3) Moderate risk considered.
Smoking & 1)Extremely A safety policy should Regular audit
smoking Harmful include No smoking. No smoking
material 2)Unlikely sign must be
3)Substantial Risk present at the
entry door
Compressed 1)Extremely -There must be no leakage Move the air
air cylinders Harmful in the air cylinders. compressor to
2)Highly unlikely - Periodic maintenance on a separate
3)Moderate risk the cylinders should be room
carried out.
Diesel 1)Extremely -There must be no leakage Move the
Generator Harmful in the diesel generator.. Diesel
2)Highly unlikely - Periodic maintenance on Generator to
3)Moderate risk the generator should be a separate
carried out. room
Table 2: Hazards,Risk Evaluation ,Controls and actions

2.4. Controls
Each risk level is related to different controls given in the following table.

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Risk level Action and time scale
Trivial no action nor documentary records
needed - but good practice to record the
assessment
Tolerable improvement not mandatory, but record
and monitoring required to ensure
controls are maintained. Go for cheap
improvements where possible
Moderate Aim to reduce risk but costs of
prevention may be limited. Measures
should be tied to a timetable
Substantial Work should be avoided in the presence
of risk and if started then urgent actions
should be taken to reduce it.
Intolerable Better not to start the work before
reducing the risk and if it is not possible
to reduce the risk then work must
remain prohibited.
Table 3: Risk-Control relationship

If a substance has Maximum Exposure Limit (MEL) it will require monitoring unless it
can be shown that there is no significant risk of the substance exceeding the MEL in
the operation concerned. The same happens when the substance has Occupational
Exposure Standards (EOS).

The fire or explosion is controlled or extinguished by removing any of the elements of
the fire’s triangle. In the main parts of the plant there is always enough concentration
of powder that could explode..Now what we have to do is to make sure that no ignition
sources should be present inside the plant.The best way to deal with this is that all the
plant is earthed .It means that that any static charges on the plant go to earth and don’t
accumulate and it also means that any bits of the plant that are not connected by metal
tube would need earthed as well.The whole plant has to be bounded to earth.The
powder will also be earthed by contacting with the pipeline if it may become charge.
For the given hazards the suggested controls are mentioned in table 2 risk evaluation
and control.Moreover some other controls which helps in reducing the risks are

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1. The personnel should wear conductive shoes, earthing.
2. Maintain the valves.
3. Often checks and measurements.
4. Monitoring flow.
5. Monitoring temperature.
6. Monitoring pressure.
7. Evaluate the case of possible spark.
8. Screen the material prior to conveying.

2.5.Actions
To reduce the risk of fire and explosion the actions described in the table 2 should be
taken. Moreover the following actions [6] will also help in reducing and controlling
risks of fire and explosion hazards.

1 The Plant area is restricted to the trained staff only.
2 The storage and use of flammable liquids should be safe .Bins should be provided for
waste. Staff should be informed about the proper procedures.
3 All exits should be clear at all times.
4.Provide emergency lights in the premises.
5 Provide Fire Exit signage to clearly identify exit routes.
6 Introduce fire detectors and carry out regular testing of fire alarm system.
7 Fire extinguishers should be mounted on walls at proper heights and locations.
8 Proper training should be provided to some employees in the use of fire
extinguishers.
9 Carry out a fire evacuation drill to determine suitability of arrangements and keep
records.
10 Provide refresher fire safety training to all staff to bring to their attention the fire
precautions and evacuation procedures for the premises. Keep a record of training.[6]

3. Legislations

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The Dangerous Substances Explosives Atmospheres Regulations (DSEAR) and the
European directives for controlling explosive atmospheres and the standards of
equipment and protective systems (ATEX) are used in this risk assessment.
Below is the brief overview of each legislation used in the above risk assessment
process.
DSEAR [1]

DSEAR stands for the Dangerous Substances and Explosive Atmospheres Regulations
2002.

Dangerous substances can put peoples’ safety at risk from fire and explosion. DSEAR
puts duties on employers and the self-employed to protect people from risks to their
safety from fires, explosions and similar events in the workplace, this includes
members of the public who may be put at risk by work activity.

According to DSEAR dangerous substances are any substances used or present at work
that could, if not properly controlled, cause harm to people as a result of a fire or
explosion. They can be found in nearly all workplaces and include such things as
solvents, paints, varnishes, flammable gases, such as liquid petroleum gas (LPG), dusts
from machining,sanding, or any other kind of operations and dusts from foodstuffs.

According to DSEAR it is the employer’s responsibility to carry out risk assessments
and take the suitable actions and controls to ensure a safer workplace for the workers
and the public.

In this risk assessment the most important regulation of DSEAR is regulation 7, which
explains the classification of places where explosive atmospheres may occur, criteria
for the selection of equipment and protective systems are mentioned, and warning
signs for places where explosive atmospheres may occur..

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ATEX [2],[3]

ATEX is the name commonly given to the framework for controlling explosive
atmospheres and the standards of equipment and protective systems used in them. It is
based on the requirements of two European Directives.

It is based on the requirements of two European Directives.

1) Directive 99/92/EC (also known as ‘ATEX 137’ or the 'ATEX
Workplace Directive’) on the minimum requirements for improving the
health and safety protection of workers potentially at risk from
explosive atmospheres.
2) Directive 94/9/EC (also known as ‘ATEX 95’ or ‘the ATEX Equipment
Directive’) apply to all equipment intended for use in explosive
atmospheres, whether electrical or mechanical, and also to protective
systems. Safety devices intended for use outside explosive atmospheres
which are required for or contribute to the safe functioning of
equipment or protective systems with respect to risks of explosion are
also included. This is an increase in scope compared to former national
regulations for equipment and systems intended for use in potentially
explosive atmospheres. In Great Britain, the requirements of the
Directive were put into effect through the DTI’s Equipment and
Protective Systems Intended for Use in Potentially Explosive
Atmospheres Regulations 1996 (SI 1996/192).

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Coursework 2

The instrumentation required for pneumatic conveying of powder is proposed.

1. Introduction:
As we know that special care must be taken in selecting the equipment in hazardous
areas. There are certain limits of temperature, flow and pressure beyond which the
explosive atmosphere may formed inside the plant for example excessive increase of
the pressure inside the pipeline may cause a leakage or explosion of pipeline
.Therefore it is required that to control the temperature, flow and pressure values,
certain measuring instruments are used to monitor temperature ,mass flow of air and
pressure precisely under the rules of ATEX.

1.1.Zones:
The zones are divided as follows
-All the plant except air supply is in zone 20 and category 1 equipment is required.
-Air supply from compressor is in zone 22 and category 3 equipment is required.
-The filling area of powder is in zone 21 and category 2 equipment is required.
-Workplace is in zone 22 and category 3 equipment is required.

2.Instrumentation System in Safety respect:

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Temperatur Earthing
e meter

Temperature
Load cells
meter T1

P4
Earthing
Pressure
meter
T2

P1

Earthing P2

Mass Flow
Meter1 F1
Air

Figure 1: Proposed measurement system

Firstly for tempreture,mass flow and pressure measurements we need to identify the
areas of the plant where these measurements are required.

Since the air cylinder has compressed gas hence excessive pressure may cause to
leakage of air and become the source of oxidant.Also the gas line should be monitor
for pressure so that it must not increase the maximum pressure limit of gas pipe .Hence
pressure should be monitor for air cylinder continuously. To measure the pressure at
cylinder outlet we are using pressure meter P1 as shown in figure 1.Also the outlet of
nozzle bank connected to the pipeline should also be monitor for pressure using P2
pressure meters as shown in figure 1.P2 is used for measuring pressure for transferring
the powder to receiving vessel. The pressure at P2 should not increase to 15 barg;

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which is 1.5 times the MEP of powder which is 10 barg because the dust pipeline
maximum explosion pressure is 1.5 to 2 times the MEP of powder.
If it will increase above to this limit then an alarm will be switch on and if it becomes
equal to 2 times than the air supply will be closed.As we know that to transfer powder
to the receiving vessel we need certain pressure of air below which the powder does
not transfer to the receiving vessel. Also required pressure would be different for
different size of powder particles for example thick particles need more pressure to
transfer from blow tank to receiving vessel. P4 meter can be used to monitor the
pressure of pipeline contains dust as shown in figure 1.

The temperature of air must also be monitor to make sure that its temperature must not
increase maximum temperature limits and become the ignition source for the
powder.T2 can be used to monitor temperature for air as shown in figure 1.

To control the fire and explosion inside the pipeline it is required to continuously
measure the temperature of mixture of air and powder inside the pipeline otherwise it
will provide the ignition source for the powder and may become explode for example
smouldering may produce frictional heat and can provide ignition source or collision of
particles at the bends may cause to rise the temperature and become ignition source.So
to monitor and control the temperature of pipeline we proposed T1 meter and
transmitter which will continuously monitor the temperature and feedback the signal to
the controller which switch on alarm when the temperature will be near to its limits and
shutoff the air supply if system will deviate to these limits.

There are two mass flow measurements are required.Firstly for mass flow
measurement of air supply to the powder transferring pipeline F1 as shown in figure1
as it will measure the amount of air required to transfer powder from nozzle bank to
the receiving vessel for example if we want to measure amount of air for 1 Kg of
Pharmex we can do it by increasing the pressure from nozzle bank and measure the
flow at which the powder will transfer to the receiving vessel.
Also to measure the average mass flow of powder to the receiving vessel load cells are
used as shown in figure 1.
Moreover a PLC based system is proposed for complete automation of plant.

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2.1.Instrumentation System Design:
Due to the high demand and advantages of digital transmission over analog
transmission an instrumentation system using Profibus is proposed.Therefore all the
devices i.e., sensors and transmitters using in the instrumentation system are Profibus
based.Also only those devices have beed selected which are satisfying the ATEX
certification for the required Zones and given material.Since we are dealing with Zone
20 in the plant hence we have onle used equipment 1 category devices for example in
air measurements ATEX II 1 G devices are used and in dust measurement ATEX II 1
D devices are used in the given application.

Below is the selection of some sensors and transmitters for instrumentation &
measurements.Moreover some recommendations are proposed to replace the manual
control by automatic control.

1. Pressure measurement
The use of Endress+Hauser Cerabar S, PMP75 (endress.com) with metal sensor and
Profibus PA protocol is proposed . These are high performance pressure sensors for
extremely accurate and reliable measurements for gases and fluids with turndown ratio
up to 100:1 and measuring range from 100mbar to 700 mbar.The selected sensor is
ATEX certified from equipment 1 to equipment 3 category for gases or dust. As the
plant operated in zone 20 hence we have selected ATEX II 1 G for air pressure
measurement (P1,P2 and P3) and ATEX II 1 D for the dust (P4) .

Figure 2: Cerabar S, PMP75 Pressure Transmitter ATEX II 1 GD

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2. Temperature sensor [5]

We are required to measure temperature at the mixture of air and powder pipeline
which is in zone 20.Hence we are required temperature transmitter with certification of
ATEX II 1 D.For the given application we propose the Field mounted Temperature
Transmitter ABB TF212-Ex (abb.com) with Profibus PA output.Input ranges from
RTD,Thermocouples ,resistance and voltages.

Field transmitters are applied where the highest demands are made on safety, robust
ness and comfort .It is available in ATEX II 1/2 G/D for flame proof and dust
explosion proof with intrinsically and non intrinsically safe type. It has extended long
term stability and linear output signal with extended self diagnostics having 1 or two
input channels.

This dual-sensor input capability allows the transmitter to accept simultaneous input
from two independent sensors. This dual-sensor configuration can be used for
measuring differential temperatures, averaging temperature or redundant temperature
measurement.

Figure 3:ABB TF212-Ex Temperature transmitter ATEX II 1 D

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3. Air Mass Flow measurement

The coriolis meter is preferred for mass flow measurements in Zones 0,1,20,21
according to ATEX [3]. If a moving mass is subjected to an oscillation perpendicular
to its direction of movement, Coriolis forces occur depending on the mass flow. A
Coriolis mass flowmeter has oscillating measuring tubes to precisely achieve this
effect.

The sensing element is a vibrating tube, through which the fluid flows.

Figure 4:Coriolis Flow Measuring Principle

The use of Endress + Hauser Promass 80 F (endress.com) universal mass flow
transmitter having Profibus output is proposed.The selected sensor is ATEX certified
for all zones and for gases and dust as well.Since we are measuring the mass flow of
air in zone 20 hence we have selected EX II 1 G for the given application respectively
in the places of F1 in the figure 1.

Some characteristics for the transmitter are
• The direct mass measurement
• Is independent of conductivity, density, pressure or temperature of the fluid.
• High accuracy for liquids and gases
• No moving parts

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Figure 5: Mass Flow meter ATEX II 1 GD

Measuring Mass Flow rate of Powder:
In order to measure mass flow rate of powder from blow tank to receiving vessel we
used two load cells measuring weight of powder.
It works by measuring the weight of powder and sends the signal to the PLC which
measures the avarage mass flow rate by dividing the weight of powder by unit time in
the control program and taking average.
The Load cell can be equipment 3 because the load cell are attached to outside the
receiving vessel as shown in the figure below and the zone outside the plant is 22.

Load Cell Load Cell 2

Figure:Load Cells for measuring Mass flow rate

Load cells should be calibrated and Atex certified.

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Measuring Temperature of Gas:
To make sure that the air going to the blow tank from compressor is not hot we can use
a temperature transmitter of equipment 3 category as the air supplying part is in zone
22.
3. Control system Recommendations:
3.1.Automatic control of powder mass flow rate through Nozzle bank :
It is proposed to replace the manual control of air pressure through nozzle bank by
feedback control system.It can be achieved by replacing manual valve with analog
solenoid valve control by the PLC.
It works as follows
-taking the user defined input of mass flow rate between minimum and maximum limit
from the input panel
-Taking feedback signal of mass flow rate of powder through load cells.
-and then finally setting the solenoid valves until the desired mass flow rate will not
achieved.

For automatic control of nozzle bank we require Equipment 3 category of solenoid
valves as we are in zone 22 in nozzle bank side i.e.,ATEX II 3 G .

3.2.Controlling compressor air supply :
To control compressor air pressure it is proposed to use analog solenoid valve.It works
as follows:
-it takes signal from PLC.
-The feedback signal can be blow tank pressue,pipeline pressure.

The valve should be category 3 if the compressor is in the same room or could be any
if in the separate room.

3.3.Automatic filling of powder in the blow tank:
It is recommended to use automatic filling of powder in the blow tank.
To achieve this a level sensor can be used to monitor level of powder inside blow
tank.

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The level sensor must be of equipment 1 category since blow tank is in zone 20.
The system works as follows:
-If level of powder is less than the minimum level then firstly the PLC stops the
compressor supply and waits until the powder stored in the tank starts filling up to
defined level and the PLC runs the compressor supply again.
The supply of powder to the blow tank can be control by using a digital solenoid valve
of equipment 1 category as it may be in zone 20.A proximity sensor of equipment 22
category can be used to send the position signal of solenoid valve to detect fault of
solenoid valve.

3.4.Controlling Powder level in receiving vessel:
The level of powder inside the receiving vessel can be control by measuring the weight
of powder inside the receiving vessel to make sure that the powder will not exceeds
from the maximum level i.e if the receiving vessel continue to accept filling the
powder then if the powder exceeds from the desired level it may be dangerous or cause
faults in the plant.

To monitor level the load cells are calibrated with the level and give signals to the PLC
and the PLC stops the air supply if the level will become to the maximum value by
give stop signal to compressor outlet and shutoff compressor.

3.5.Programmable logic controller (PLC) :
The heart of this control system is the PLC which receives signal from plant and sends
control signals to the plant to control the plant.The PLC should be away from plant or
if possible should be in other room.If in the same room as in which the plant is then the
PLC should be places inside the cover to safe it from explosion.

3.6.Graphical User Interface (GUI):
It is proposed to use the computer for graphical user interface .The Pc would be
connected to the PLC and gather data from PLC.A GUI would be used to display data
and alarm signals.

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The computer should be either in the room other than plant or if in the same workplace
then computer should be place inside the cover so that it will resist itself in case of the
explosion.

3.7.Redundant system:
In case of power failure a backup system is provided to power up the PLC and the
computer.
In case of PLC failure the plant must shut down.

3.8.Smoke & Fire Detectors:
It is recommended to use fire and smoke detectors inside the room of category 3 in
zone 22.
An emergency shutdown system should be provided in case of fire and explosion.

4. Proposed Instrumentation System Architecture:
It is recommended to use programmable logic controllers (PLC) based process control
system for controlling the given pneumatic coveying system.Moreover it is proposed to
use higher commuinication network like Ethernet or TP/IP for network access or even
WEB.The block diagram of the implemented system may be as follows.

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Figure 6:Proposed Instrumentation system Architecture

5. Legislations in selecting the Equipments:
Equipment and devices are selected in agreement with regulation 7 of DSEAR [1] and
ATEX as explained in the coursework 1.

5.1. Equipment Groups and categories [7] :

There are two equipment groups defined in the EPS Regulations. Equipment Group I
is equipment intended for use in underground parts of mines, and to those parts of
surface installations of mines, liable to be endangered by firedamp and/or combustible
dust. Equipment Group II is equipment intended for use in places, other than those
specified for Equipment Group I, liable to be endangered by explosive atmospheres.

Under ATEX 95 equipment is categorised as below:

Mining equipment –

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• Group I, Category M1 – very high level of protection, equipment may continue
to operate in the presence of explosive atmosphere
• Group I, Category M2 – high level of protection, equipment to be de-energised
in presence of explosive atmosphere.

Non-mining equipment -

• Group II, Category 1 – equipment suitable for Zones 0, 20

REFERENCES
[1] http://www.hse.gov.uk/fireandexplosion/dsear.htm
[2] http://europa.eu.int/comm/enterprise/atex/guide/guidesec_en.pdf
[3] http://www.hse.gov.uk/fireandexplosion/atex.htm
[4] http://www.endress.com/corporate
[5] http://www.abb.com/product/seitp330/c1256ccb004e516cc1256ab0004422dd.aspx
[6] http://www.infoscotland.com/firelaw/files/RA_5.pdf
[7] http://www.hse.gov.uk/electricity/atex/definitions.htm

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