Human Factor in Alarm Management

7/27/2019 Human Factor in Alarm Management

1/7

HUMAN FACTORS IN ALARM SYSTEM MANAGEMENT:INFORMATION VERSUS DATA

David A. Strobhar

Beville Engineering, Inc.

201 West Franklin, Suite DDayton, Ohio 45459

ABSTRACT: INFORMATION VERSUS DATA

The design of process plant alarm systems requires that process upset data be translatedinto information for operators and supervisors. Techniques for the translation of data into

useful information are discussed relative to hardwired, CRT-based, and hybrid alarmsystems. The application of human information processing characteristics and human

engineering principles to alarm system design and alarm management is highlighted.

INTRODUCTION:

The purpose of an alarm warning system has remained constant over the past few decades alarms are still present to alert a person to some event or condition. The alerting

function is not one of random or spurious alerting; rather, the alerting is to prompt anaction from the individual, whether it is to inspect a system or use some control.

In contrast to the alarm systems consistency of function, the methods to carry out that

function have changed remarkably. The advent of CRTs/VDTs (Cathode Ray Tubes/Video Display Terminals) and distribution control systems has provided the system

designer with new opportunities and ways to present alarm information. No longer is thedesigner forced to utilize hardwired, single-cause alarm panels.

The change in control systems has also changed the role of the system user, for this

discussion, the process plant operator. Operators have become more of a problem solverand less of a direct controller (1). The operators primary function is to backup the

automatic control system and utilize the superior flexibility of the human informationprocessing system to diagnose complex problems and upsets.

This new type of operator can now be provided alarm data in almost unlimited quantity

and format. Unfortunately, the operator, the problem solver, doesnt need data.

INFORMATION OVER DATA:

Data alone are essentially useless. Given just data, E.G. 291693201, making a decisionwould be difficult. Information is needed to make a decision.

What, then, differentiates information from data? Simply, information is data with

meaning or structure:Information = Data * Structure


2/7

The data 291693201 is meaningless until structure, two hyphens, is added to form 291-69-3201. The structure forces the data to resemble that associated with a social security

number. The information is now that the sequence of digits is most likely a social securitynumber. The structure has not changed the data, but it has provided the person with

information that can be used to make a decision or come to a conclusion.

With regards to an alarm system, and alarm is to prompt an action. An action requires adecision. A decision requires information. The trick then is to ensure that process data is

transformed into alarm information.

HUMAN FACTORS ENGINEERING OF WARNING SYSTEMS

The goal of a well-designed warning system is to prompt the operator to the intendedaction in the required period of time. The need for information being provided the

operator is one necessary criterion, as previously discussed. However, providinginformation is a vague goal and must be achieved by more concrete analytical techniques.

The man-machine model (Figure 1) forms the basis for the creation of alarm systems that

provides information and not just data. Relative to alarm systems, the output of the modelis an action related to the system in which the alarm is activated. The alarm is the input

upon which the operator acts to make a decision on what output is required. This holdstrue for any warning system: hardwired, computer-based, or hybrid.

The driving feature of the man-machine model is the output: What is the desired operator

action. If no action can be defined, no alarm should be provided. Likewise, if the sameaction is the output for two alarms, only one alarm is needed.

The information processing portion of this model is the most difficult to apply, but also

the area of greatest potential gains. Information processing analysis is the definition ofthe structure that will transform data into information. The human information processing

system has several unique characteristics that should be reflected in alarm system design.

The first and perhaps most important characteristic is our limitation to mentally handlepieces of information. Our conscious, or short-term memory is restricted to seven, plus or

minus two, chunks of information (2). Stress, anxiety, and tension lower that numbereven further. Therefore, alarm systems should not present over seven chunks of

information at a time.

The second characteristic provides the caveat for the first; namely, we humans like toprocess information in a holistic manner, combining and aggregating information into

groups or patterns that result in the reduction of the total chunks of information. Usingour previous example, 291-69-3201 would be processed as one chunk, not nine.

These two conflicting and complimentary characteristics are what allow an operator to

look at alarm panels with 300-1,000 annunciator alarms and not be overloaded. Anoperator can combine the alarms in manageable sized groups.


3/7


4/7

A well human engineered system will contain the structure that facilitates the aggressionof alarm data into information groups.

The input aspect of the model is quite simple once the output and transformation pieces

have been defined. The only variables left are the assurances that the alarm is detected

(visibility, conspicuity, signal/ noise ratio) and the message understood (readability,clarity, comprehensibility). Existing human factors engineering standards document therequirements for display parameters (3), (4), (5).

A PRACTICAL EXAMPLE: HYBRID ALARM SYSTEM

Beville Engineering undertook an analysis of a proposed Hybrid Alarm System design.

The system would combine a modern distributed control system with two hardwiredalarm annunciator panels. The unit where this would occur was a fluid catalytic cracking

unit at an older, mid-size U.S. oil refinery.

Two alternative concepts were proposed by the refinery for the two-hardwired alarmpanels: (1) only critical alarms on the two panels or (2) critical alarms on one panel and

non-critical alarms on the other. Either concept is valid and achievable. The task was todetermine the superior concept and to structure the data in either concept, using the man-

machine model, into useful information.

Remember that in distributed control, the operator must search for the part of the processthey wish to inspect. The operator can no longer simply scan the boards looking for

anomalies. In addition, the operator is to solve complex problems and back-up theautomatic control.

The operator output requirements (actions) were delineated through procedural walk-

throughs. Operators were queried regarding how they responded to key process upsets.Included in the walk-throughs were questions regarding the decision process the

operators used to diagnose upset causes. Structure provided to alarm data by the currentcontrol room design was delineated.

It was determined that the first concept proposed by the refinery (i.e., only critical alarms

on the two panels) would be of greatest benefit to the control room staff. The criticalpanel concept would allow the chief operator and other supervisory personnel to obtain

situational status at a glance without having to disturb the board operators. A criticalpanel concept could also provide the operators an overview of the situation and act as a

cheat sheet (direct them on where to look) on which system alarms should be called-upon the CRT screen.

No part of the alarm system (CRT displays, keyboards, alarm panels) is independent of

any other part; therefore, it is essential that the critical panels be configured for ease ofuse with the CRT displays and the computer keyboard. An integrated concept was

developed and shown in Figure 2. The panel columns were dedicated to a system withsub-systems in groups of four in the column.


5/7

Figure 2. Hybrid Alarm System Concept


6/7

Each group of four (sub- system) corresponded to a key on the keyboard in the samerelative location. The key accessed a display showing all alarms for the sub-system.

Many of the critical alarms were logically combined (OR-ed) sub-system alarms,forming a single trouble alarm.

Several other features were utilized as part of the alarm system design. Pump alarms weregrouped with their corresponding flow alarms, as operators indicated that upon a lowflow alarm they first checked the pump alarm to see if the problem was a controller or a

pump. The grouping of alarms into column-systems allowed hierarchal labeling (e.g.,label the column power recovery train, and not repeat this on each alarm titled) for

enhanced readability. Alarm titles were given a standardized nomenclature ofitem/parameter/condition (e.g., vessel/level/high)

The basic approach for the Hybrid System applies to both conventional and advanced

warning systems. That is, seek out the user and define (1) what are they supposed to doand (2) how will they decide to do it. Design of an alarm system to accomplish (1) and

(2) is then relatively straightforward.

CONCLUSION:

The key to the design of an effective alarm system is to ensure that the operator isprovided with information. Data are not information; rather, information is data within a

structure. It is the responsibility of the alarm system designer to provide structure to thedata and ensure that the operator has information.

A four-step process forms the basis for ensuring proper data structure (i.e., information).

The four steps are based on the model of man-machine systems and are:

1) Define the desired action.2) Determine how the decision for action will be made.3) Structure alarm logic to support the decision.4) Design the physical system to transfer the information to the operator.

A well human factored and easy to use alarm system is not difficult to achieve. Simple

incorporation of the job requirements and human information processing characteristicsinto system design produces the desired result. Minimal impact is made on project time

and cost, while a significantly positive impact is made on system efficiency and safety.


7/7

REFERENCES

(1)Eberts, R.A., and Schneider, W., Internalizing the System Dynamics for aSecond Order System. Human Factors, 1985, 27 (4), 371-393.

(2)Miller, G.A., The Magical Number Seven, plus or minus two: Some units on ourcapacity to process information. Psychological Review, 1956, 63, 81-97.(3)McCormick, E.J., Human Factors In Engineering and Design, McGraw-Hill, NY,1976, 4

thedition.

(4)Van Cott, K., and Kinkade, R., (Eds), Human Engineering Guide to EquipmentDesign, U.S. Government Printing Office, 1972.

(5)_______, MIL-STD-1427C, Human Engineering Design Criteria for MilitarySystems, Equipment and Facilities, U.S. Government Printing Office.

Documents

Human Factor in Alarm Management