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 CHEMICAL ENGINEERING TRANSACTIONS  
 

VOL. 82, 2020 

A publication of 

 
The Italian Association 

of Chemical Engineering 
Online at www.cetjournal.it 

Guest Editors: Bruno Fabiano, Valerio Cozzani, Genserik Reniers
Copyright © 2020, AIDIC Servizi S.r.l. 
ISBN 978-88-95608-80-8; ISSN 2283-9216 

Analysis of the Operational Risk of the Process Pasteurization 
and Mixing in a Dairy Processing Plant, Using the HAZOP 

Methodology  
Angie Montaño, Yeferson Torres, Eddy Herrera, Johan Rincon, Pablo Velasquez, 
Angelica Santis* 
Universidad Cooperativa de Colombia, Avenida Caracas 37-63, Bogota  
angelica.santisn@ucc.edu.co  

The realization of PHA (Process Hazard Analysis) as an evaluation of all those elements that are part of 
management programs for safety in industrial processes that can generate an impact on the profitability of the 
company, is a matter to highlight. Given the above, industries need to identify the variations that occur 
concerning normal parameters in the process. During the development of the study, operational risks are 
analysed in the process of a dairy plant, located in Cundinamarca, Colombia. For this analysis, the HAZOP 
methodology is used, which will allow the identification of hazards, operability study, and mitigation of the risks 
related to the investigated process. For the analysis, the pasteurization and mixing stage as the subsystem 
was determined. In this operational stage, the node to study was the reactor.  The different diagrams of the 
node for the analysis were established. The specifications at the equipment and instrumentation level were 
used. Previous information, plus the contributions regarding the operation of the plant by staff, the inputs are 
compiled for the development of the mentioned methodology. Once the deviations in the studied node were 
identified, the possible origins and effects of each deviation were determined. The measures and corrective 
actions necessary for improvements in the production process were proposed. 

1. Introduction 
For a manufacturing company, it is essential to keep control of each process in order to keep the profitability 
rates stable and the mitigation most significant possible number of operational risks. In the case of dairy 
companies, considering that their products categorized as high risk to public health, these controls must be 
more exhaustive to ensure the total quality of the products to the customer. One of the most critical processes 
in the industry is milk safety before it converts into a finished product, microbial safety must ensure to increase 
milk life; therefore, the pasteurization is the heat treatment for used to guarantee the milk safety in this 
industry. (Aouanouk, et al., 2018). With the main to ensure the continuous improvement of the company and 
the supervision of the procedure of pasteurization of the milk, it is necessary to implement the risk analysis 
process commonly known as PHA. For the realization of the PHA, there are different methodologies, among 
the most recognized and implemented is the technical what-if checklist, the analysis of the failure tree (FTA), 
modal analysis of failures and effects (FMEA), analysis of cause and consequence (CCA), analysis of event 
tree (ETA), preliminary analysis of risks (APR) and the functional analysis of operability (HAZOP) (Kunte and 
Sakthivel, 2016). The analysis mentioned above is functional; however, it is of vital importance to understand 
the resources available to be able to run it, the scope that it wants to give to the possible outcomes, the 
complexity, and stage of development of the facilities, among other factors. For this study, was chosen as 
methodology the HAZOP because of its easy application and contribution in the processes of the dairy 
industry, this analysis is based on the standard IEC 61882:2016 (IEC, 2016). 
The technique HAZOP focuses on identifying and analysing the risks and also in the methodical and 
systematic tracking of the operational deviation. Besides, this analysis achieves to determine the different 
stages that can affect the employees, environment, infrastructure, inputs, machinery, production, and other 
factors. In the same way, it is establishing the principal components that cause risks as the process 

 
 
 
 
 
 
 
 
 
 
                                                                                                                                                                 DOI: 10.3303/CET2082017 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Paper Received: 6 January 2020; Revised: 1 April 2020; Accepted: 30  August  2020 
Please cite this article as: Montano A., Torres Y., Herrera E., Rincon J., Velasquez P., Santis A., 2020, Analysis of the Operational Risk of the 
Process Pasteurization and Mixing in a Dairy Processing Plant, Using the Hazop Methodology, Chemical Engineering Transactions, 82, 97-102  
DOI:10.3303/CET2082017 
  

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distribution, the equipment, the design, human actions, lack of preventive methods, external methods, for 
these reasons is necessary to count on teams of experts that known and understand the process with the 
different risks in functioning. Later is analysed the probability and severity when the problem happens and 
then to pose a sequence of recommendations and suggestions that mitigate the damages and dangerous 
situations. Additionally, this technology is of human reasoning, and for this reason, there is not a success or 
exact solution, it depends on the knowledge and experience of human resource who applies the methods 
(Freedman, 2003). Therefore, in this case, is showed as an example of a dairy factory located in Colombia, 
where the control of operational parameters is not constant, only the factory realizes an initial inspection and 
other of the tentative way in the course of the process of pasteurization the milk. Different variables condition 
this process of integrating into all systems, and it requires a combination of time-temperature that achieves 
adequate heat treatment from microbiological and organoleptic perception milk suitable for its final treatment. 
(Gonzalez, 2013). As a result, with the methodology HAZOP, the factory can determine the operational risks 
for establishing preventive measures but also to realize a cost budget of the process and its failures. Finally, it 
concludes that this technique applies in any company and process with positive results in the identification of 
the deviation of the variable and the operational parameters of the process that carry in risk situations and 
difficulties in operation. 

2. Material and methods 
The analysis of operational risk performs at a plant of dairy, located in the municipality of Subachoque, 
department of Cundinamarca, Colombia. The method employed for the analysis, as mentioned previously, it 
was the HAZOP. It determinate as the principal subsystem for the analysis, the stage of pasteurization, and 
mixing. In this operational phase, the node-to-study was the reactor. The description of the process makes 
using a diagram P&ID shown in Figure 1.  
 

 

Figure 1: P&ID Process Pasteurization and Mixing  

The identification process of deviations and possible causes are made considering parameters such as the 
pressure, temperature, flow, among others.  A matrix with further improvements to the model proposed by  
Marhavilas et al., 2019, was created. 

3. Results and discussion 
Table 1 shows the risk matrix produced, considering the parameters for severity (S) and probability (L), and in 
Table 2, the parameters that define the probabilities of events where failures occur are presented. 

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Table 1: Risk matrix 

Ranking Severity(S) Consequences Likelihood(L) 
  Environmental 

damage 
Clients - Business 
Economics 

Personnel injury 1 2 3 4 5 

5 Catastrophic/
Fatal 

Multiple 
environments 
affected 

Loss of market share. 
> 10 million  

Single fatality or 
multiple fatalities. 
Permanent disability 

M M H H VH

4 Severe/ 
Serious 

Major localized 
effect 

Loss of sensitive or 
priority market 
customers. > 1 Million 
and <= 10 Million 

Fracture, hospitalisation 
>24 hrs, incapacitation 
>4 weeks 

L M M H H

3 Major Localized effect Shortages and / or 
loss of customers. > 
100,000 and <= 1 
million. 

Strain/twist, sprain/ 
cramp/ dislocation, 
incapacitation >= 3 
days 

N L M M H

2 Small/Minor Minor effect Complaints and / or 
Claims. > 10,000 and 
<= 100,000 

Minor injury (without 
disability), basic first-aid 
need, no-hospitalization 

N N L M M

1 Trivial/Only 
Minor 

Slight Specification non-
compliance fixed. 
<10,000 

Minor injury, discomfort, 
slight bruising, self-help 
recovery 

N N N L L

0 No impact No effect None No injury N N N N N
Risk (R): * VH:"Very High"; H:" High"; M:" Medium"; L:" Low"; N:" None" 

Table 2: Likelihood parameters definition] 

Code  Definition 
1 Remote (almost never). It has not happened in the industry. Once per 100 years 
2 Unlikely (occurs rarely). It has happened in the industry (once per 25 years) 
3 Possible (could occur, but uncommon). It has happened in the last 10 years 
4 Likely (recurrent but not frequent): once per year. Probable occurrence in a period between 1 and 5 

years 
5 Very likely (occurs frequently). It can occur throughout the year. Several times a year (once per month)
Based on the risk matrix developed, we identified the main perturbations and deviations that have the process. 
There we found that the main risks are relational with systems of flow, temperature, agitation, and lack of 
maintenance programs. Set out the consequences that can generate each risk, and the most critical were 
related to shutdowns of the process, fire, and explosions, which would imply much harm to the personal as 
economic the evaluation of the previously mentioned evidence in table 3. Besides, inside the table are set out 
the possible recommendations or solutions to mitigate the risks mentioned. 
 
Table 3: Evaluation of the risk of the node (continue) 
  
Parameter Deviation  Posible Cause  Consequences Safeguards Risk Matrix  Recommendations 
         S L   R    
Flow Low Flow The flow is 

varied, where it 
is necessary 
that the 
retention time is 
18 - 20 sec 
evenly 

The reduction of 
microorganisms 
and bacteria is 
not achieved due 
to the effect of 
the pasteurization
temperature. 
Delay in the 
process.

Regulate the 
flow. Process the 
milk again. 

3 3 M Have a follow up 
maintenance program
 
 
 
 
 
 
 

  Reverse 
flow 

Blockage / 
Breakage of 
check valves 

Blockage / 
Breakage of 
check valves 

Change of 
periodic check 
valves and 
preventive 
inspections to 
avoid production 
stoppage

 4 3 M Generate a change of 
valves in order to 
minimize obstructions 
in the process 
 
 
 

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Maintenan
ce 

Less LevelLiquid inlet 
control valve 
failure, Level 
control probe 
failure 

Variation of 
optimal operating 
conditions, 
Decrease or 
increase of the 
output flow 

Routine valve 
checks, Regular 
probe calibration

 5 2 M Automate the process 
with electrovalves 
where they are 
controlled by the 
signals emitted from 
the probes to avoid the 
variation of the optimal 
conditions of the 
process. 
 

  High pipe 
temperatu
res 

Uncalibrated 
measuring 
instruments 

Failures in the 
piping system 

Check in detail 
the operation of 
each part of the 
steam system 

4 2 M Entities trained to 
maintenance.  have 
personnel experienced 
in the handling of the 
tools 
 

  Delay in 
mixing 

Breakage in the 
feeder mixer. 

Decreases 
capacity and 
product quality 

Repair mixer and 
review 
maintenance plan

 5 2 M Purchase machinery of 
quality. have personnel
experienced in the 
handling of machines 
and the tools. planning 
of maintenance 
programs 

  Pollution Microorganisms 
that interact 
with milk due to 
poor cleaning of
heat exchange 

Loss of the final 
product 

Standardized 
preventive 
maintenance and 
control programs 
for cleaning of 
heat exchanges 
by process 
operators 

5 3 H Establishing a timeline 
with activities and 
responsible people of 
cleaning of each area. 
Creating a program of 
preventive 
maintenance of each 
machine and its 
components 

  High / low 
temperatu
re 

Temperature 
decrease in the 
heat exchange 
due to the 
malfunction of 
the pneumatic 
valves 

customer 
poisoning 

Check and 
calibrate the 
pneumatic valves

5 2 M Checking the 
calibration parameters 
frequently. Creating a 
preventive 
maintenance program, 
with prevalence in the 
critical components

  No 
agitation 

Power supply 
failure, Failure 
in the agitation 
system 

Decreased 
conversion, 
imperfect mixture.

Routine checks of
the agitation 
system, routine 
Maintenance of 
the agitation 
system, 
Installation of an 
emergency 
generator for 
power failure.

5 3 H Having at least two 
sources of electric 
power generation for 
an emergency. 
Creating a program 
with preventive and 
corrective activities 
that permit an 
assertive reaction in an
emergency  

  No flow of 
milk 

Compressor 
failure / 
obstruction, 
valves closed, 
pipe leak 

It paralyzes the 
production 
process. 
Production costs 
increase 

Review periodic 
state of the flow 
of the milk and 
the ducts to 
prevent 
breakdowns, 
obstructions and 
leakage of 
pipelines.

5 3 H Implement a 
comprehensive valve 
system to prevent 
breakdowns, 
obstructions, and 
periodically carry out 
preventive 
maintenance. 

  Reverse 
flow 

Pump failure Production 
stopped 

Constant revision 
of pumps 

5 3 H Perform pump 
maintenance, in 
addition to maintaining 
flow and process 
control 

  Agitation Loss of control Movement of the Preventive 5 4 H Periodic change of the 

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of the speed of 
rotation of the 
motor by 
voltage failure 
and system of 
electrical 
energy 

propellers of the 
agitator 
uncontrolled 

maintenance, 
review periodic 
networks 
electrical plant 

tension pulleys. To 
Acquire an electric 
power plant 

Temperat
ure 

Thermal 
inactivatio
n  

General 
pasteurizer 
failures 

High microbial 
load in the final 
product 

Safety integrity 
level mass flow 
control   

5 4 H Controlling the time 
and temperature and 
to implement a system 
of random sampling 
with microbiological 
tests that guarantee 
the quality levels in the 
pasteurization process.

  Heat 
transfer 

The deviation of
5 °C with 
respect to the 
water outlet of 
the unit hot 
water 

Greater 
resistance to heat
transfer in the 
heat exchanger 
due to fouling in 
the equipment. 
Delay in the 
process.

Requires 
cleaning by 
qualified 
personnel and 
quality inputs. 

5 2 M Planned maintenance 
programs are optimal 
to the periodicity of the 
process 

  Low and 
high 
temperatu
re 

The lack of 
standardization 
and control of 
the 
pasteurization 
process.  In 
which a 
temperature 
must be 
managed of 70 
to 75 °C for a 
period of 10 to 
15 seconds. 

The permanence 
of agents 
pathogens in the 
final product for 
the short period 
of time of 
exposure of the 
milk to the 
temperature, The 
loss 
characteristics of 
the milk as 
nutrients or 
vitamins for a 
long time of 
temperature

Control the 
process by 
means of 
instruments such 
as termometers 
and timers. 
Implementation of
a control that 
opens an air 
valve triple that 
switches when 
the product has 
reached the 
temperature of 
pasteurization 

5 3 H Implement a system of 
indirect heat. 
Controlling and 
document the 
parameters like time 
and ranks of maximum 
and minimum 
temperature in the 
thermal process with 
traceability records 

  No heat 
extraction 
from 
reactors 

Inefficient 
design of 
reactors that 
increase the 
risk of explosion

Explosion    
accidents 

Increased 
monitoring of 
component 
status, 
replacement of 
critical 
components with 
higher reliability 
components,  
Improving reactor 
power                   
Installation of 
protective walls    

5 3 H Maintain a follow-up 
maintenance 
programs. have 
experienced staff in 
the training and 
handling of machinery.

  Cooling 
system      
failure        

Cooling system 
failures 

Fires, explosions Reaction leak 
identification 
software based 
on energy 
balance                

5 3 H Periodic verification of 
the functioning 
machines through 
control charts 

  Critical 
temperatu
re 
threshold 

Emergency 
discharge 
system 
malfunction 

Fires, explosions  Risk prediction 
analysis 

5 5 VH Creating an 
emergency protocol 
with corrective 
measures 

Transfer Transfer 
of heat 

Insufficient 
inhibition of the 
microbial load 

Intoxication of 
customers, and 
total loss of the 

Implement a 
system of 
recirculation of 

5 1 M Standardize and 
document the 
parameters like time 

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due to improper 
heat treatment 

product the milk to 
increase 
inhibition of the 
microbial load   

and ranks of maximum 
and minimum 
temperature in the 
thermal process. 
Delegating responsible 
people in the control of 
critical parameters

4. Conclusions 
The use of HAZOP allows us to conclude that the method is appropriate when identifying the existence of 
risks within the mixing and pasteurization process. The identification of faults in the systems that generate 
alterations and lack of precision, especially in the operational parameters (temperature and pressure), warns 
of the need for measures such as detailed inspections and maintenance. Also, it allows the recognition of the 
repercussions that could be had, such as the deterioration and performance of the machinery, safety risks to 
employees, and the quality of the final product, which could influence consumer satisfaction and well-being.  It 
is noteworthy that many of the risks can mitigate through operational controls such as the anticipation of 
failures of each machine based on evaluation tools such as the documentation of maintenance activities, 
generation of schedules with functions aimed at responsible persons, statistical sampling methods that allow 
evaluating consequences and preventive and corrective measures at different stages. In conclusion, the 
technique allows the increase in safety levels within a process in which it is crucial that the milk meets the 
appropriate microbiological parameters, avoiding situations where the health of consumers can be affected.  

References 

Aouanouk, A., Absi, A., Mouheb, A., Tounsi, Z., 2018, Milk Heat Treatments: Temperature Effect on Fouling, 
Chemical Engineering Transactions, Vol 71, 1267–1272. 

Gonzalez, S.M., 2013, UF1281: Preparation of Milk for Consumption, ProQuest Ebook Central, Madrid, IC 
Editorial.  

IEC, 2016,  IEC 61882 Hazard and Operability Studies(HAZOP Studies)‐Application Guide, Edition 2.0.   
Kunte, V.A., Sakthivel, S., 2016, Useful Tips for a Successful HAZOP Study, Hydrocarbon Processing, 51–57. 
Freedman, P., 2003, HAZOP as a risk analysis methodology, Petrotecnia, Buenos aires, 60-64.  
Marhavilas, P.K., Filippidis, M., Koulinas, G.K., Koulouriotis, D.E., 2019, The integration of HAZOP study with 

risk-matrix and the analytical-hierarchy process for identifying critical control-points and prioritizing risks in 
industry – A case study, Journal of Loss Prevention in the Process Industries, Vol 62, 1–16. 

 

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