PAAG procedure

The PAAG procedure describes a systematic procedure for finding possible deviations and malfunctions in systems of all kinds. The method that is identical to the HAZOP procedure (from English Hazard and Operability ) has become established, in particular as an instrument of safety technology in process , Pharmaceutical and petrochemicals. The acronym HAZOP stands for the four steps P rognose (systematic search of possible deviations and disorders), A uffinden the causes (determining the causes within the system under study), A bschätzen the impact (determining the logical consequences of deviation), G egenmaßnahmen ( Evaluation of existing measures and decision on appropriate further countermeasures). The procedure is characteristic of the procedure as a methodical, guided brainstorming session in a group of experts from various fields.

Basics of the PAAG / HAZOP process

Objective of the procedure

The aim of PAAG / HAZOP is to uncover possible deviations from the intended operation of a system, to name the respective causes and effects (and, if necessary, to evaluate them) and to define suitable measures to prevent the scenarios. The central component of the process is the use of so-called key words, by means of which the deviations and faults are "generated".

Key words of the PAAG procedure and their explanation
Motto	Explanation
No or not	The target function is not fulfilled or does not take place
More	Quantitative increase in process variables, something is happening too much
Fewer	Quantitative decrease in process variables, something happens too little
As well ... as	In addition to the normal process, something else happens
Partially	The target function is only partially fulfilled or individual parts of the target function are not completely available
reversal	Something happens in the opposite direction or in the opposite order
Different to	Elements of the target function are replaced by something else

The study is always processed by an interdisciplinary group whose participants come from different specialist areas (in the case of process engineering systems typically from production or process development, measurement and control technology , engineering technology and safety experts). Thus, different viewpoints and experiences can be taken into account. The study is led by a moderator that is as independent as possible; In addition, there is the keeping of the minutes, which can possibly be in personal union with one of the aforementioned roles.

method

A safety assessment according to PAAG / HAZOP usually involves the following four steps:

Forecast of deviations

The first step is to predict possible deviations from the intended operation of the process under consideration. For this purpose, the process or system to be examined is first broken down into manageable “functional units” and the intended operation of each individual functional unit is described in detail as a “target function”.

Example of a target function
Use pump P003 to dose 25 kg of catalyst solution (30%) at 80 ° C into the pressureless container R001 within one hour.

A process can include many dozen or even hundreds of target functions. The time required for the study must be planned accordingly. If necessary, the detailed consideration can be limited to safety-relevant system parts. To predict the deviations, each of these target functions is linked to the key words mentioned.

Examples of the application of the key words to the target function
Motto	Explanation	Examples
NO, NOT	The target function is not fulfilled or does not take place	The catalyst solution is not added.
MORE	Quantitative increase in process variables, something is happening too much	More than 25 kg of catalyst solution are added. The addition takes more than an hour. The addition takes place at a temperature above 80 ° C. Overpressure prevails in the reactor during the addition.
FEWER	Quantitative decrease in process variables, something happens too little	Less than 25 kg of catalyst solution are added. The addition takes less than an hour. The addition takes place at a temperature below 80 ° C. During the addition, there is negative pressure in the reactor.
AS WELL ... AS	In addition to the normal process, something else happens	In addition to the catalyst solution, rust is also introduced (this could mean a stronger catalytic effect). An inhibiting impurity is also entered. In addition to reactor R001, reactor R002 is also filled. The catalyst solution also reaches the environment (due to a leak) in addition to reactor 001.
PARTIALLY	The target function is only partially fulfilled or individual parts of the target function are not completely available	There is no solvent in the catalyst solution. There is no catalyst in the catalyst solution.
REVERSAL	Something happens in the opposite direction or in the opposite order	Catalyst solution is taken from container R001. The catalyst solution is added before or after the other process steps
DIFFERENT TO	Elements of the target function are replaced by something else	Adding another substance instead of the catalyst solution. Adding the catalyst to a different container than R001. Addition in a different way than with dosing pump P003.

Note: the various scenarios are considered individually and independently of one another.

Finding the causes

On the basis of process knowledge and its own experience, the team of experts looks for (organizational and technical) causes that could be the basis of the respective scenario. The basic assumption here is that countermeasures already in place in the system (e.g. overfill prevention devices, safety valves, operating instructions) are initially not taken into account.

Assignment of possible causes to the deviations
deviation	Causes (exemplary)
...	...
more than 25 kg of catalyst solution added	Incorrect quantity specification in the recipe. Incorrect quantity preselection on the counter. Multiple additions due to lack of documentation. No automatic shutdown of the pump.
...	...

In practice, a (semiquantitative) assessment of the probability of occurrence is also often carried out.

Assess the impact

Based on the process knowledge, the team of experts considers or calculates the possible effects that could arise from each scenario. Here, too, existing countermeasures are initially not taken into account.

Assignment of possible effects to the deviations
deviation	Effects (exemplary)
...
more than 25 kg of catalyst solution added	Acceleration of the reaction → Increased heat production that cannot be dissipated by the existing cooling → Rise in temperature in the reaction mass → Reaching the decomposition temperature → Rise in pressure and temperature beyond the design limits of the reactor → Container failure with leakage of harmful product and flammable solvent → Health risk for employees and Third party and risk of explosion.
...

In practice, a (semiquantitative) assessment of the extent of damage is also often carried out.

Countermeasures

For the identified security-relevant scenarios, the team of experts determines measures to prevent occurrence and, if necessary, to limit damage, based on the findings and technical feasibility. Reference can now be made to existing facilities and instructions, provided that these are considered effective and sufficient for the damage processes discussed. The required reliability (effectiveness) of the measures to be taken will be based on the severity of the effects and the likelihood that the causes will take effect.

documentation

The PAAG / HAZOP study is usually documented in tabular forms, either using standard office software or using commercial programs. Columns are typically created for numbering, deviations, causes, effects, evaluation, measures and comments. Some companies differentiate more so that there are also forms with 30 or more columns. The different scenarios are then documented in the lines.

Example of a table for documentation
number	deviation	causes	Effects	rating	activities	classification	Remarks

Modifications and extensions of the PAAG / HAZOP process

Modifications

In many companies, the classic key words are "translated" into specific questions for practical application by defining possible deviations from the combination of key words and process parameters.

Specification of the key words
Motto parameter	No	More	Fewer	reversal	different from / both and / partially
material					Wrong substance / contaminated substance
Quantity or volume flow	no	too much	too little
temperature		too high	too low
pressure		too high	too low
Period or duration		too long	too short
time				Wrong order	Wrong time
Place or way				Wrong direction	Wrong location / leak
reaction	no	too fierce	too sluggish	Decomposition instead of synthesis	Wrong reaction / side reaction / incomplete reaction
Auxiliary energies	failure	too little	too much	Product in auxiliary media system	Wrong media / contaminated media
...

The indicated combinations of key words and parameters are then taken directly as deviations for the start of the discussion. Depending on the company, differently differentiated and thus differently extensive questionnaires are used. A completeness of the consideration does not result from the number of aspects (a large number can even be counterproductive for the discussion in the team), but from the experience and routine of the moderator.

In some companies there are also opposing approaches: the restriction to four key words (no, more, less, different than), which are used to steer the discussion. In this case, too, the moderator's experience and routine are decisive for the success of the study.

Extensions

The PAAG / HAZOP procedure is originally used to develop and describe scenarios for deviations and faults. In practice, the PAAG procedure is therefore usually linked with risk assessment methods (e.g. ZHA, FMEA , LOPA, risk graph ) and used as an instrument for hazard identification, since these methods are not preceded by such a comprehensive search for scenarios. It is therefore the combination of methods that characterizes the quality of a safety assessment.

History of the PAAG / HAZOP process

The beginnings at ICI

As the British company ICI in the early 1960s was planning systems for a new generation of pesticides to build, it was faced with the challenge of highly toxic intermediates having to master and dangerous process steps. It was therefore decided to develop a fundamentally new method for checking the plant and process design. The departments involved in the planning should not only look at the trade they are responsible for, but should also jointly take a look at possible deviations from the intended process, find the corresponding causes and describe the potential effects. “Critical Examination” was the name given to this procedure, in which every single process parameter of the procedure was questioned using “guide words”.

Two experiences were made with this approach: firstly, that this methodology uncovered a whole series of planning errors that had not been found with the usual routine. Second, that this approach was successful, but also extremely time-consuming and therefore could not be applied to all new plans.

The method was improved in 1967 in the ICI's petrochemical division. The “Guide Words”, which had previously been limited to the purely verbal process description, was now used in combination with the P&ID schemes (piping and instrumentation flow diagrams) of the process. And the documentation was limited to necessary changes or open questions. This “flowsheet method” accelerated the process by a factor of ten and resulted in HAZOP studies now being routinely used in a wide variety of plant types.

In 1970 the Pharmaceutical Division of ICI took over the HAZOP process. The “study leader”, who managed the systematic investigation, and the support of a technical secretary, who recorded the results in tabular form, were introduced. This guided the discussion and encouraged the team's creativity, so that this division of roles was perceived as a significant improvement. At the same time, the procedure was also applied to batch processes for the first time and manual activities of the operating personnel were included.

With these organizational changes, the methodology achieved its breakthrough. On the basis of the modifications, ICI began to carry out training courses in 1975 in order to be able to check all existing and new systems with the method for safety. The ICI internal report on "Hazard and Operability Studies" was published in 1977 by the Chemical Industry Association. At the same time, seminars were offered to train the practical application of the process. Chemetics International Company, the Canadian branch of the ICI's engineering department, translated the brochure into numerous languages and provided appropriate training to spread the method worldwide.

HAZOP becomes PAAG in German-speaking countries

In March 1980, the Chemistry Section of the International Social Security Association (ISSA) published the first German-language brochure on the PAAG process. The booklet was the literal translation of the 1977 HAZOP brochure "A Guide to Hazard and Operability Studies" by the British Chemical Industries Association and had the sensational title "The Incident in Chemical Operations". In May 1980, the Chemicals Employers' Liability Insurance Association (now BG RCI) organized the first training event on the method under the leadership of ICI experts. The majority of the participants in the seminar came from well-known companies in the large-scale German chemical industry and plant engineering, but from the outset numerous representatives of the authorities were also interested in attending the seminar. A few days after the event, on June 27, 1980, the federal government passed the 12th ordinance for the implementation of the Federal Immission Control Act - the Major Accidents Ordinance, from which the so-called Seveso Directive emerged two years later at European level. According to this, the relevant companies were required to provide evidence in the context of a safety analysis that “a public risk as a result of a disruption in normal operation” could be excluded. And when, on April 27, 1982, the Second General Administrative Regulation for the Hazardous Incident Ordinance (2nd StörfallVwV) explicitly listed the PAAG procedure as one of the methods to meet the requirement for a systematic approach, the procedure was widely accepted.

The brochure is regularly updated and updated by the Chemistry Section of the International Social Security Association (ISSA).

Further development of PAAG and HAZOP in the process industry

From the 1990s onwards, the measurement, control and regulation technology equipment used in companies in the chemical industry was also increasingly used to control process deviations in the interests of system security. The Riskograph was developed by the standards working group for measurement and control technology in the chemical industry (NAMUR, since 2005 interest group for automation technology of the process industry eV), which enabled the classification of the so-called protective devices, the availability of which went beyond that of the operating and monitoring devices. In the Anglo-Saxon countries in particular, the risk matrix approach came up around the same time , which also made it possible to assess the potential danger posed by process plants. Both approaches often use the PAAG / HAZOP procedure to find critical scenarios.

In addition to HAZOP, the HAZID method for upstream hazard identification was created to enable an assessment of the extent to which risks are to be expected and to adjust the depth of HAZOP accordingly, and the HAZAN tool for hazard analysis to meet requirements adapt the protection concept. A corresponding brochure from Trevor Kletz explains the procedure. Similar instruments were developed in Germany to supplement the PAAG, with company-specific solutions being the rule. Practical experience with the HAZOP methodology was collected by industrial colleagues in a paper from the European Process Safety Center (EPSC), which shows that some of the original ideas, such as applying all key words to all elements of the target function, do not improve quality, but do bloated discussion and documentation meant.

Much has also happened in the use of the PAAG process and the combination of PAAG as a method of hazard identification with the evaluating instruments risk matrix, risk graph, FMEA (failure modes and effects analysis) or LOPA (layers of protection analysis) are commonplace today would be.

literature

IEC 61882. Hazard and operability studies (HAZOP studies) - Application guide. 2001, International Electrotechnical Commission (IEC), Geneva.

Individual evidence

↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k Joachim Sommer et al .: The PAAG process - methodology, application, examples . Ed .: IVSS Chemistry Section. 4th edition. Heidelberg 2008, ISBN 92-843-7037-X ( bgrci.de ).
^ Knowlton, Ellis: A Guide to Hazard and Operability Studies . Ed .: Chemical Industries Association. 1977.
↑ Federal Law Gazette 1980 Part I, p. 772 ff (Ed.): Störfallverordnung .
↑ GMBl. 1982, p. 203 ff (Ed.): Second general administrative regulation for the Hazardous Incident Ordinance .
↑ Kletz, Trevor: Hazop and Hazan . 4th edition. Taylor & Francis, 1999, ISBN 0-85295-421-2 .
↑ European Process Safety Center (Ed.): HAZOP: Guide to Best Practice . 2nd Edition. 2008, ISBN 978-0-85295-525-3 .
↑ IVSS Chemistry Section: Hazard identification and assessment in plant safety . Ed .: IVSS Chemistry Section. 2nd Edition. Heidelberg 2012, ISBN 92-843-7122-8 .

[Joachim_Sommer-1] ↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k Joachim Sommer et al .: The PAAG process - methodology, application, examples . Ed .: IVSS Chemistry Section. 4th edition. Heidelberg 2008, ISBN 92-843-7037-X ( bgrci.de ).

[2] Knowlton, Ellis: A Guide to Hazard and Operability Studies . Ed .: Chemical Industries Association. 1977.

[3] Federal Law Gazette 1980 Part I, p. 772 ff (Ed.): Störfallverordnung .

[4] GMBl. 1982, p. 203 ff (Ed.): Second general administrative regulation for the Hazardous Incident Ordinance .

[5] Kletz, Trevor: Hazop and Hazan . 4th edition. Taylor & Francis, 1999, ISBN 0-85295-421-2 .

[6] European Process Safety Center (Ed.): HAZOP: Guide to Best Practice . 2nd Edition. 2008, ISBN 978-0-85295-525-3 .

[7] IVSS Chemistry Section: Hazard identification and assessment in plant safety . Ed .: IVSS Chemistry Section. 2nd Edition. Heidelberg 2012, ISBN 92-843-7122-8 .