fire engineering principles workbook · fire risk consultancy limited, cade house, 12 high street,...

Fire Risk Consultancy Limited, cade house, 12 High Street, Molesworth, Huntingdon PE28 0QF. www.frconline.co.uk [email protected] 01832 710770

The aim of this course is to enable the student to understand fundamental Fire Engineering Principles. It will give you the basic principles and underlying principles you need to carry out a Fire Engineered solution. It will also go through fundamental mathematical principles that Fire Engineers should have.

Fire Engineering Principles Workbook

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Page

Module 1 Basic principles of Fire Engineering 3

Module 2 Determining fire size 4

Module 3 Misconceptions 4

Module 4 What is CFD modelling? 4

Module 5 Fire modelling 4

Module 6 Case studies 5

Module 7 Application of fire modelling 5

Module 8 Fire Engineering strategy 5

Module 9 Shopping mall engineering strategy 5

Module 10 Block of flats Engineering strategy 6

Module 11 Smoke control strategy for care premises 6

Module 12 Full Fire Strategy 1 6




Module 16 The Cone Calorimeter 6

Module 17 Porta level 7

Contents

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Module 18 Timber framed analysis 1 7



Module 21 Probabilistic analysis 7

Module 22 Bernoulli principle 13

Module 23 Question1 14

Module 24 Question 2 15





Module 29 Dimensional analysis 20

Module 30 Differentiation 24

Module 31 Integration 1 28

Module 32 Integration 2 28

Module 33 Fires in compartments 1 40




Module 37 Sprinkler calculations 1 58

Module 38 Sprinkler calculations 2 58

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This module will look at the principles of fire engineering and the core competencies that a fire engineer should possess.

Module 1

This module covers the following topics:

• Basic principles of Fire Engineering • History of Fire Engineering • What is Fire Engineering? • Role of Fire Engineer • Fire Engineering approaches available • Fire Engineering Competence

.

Module 1 Fire Engineering introduction

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.

Module 2


• Determining fire size • Design approaches • Liaison with Fire Service • Advantages of Fire Engineered Solution • Disadvantages of Fire Engineered Solution • Are some Fire Engineered Solutions flawed? • Guidance documents • Main factors to consider with Fire Engineered solution

.

.

Module 3


• Misconceptions • What if? • Qualitative Design Review • Published documents • Assessment against criteria • Competencies

Module 4


• What is CFD modelling • Case Studies

Module 5


• Fire Modelling • FDS • Impulse fans • Smoke control in flats - CFD • Various CFD Models • CIBSE Guide E

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Module 6


• Case Studies

.

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Module 7


• Reconstruction using fire modelling • Application of fire models • Issues with smoke control in blocks of flats

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Module 8

This module covers the following topics;

• Fire engineered strategy introduction

Module 9


• Fire engineered strategy for shopping complex

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Module 10


• Fire engineered strategy for block of flats

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Module 11


• Fire engineered strategy for smoke control system to be installed in a care premises

Module 12


• Full fire engineered strategy using a performance base approach Part 1

Module 13



Module 14



Module 15



Module 16


• The cone calorimeter

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Module 17


• The porta-level

Module 18


• Timber framed analysis 1

Module 19



Module 20



Module 21


• Probablistic analysis

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Daniel Bernoulli was a Dutch born Swiss Scientist, who discovered basic principles of fluids. The Bernoulli principle is that a fluid (liquid or gas) in motion can have three types of energy

• Potential energy

• Kinetic energy

• Pressure energy

These can be interchanged but unless energy is taken out (e.g. turbulence or friction) or energy is put in (e.g. pump) then the total energy must be constant.

The frictional loss is neglected in calculations due to being small compared to the total energy, however, you must consider frictional loss in certain circumstances e.g. sprinkler calculations

To use Bernoulli’s theorem in calculations it is important to have all three forms of energy in the same units. The Systems International (SI) unit for energy is the Joule (kg.m2/s2) however; when using Bernoulli the energy is expressed per unit mass or per unit volume.

Therefore, there are different forms of the Bernoulli Equation depending on whether we are working with either joules per kilogram (j/kg) or joules per meter cubed (j/m3). In order to simplify the matter, I am only going to use the Bernoulli Equation that expresses the energy in the form of joules per metre3 (j/m3) which I believe is easier to apply to IFE examination questions.

Potential energy

This is the energy due to the potential above the datum line from which all the energies are measured. The potential energy per m3 of fluid can be considered as

ρgo (Joules/m3)

Where

p = density (kg/m3)

g = acceleration due to gravity (9.81 m/sec2)

H = height (m)

Kinetic energy

The kinetic energy is due to the fluid being in motion. The Kinetic energy can be considered as

½ ρv2 (Joules/m3)

Where p = density (kg/m3)

Unravelling the mystery surrounding Bernoulli’s

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V = Velocity (m/sec)

Pressure energy

The pressure energy is due to being under pressure. The SI unit of pressure is Pascal but in the Fire Service, the Bar and metres head are still used. Therefore, you must remember to use the correct formula

To convert from Bar to Pascal’s you use the following

P X 100,000 (Joules/m3)

Where P = Pressure (Bar)

To convert metres head pressure to Pascal’s, you use the following

ρgz (Metres head) (Joules/m3)

Where ρ = Density (kg/m3)

g = acceleration due to gravity 9.81 m/sec2

z = height (m)

Bernoulli – Pascal’s

Where the pressure energy is Pascal’s

PA + ρgHA + ½ ρvA2 = PB + ρgHB + ½ ρvB

2

Where PA is pressure energy at point A (joules)

ρgHA is the potential energy at point A ( joules)

ρ = Density of fluid (kg/m3)

g = Acceleration due to gravity 9.81 m/sec

H = height of column of water

½ ρvA2 is the kinetic energy at point A (joules)

V = velocity m/sec

Where the pressure energy is Bar

PA x 100,000+ ρgHA + ½ ρvA2 = PB x100, 000+ ρgHB + ½ ρvB

2

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Where the pressure energy is metres head

ρgzA + ρgHA + ½ ρvA2 = ρgzB + ρgHB + ½ ρvB

2

Continuity equation

When considering Bernoulli it is also very important to understand the continuity equation. This is due to the fact that in a closed system the rate of flow Q (m3 /sec) can be considered as constant.

Q = VA

Where Q = Rate of flow (m3/sec)

V = Velocity (m/sec)

A = Area (m2)

If the flow is constant then

Q = VAAA = VBAB

This is shown here in this diagram showing a pipe

As the water flows down the pipe and it tapers out what you will find is that the waters velocity will reduce. In other words as the area increases the velocity falls. This is a very important relationship when attempting Bernoulli calculations as will be shown later. Before we attempt questions involving the use of these equations, I would like to give you a few tips to ensure mistakes are not made.

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Tip one

Produce a sketch and enter all the details given in the question first. This will make understanding the problem much clearer.

Tip two

Always convert ALL units to SI units before attempting to answer the question. Many candidates make mistakes because they don’t convert the units and simply place the number in the formula.

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Here is a list of the most common units.

SI unit

Length (L) m

Area (A) m2

Velocity (V) m/sec

Acceleration due to gravity (g)

9.81 m/sec2

Height (h) m

Metres head (z) m

Energy (joule) kg.m2/s2

Pressure (Pascal) n/m2

Volumetric flow (Q) m3/sec

Tip three

You have to place a datum line which is where you are measuring the energies from. Now if this is a horizontal pipe you always put the datum in the centre of the pipe because in this way you have zero potential at both points. This is because the potential energy above and below the datum cancels out. Now if the situation is not in a horizontal pipe for example like this example.

What you do is always place your datum line at the lowest point in the system. In this way only one of the points will have potential energy and it makes it easier to answer the question.

Module 22


• Bernoullis theorem (principles)

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Module 23


• Question 1

Question 1

A pump is pumping 2m3/min of water the surface of which is 5m below the pump inlet. At the outlet the pump has a diameter of 100mm and at this point the pressure is 8 Bar. From the nozzle (which is at the same level as the pump outlet) the jet rises 35m.

A) Calculate the energy/kg of the water

(1) At the outlet of the pump (2) At the top of the throw of the jet

B) Explain why (1) and (2) are not equal

(acceleration due to gravity is 9.81m/sec2)

Bernoulli’s Exercises

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Module 24


• Question 2

Question 2

Water is flowing horizontally through a 250mm diameter pipe and into a constriction of 100mm diameter. The pressure difference is measured as 23.5mm of mercury. Using Bernoulli’s theorem, calculate the rate of flow.

(Density of mercury = 13,600 kg/m3)

(Density of water = 1000 kg/m3)

( g = 9.81)

Pressure difference = 23.5mm mercury

Density of mercury = 13,600 kg/m3)

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Module 25


• Question 3

Question 3

A foam generator consists of a horizontal tube of circular cross section which tapers from an input of 80mm internal diameter to 20mm diameter. 750 lts/min of concentrate (Density 1200 kg/m) is flowing through the generator and the pressure inlet is 12 Bar.

What is the pressure at the point where the diameter is 20mm?

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Module 26


• Question 4

Question 4

Water is flowing in a vertical tapering pipe 2 metres in length. The top of the pipe is 100mm diameter and the bottom is 50mm diameter. The quantity of water flowing is 1300 litres/minute.

Calculate the pressure difference between the top and the bottom of the pipe?

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Module 27


• Question 5

Question 5

A pump supplies 4kw of energy to the water flowing through a 45mm hose. The water flows 15m vertically and through a 25mm branch at a rate of 500 litres/minute. Use Bernoulli’s theorem and find the pressure at the branch.

Make a sketch and fill all details as shown here

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Module 28


• Question 6

Question 6

If the manometer readings are 800mm and 200mm, what is the flow ?

(Density of water = 1000kg/m3)

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Dimension analysis

Module 29


• Dimensional analysis

Question 1

Determine the dimensions of the constant a?

2atQ

Where Q = Heat release rate (kW)

t = seconds (s)

Question 2

Determine the dimensions of the parameter R?

RHQ C

Where Q = Heat release rate (Kj.s-1)

Hc = Heat of combustion (kg.s-1)

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Question 3

Determine the dimensions of the parameter T ?

)/(0 PPm McQTT

Where QP = Heat release rate (Kj.s-1)

M = Mass flow rate (kg.s-1)

Cp = Specific heat capacity (kj.kg-1.K-1)

Question 4

Determine the dimensions of the Stephan boltzman constant ?

4

ffr TI

Where Dimensionless

Dimensionless

Ir = Radiative heat flux (kW.m-2)

Tf = Temperature (K)

Question 5

Determine the dimensions of the froud number Fr?

gl

UFr

Where U = Velocity (m.s-1)

g = Gravity (m.s-2)

l = Specific heat capacity (m)

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Question 6

Determine the dimensions of the parameter H c?

c

fH

Qm

Where mf = Mass flow rate (kg.s-1)

Q = Gravity (kj.s-1)

Question 7

Determine the dimensions of the parameter qK ?

f

Cck

A

Hmq

Where mc = Mass (kg)

Hc = Calorific value (mj.kg-1)

AF = Floor area (m2)

Question 8

Determine the dimensions of the parameter Q?

cf HmQ

Where mf = Mass flow rate (kg.s-1)

= Calorific value (kj.kg-1)

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Question 9

Determine the dimensions of the parameter qK ?

2/52/1

00

*

sp DgTc

QQ

Where Q = Heat release rate(kj.s-1)

Cp = Heat capacity (kj.kg-1. K-1

P0 = Ambient air density (kg.m-3)

T0 = Ambient air temperature (k)

g = Acceleration due to gravity (m.s-2)

Ds = Linear dimension (m)

Question 10

Determine the dimensions of the parameter D?

t

bm

V

fDD

Where Dm = Mass optical density (m2.kg-1)

Vt = Total volume of smoke (m3)

fb = Total mass of fuel (kg)

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Differentiation

In this module we are going to look at differentiation.

Module 30


• Differentiation

Differentiate the following formula

Exercise 1

2xy

Exercise 2

3xy

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Exercise 3

5xy

Exercise 4

10xy

Exercise 5

2 xy

Exercise 6

5 xy

Exercise 7

2/11xy

Exercise 8

3/13xy

Exercise 9

4

1

xy

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Exercise 10

2

1

xy

Exercise 11

4651 43

3 xx

xy

Exercise 12

71191 82

5 xx

xy

Exercise 13

82 xxy

Exercise 14

96 2xxy

Exercise 15

210 xy

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Exercise 16

xxy 3

Exercise 17

xxy 84 4

Exercise 18

xxxx

y 52

32

1

Exercise 19

xxxx

y 510

88

1

Exercise 20

5.35.4 4 xxy

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Integration

In this module we are going to look at integration

Module 31


• Integration 1

Module 32


• Integration 2

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Exercise 1

Determine the integral of the following?

6)( xF

Exercise 2


7)( xxF

Exercise 3


10)( xxF

Exercise 4


410)( xxF

Exercise 5


128)( xxF

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Exercise 6


xxF

1)(

Exercise 7


xexF 2)(

Exercise 8


xexF 4)(

Exercise 9


xexF 3)(

Exercise 10


xexF 2)(

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Exercise 11


dzzzz 23 648

Exercise 12


dzzzz 34 1259

Exercise 13


dzzzz 78 423

Five steps

Step 1 – Turn into form you can integrate

Step 2 – Integrate the formula

Step 3 – Substitute in the point you are given as x and y

Step 4 Solve for C

Step 5 – Write down final answer with C in correct place

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Exercise 14

Determine the integral of the following when you know that the curve goes through the point

(3,2)?

xxx

dx

dy 322

2

Exercise 15


(4,6)?

32 xxxdx

dy

Exercise 16


(1,1)?

23 5.246 xxxdx

dy

Exercise 17


(2,3)?

23 2124 xxxdx

dy

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To integrate when you have simple limits you use the following method.

Step 1 Integrate as normal, however don’t add the C but put the results in square brackets

showing the limits

Step 2 Substitute the top limit in and evaluate it

Step 3 Substitute the bottom limit

Step 4 Subtract the value to find the answer

Exercise 18


xdxx 5

2

2 25.3

Exercise 19


xdxxx 3

4

1

25.0

Exercise 20


xdxxx 2

11

4425.0

Determining area under graph

Step 1 – Write down in form of integral

Step 2 – Integrate the formula

Step 3 –Evaluate it

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Exercise 21

Determine the area under the following curve between x =1 and x = 8?

dxxxy 37 3

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Exercise 22


xdxxxy 234 23

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Exercise 23


dxxxy 5146 2

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Exercise 24

Determine the mass flow rate of smoke out of an opening 0.5m high x 1.2m wide with a slow

growing fire in a banking hall over 1 minute 30 seconds?

0

3/12

00 09.0 hwQm p

Using

90

0

3/53/1

0

3/2

0

60

00

5

309.0

tahwdtm

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Exercise 25

Determine the mass flow rate of smoke out of an opening 0.34m high x 1.6m wide with a FAST

growing fire over 2 minute 15 seconds?

0

3/12

00 09.0 hwQm p

Using

135

0

3/53/1

0

3/2

0

135

00

5

309.0

tahwdtm

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Exercise 26

a) Determine the mass flow rate of smoke out of an opening 0.28m high x 3.4m wide with a

FAST growing fire in the first 2 minutes of fire development.

b) What would it have been if the fire growth rate was ultra-fast instead?

0

3/12

00 09.0 hwQm p

Using

135

0

3/53/1

0

3/2

0

135

00

5

309.0

tahwdtm

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Compartment fires

This module will cover the issue of Fires in Compartments

Module 33

At the end of this presentation you will have a good understanding of:

• Introduction • Stages in compartment fires • Ceiling jet

.

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Fires in Compartment Fires

Legions Of Armed Romans Tend to Fight Quickly

L Locate the sprinkler, heat or smoke detector from seat of fire

O Determine the operating temperature of the device

A Use Alpert’s equations to determine time to operate and velocity of gases

R Determine RTI and apply it to determine thermal lag

T Determine actual time for sprinkler operation by adding thermal lag to output from step 3

F Determine the actual fire size on sprinkler, heat or smoke operation

Q Determine the quantity of water required to control fire

3/5

.3/2

0 9.16H

QTT 18.0

H

r

18.0H

r

H

rQ

TT

3/2.

0 38.5

3/1.

96.0

H

QU

15.0H

r

15.0H

r

6/5

.2/13/1

195.0r

HQU

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Exercise 1

Determine the temperature of the hot gases and gas velocity of a wall ceiling jet at a heat detector located at 0.2m from the plume in a room with a height from the base of the fire to the ceiling of 3.2m? The fire size is 450kW.

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Exercise 2

Determine the temperature of the hot gases and gas velocity of a corner ceiling jet at a heat detector located at 0.5m from the plume in a room with a height from the base of the fire to the ceiling of 3m? The fire size is 250Kw.

Exercise 3

Determine the temperature of the hot gases and gas velocity of an axi-symmetric ceiling jet at a heat detector located at 2.6m from the plume in a room with a height from the base of the fire to the ceiling of 4.6m? The fire size is 570kW.

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Module 34


• Fire Size • 7 Step Guide • Exercises

.

Module 35


• Exercises utilising the 7 step guide

.

Exercise 4

Determine the fire size at the time the sprinkler operates in the following situation?

• Fast response sprinkler colour -red

• Assume ambient temperature is 293K

• Occupancy is a shop (fast fire growth from BS9999).

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Exercise 5

Determine the fire size at the time the heat detector operates in the following situation?

• Operating temperature of the heat detector = 70C

• RTI of heat detector = 12 Spacing of heat detectors = 15m

• The height from the base of the fire to the ceiling of 11m.

• ambient temperature is 293K

• Occupancy - shop (fast fire growth from BS9999)

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Exercise 6

A natural smoke control system is proposed for a large warehouse undergoing refurbishment with the following parameters.

• The sprinkler head is red with a fast response sprinkler head with a spacing of 4.5m



• The building is to store contents with a medium fire growth.

a) Determine the fire size at sprinkler operation?

b) If the building was used to store products with an ultra-fast fire growth rate, how would that affect the fire size on sprinkler operation?

c) What would have been the impact of the sprinklers were standard response with an RTI of 120 for the ultra-fast fire growth?

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Exercise 7


• Fast response sprinkler is coloured red with a spacing of 8m

• The height from the base of the fire to the ceiling of 7.5m.


• Occupancy is a banking hall (slow fire growth from BS9999)

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Exercise 8


• Standard sprinkler (RTI = 90) is coloured green with a spacing of 6.5m

• The height from the base of the fire to the ceiling of 5.6m.


• Occupancy is a bingo hall (medium fire growth from BS9999)

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Exercise 9


• Standard sprinkler (RTI = 90) is coloured red with a spacing of 9.0m



• Occupancy is a storage building (ultra-fast fire growth from BS9999)

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Exercise 10

A fire risk assessor identifies that a sprinkler system has been incorrectly fitted with standard response sprinklers with an RTI of 120, when it should have been fitted with fast response sprinklers, can you determine the impact on the fire size at time of sprinkler operation?

• The sprinkler head is yellow with a spacing of 6.0m



• Occupancy is a storage building (fast fire growth)

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Module 36


• Interaction between smoke vents and sprinklers • Single opening in compartment • Heat release rate required for flashover

Single opening into compartment.

When there is a single opening in the compartment you can determine the temperature increase of the gases using the following formula.

3/1

2/1

0

2

85.6

Tko

gAhhA

QT

gT = Increase in temperature of gas K

Q = Heat release rate (kw)

Ao = Area of ventilation opening (m2)

h o = height of opening

h k = Effective heat transfer coefficient (kw/m2.K)

AT = Total area of compartment enclosing surfaces(m2)

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Firstly, determine if thermally thick using the following formula

wall

wallwallwallp

Ct

2

2

If the time is less than tp then use formula 1 if not use formula 2

Formula 1 t

CpKhK

Formula 2 wall

wallk

kh

Exercise 11

Calculate the upper layer temperature of a room 4.7m x 3.4m in floor area and 2.7m high.

There is a door opening 2.0m high and 1.0m wide.

The fire source is steady 1250Kw FIRE.

The wall lining material is 0.02m ceramic fibre insulation board plaster

(k wall = 0.00055kW/m.K.

c wall = 0.960 kJ/kg.k.

p wall = 800 kg.m-3.

Perform the calculations at time 20, 60 and 120 seconds after ignition.

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Exercise 12

Calculate the upper layer temperature of a room 8.4m x 4.2m in floor area and 3.2m high.

There is a door opening 2.1m high and 2.1m wide.

The fire source is steady 750Kw FIRE.

The wall lining material is 0.02m ceramic fibre insulation board plaster

k wall = 0.00055kW/m.k .

c wall = 0.960 kJ/kg.k.

p wall = 900 kg.m-3.

Perform the calculations at time 30, 60 and 180 seconds after ignition.

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Time to flashover

Babrauskas 1980

2/1

0

.

600 HAQFO

Hagglund 1981

3

2/1

.

247.0)/(

2.11050

HAAAQ

Ot

tFO

McCaffrey 1981

HAAhQ TKFO 0

.

740

Thomas 1981

2/1.

3788.7 HAAQ OTFO

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Exercise 13

Determine the heat release rate required to cause flashover for the following building with a single opening using the four models available?

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Example 14


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Example 15


.

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Sprinkler Calculations

This module will look at the methodology for determine the pressure and flow requirements of sprinkler systems to BS EN 12845. To carry out the exercises you do need access to a copy of the standard.

Module 37


• Overview • Extent of sprinkler protection • Hazard classification • Area of operation

.

Module 38


• Exercises

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Exercise 1

Determine the pressure and flow requirements of a sprinkler set used to protect an area which

is classified as OH2

and they are using 32mm cast iron pipework. The sprinklers are spaced 3.0m apart. There is a 90 degree screwed elbow in the pipework system and a rise of 6.5m above the valve. The K value of the sprinkler is 115.

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Exercise 2

a) Determine the pressure and flow requirements of a sprinkler set used to protect an area which is classified as LH and they are using 20mm steel pipework. The sprinklers are spaced 4.59m apart with each sprinkler covering 21m2. There is a 45 degree screwed elbow in the pipework system and a rise of 3.4m above the valve.

b) What would the flow and pressure required at the valve have be have been if you had used 25mm steel pipework

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Exercise 3

a) Determine the pressure and flow requirements of a sprinkler set used to protect an area

which is classified as high hazard for roof sprinklers. As the contents are mixed, choose the

highest HH standard.

They are using 40mm steel pipework. The sprinklers are spaced 3m apart with each sprinkler covering 9m2. There is a 90 degree screwed elbow in the pipework system and a rise of 8.6m above the valve. The K value of the sprinkler is 115.

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