Suva Exemplu Metoda-e Brici

Risk of an injury caused by a saw blade without any safety measures

Risk of an injury caused by a saw blade with safety measures

R1

R2

The Suva method for the risk assessment of technical devices and equipment

Working safely

This publication has been issued for use by the manufacturers and other suppliers of machinery. It describes a method of risk analysis and risk assessment for technical devices and equipment and contains specific assistance for the compilation of a technical documentation in accordance with Machinery Directive 98/37/EC.

Suva Swiss national accident insurance fund Occupational safety P. O. Box, CH-6002 Lucerne Telephone 041 419 51 11 Fax 041 419 59 17 (for orders) Website: www.suva.ch The Suva method for the risk assessment of technical devices and equipment Authors: Mauritius Bollier, Fritz Meyer, Technology section (ALT) Reproduction stating source permitted. 1st issued – July 1990 Revised – July 2002 16th edition – July 2002 Order number: 66037.e

Table of contents

1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

2

Overview of the procedure . . . . . . . . . . . . . . . . . . . . . . . . . .

5

3

Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6

4

How does an incident occur? . . . . . . . . . . . . . . . . . . . . . . . .

7

5

The causes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8

6

An example based on a circular saw . . . . . . . . . . . . . . . . . .

9

7

Description of the data used in risk assessment and risk reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10

8

Determining the limits of a machine . . . . . . . . . . . . . . . . . . . 8.1 Limits of a machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 Listing and describing the life-cycle and operating modes of a machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3 Determining where the machine is to be used . . . . . . . . . 8.4 Identifying the persons involved . . . . . . . . . . . . . . . . . . . .

11 12 12

Identifying danger situations . . . . . . . . . . 9.1 Establishing dangers . . . . . . . . . . . . . . 9.2 Listing danger situations . . . . . . . . . . . 9.3 Investigating incidents and their causes

. . . .

16 16 18 18

10 What does «risk» mean? . . . . . . . . . . . . . . . . . . . . . . . . . . . .

21

11 Risk estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

22

12 Risk 12.1 12.2 12.3

. . . .

24 24 24 26

13 Risk reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.1 Choice of safety measures . . . . . . . . . . . . . . . . . . . . . . . 13.2 Assessment of the safety measures . . . . . . . . . . . . . . . .

27 27 29

14 Contents of the technical documentation . . . . . . . . . . . . . . 14.1 Description of the solutions . . . . . . . . . . . . . . . . . . . . . . .

30 30

15 Further information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

34

9

evaluation . . . . . . . . . . . . . . Formulating safety objectives Determining an accepted risk Risk classification . . . . . . . . .

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3

1 Introduction

In accordance with the Federal Law on the safety of technical devices and equipment (STEG), Article 3, the following requirements apply to the manufacturing or introducing of technical devices and equipment: When used appropriately and with care, such technical devices and equipment must not endanger the life and/or health of users and third parties and they must fulfil the essential health and safety requirements. If no essential health and safety requirements have been specified, they must have been produced according to recognized technical principles. For machinery, the essential health and safety requirements according to Annex I of Machinery Directive 98/37/EC (formerly 89/392/EEC) will apply. The third preliminary observation to Annex I of the Machinery Directive states that: «The manufacturer is under an obligation to assess the hazards in order to identify all of those which apply to his machine; he must then design and construct it taking account of his assessment.» The Machinery Directive also requires that measures must be taken to avoid the risk of accidents associated with the machine. To demonstrate that the technical device or the equipment satisfies all essential health and safety requirements, the person(s) manufacturing or importing the machine must provide a technical documentation.

4

This documentation must also include a description of the solutions that have been selected to eliminate or limit the risks inherent in the use of the machine. This publication will show you how to carry out the risk assessment systematically. The procedure described is based on the procedural steps that are given in EN 1050 «Safety of machinery – principles for risk assessment». This is concluded by a description of the data that can be used for the technical documentation. The completeness of a risk assessment is decisive for its quality. A result that is as complete as possible can only be achieved by means of cooperation between different experts who are familiar with the product. For example, cooperation between persons from the fields of design, installation, purchasing, sales, occupational safety is desirable. Users should also be included in the risk assessment.

2 Overview of the procedure

Risk analysis

Determining the limits of a machine

Risk assessment

Identifying hazardous situations

Risk estimation

Risk evaluation

Is the machine safe?

NO

YES

Definition of intended use in the operating instructions. Description of the safety measures selected to prevent any risks arising from the use of the machine and information on residual risks. A description of residual risks for which no safety measures are necessary is also recommended.

Technical documentation

Select safety measure

Risk reduction

No further safety measures necessary

Fig. 1: Overview of the procedure for risk assessment and risk reduction.

5

3 Terminology

Danger:

Origin of an injurious action. Depending on its current effect, the danger can be active or latent.

Active danger

Danger zone:

Latent danger

The zone in which an injurious action will spread. Danger zone

Danger situation:

A situation in which a person is close to a danger. There are three types of danger situations: A person next to a latent danger

A person in the area of a latent danger

A person next to an active danger

Hazard:

A danger situation in which a person is in the area of a latent danger.

Causes:

Influences that can change a danger situation and lead to an incident. The causes change the position of the person with regard to the danger zone and/or the activity of the danger.

Incident:

An incident takes place when a person is exposed to an injurious effect.

6

4 How does an incident occur?

The co-incidence of an injurious effect and a person is a prerequisite for an incident happening. An injurious action

affects

a person

=

an incident







Prerequisite The injurious action originates from an active danger. A danger situation arises when a danger and a person are in close proximity to each other. In these situations, the prerequisite for an incident is incomplete. Causes can change these situations in such a manner that a person finds him-/herself in the danger zone of an active danger. The person is then exposed to an injurious action that results in an incident.

Danger (active or latent)

Person

Co-incidence

Prerequisite

Cause

Danger situation

Person enters the danger zone

Ca u

se

Danger becomes active







or

or

Cause Danger becomes active

u Ca

se

Person enters the danger zone

Incident

Fig. 2: How an incident occurs.

7

5 The causes

Two types of cause can occur: N A change in the activity of the danger

(e.g. a machine can start up unexpectedly) N A change in the position of the person

in relation to the danger (e.g. the person enters the danger zone of a rotating saw blade).

Dangers are created when a designer designs a machine. The designer must make sure that, with any inherent danger situations of the machine, the probability of an incident occurring is kept to a minimum. Any conceivable residual incidents must be prevented by instructing the persons who might be involved in a danger situation. All causes that can lead to an incident are therefore dependent on a person's ability, knowledge and intentions.

Causes Incomplete or wrong application Faulty product properties instructions

Careless use of product or non-compliance with instructions

Design

Production

User

Disposal specialist

– inability

Over-estimation of one’s abilities, pressure of time . . .

Lack of experience in manufacturing and installation, . . .

Physical size, concentration, reflexes, . . .

Inadequate equipment, . . .

– ignorance

Lack of training, unforeseeable situations, . . .

Lack of material skills, . . .

Lack of product information, . . .

Lack of product information, . . .

– unwillingness

Cost-cutting, . . .

Cost-cutting, . . .

Ignoring application instructions, absence of a safety culture

Convenience

Product life cycle

Development

Manufacture

Use

Disposal

Responsibility Human qualities:

Fig. 3: Overview of causes.

8

6 An example based on a circular saw

The following example again demonstrates these inter-relations. A machine operator (person) is working with a circular cut-off saw (danger: e.g. the kinetic energy and teeth of the saw blade). Whenever the machine operator is close to the saw blade, a danger situation is created.

Danger

If the machine operator touches the teeth of the rotating saw blade when moving the section to be cut off, an incident will occur (personal injury). Possible cause: The designer did not provide for an adequate guard.

Co-incidence

Person

Prerequisite The saw blade in the machine

Machine operator

or

The machine operator reaches into the danger zone of the saw blade.

Danger situation

The saw is started.

Cause The machine operator is in the danger zone of the nonrotating saw blade.

Ca u







or

Cause The machine operator is next to the danger zone of the non-rotating saw blade.

The machine operator is next to the danger zone of the rotating saw blade.

u Ca

se

se

Incident The saw is started.

The machine operator is in the danger zone of the rotating saw blade: The person is injured.

The machine operator reaches into the danger zone of the rotating saw blade.

Fig. 4: How an incident arises, an example based on a circular saw.

9

7 Description of the data used in risk assessment and risk reduction

The tables on pages 32 and 33 are recommended (templates for copying) as they will help you to follow the individual steps involved in risk assessment and risk reduction. The information collected is then easy to follow. It may be useful to produce and complete the tables on an EDP system.

10

8 Determining the limits of a machine

To enable a risk assessment to be carried out, all the foreseeable danger situations must be identified in connection with the intended use of the product. 8.1 Limits of a machine Limitations of use The intended use of the machine is described first. «Intended use» is the use for which the machine has been built. Any reasonably foreseeable misuse must therefore also be taken into account. Attention must be paid to: – Any foreseeable incorrect action arising from normal inattention – Any reflexes in the event of a malfunction – Any unsafe action as users take the «path of least resistance» – Any use of the machine in a non-professional field (in this case, no technical skills can be presumed) Intentional misuse of the machine is not taken into account. Space limits Limit the system, establish subsystems: The scope of the system to be assessed is clearly set out on drawings or in descriptions. The limits must be set in such a manner that the machine to be assessed is covered completely (inc. cable and plug, etc.) and that an assessment is truly practicable. Extensive systems must be split up into clearly separate subsystems to enable either sub-assemblies, functional units, individual parts or components to be examined. Indicate any interfaces: Following this limitation procedure, the interfaces with other systems must be shown and described. Interfaces arise, for

example, with buildings, other technical systems, energy providers as well as with the environment. The interfaces with the adjacent subsystem must be shown for each subsystem created. As subsystems influence each other, the necessary conclusions must be drawn. Time limits The working life of the entire machine or – if necessary – of parts of the machine (tools, wear-out parts, electrical components, etc.) is laid down with due regard for intended use. 8.2 Listing and describing the life-cycle and operating modes of a machine Article 3 of the Federal Law on the safety of technical devices and equipment requires that the lives and health of users and third parties must not be endangered given appropriate and careful use. All operating modes that are necessary for intended use must be described. Attention must be paid to the full life-cycle of the machine from its construction to its final disposal. This description of the operating modes can also be subsequently used for the formulation of the operating instructions. Normal operation Normal operation is the operating mode in which the system fulfils the purpose for which it is intended and for which it has been built (for example, the normal operation of a circular saw: the cutting off of profiles). Fig. 5: Normal operation of a circular saw.

11

Special operation

Third parties

All operating modes required to ensure normal operation are allocated to special operation.

Third parties are persons who are only indirectly connected with the system. For example, they can be other members of the workforce, visitors or persons who are present by chance.

For example: – Installation – Transport – Test runs – Clearing production faults – Clearing machine faults – Maintenance – Dismantling – Disposal This list is not conclusive. However, the designer is in a position to lay down precisely the special operating modes of his machine. 8.3 Determining where the machine is to be used The areas of use (e.g. industry, trade, household) in which the machine is expected to be used must be stated. 8.4 Identifying the persons involved Persons involved in normal operation In normal operation, the persons affected are those who work on the machine when it is being used appropriately. These are the users and the operators. Persons involved in special operation In the case of special operation, all those persons who ensure that the system can fulfil its intended purpose are affected by the system. These are the persons who are responsible for the various jobs occurring in special operation (e. g. maintenance personnel).

12

The limits of the machine based on a circular saw are described in table 1 on page 13 and in Fig. 6 on page 14. The individual working steps in the operating modes are described in the second column of table 2 on page 15.

Risk assessment: Determining the limits of a machine Machine: circular saw Intended use, limitations of use: – Sawing of a clamped profile with a rotating saw blade – Resetting, retightening the profile and advancing the saw blade are done manually – Cutting maximum profiles of 80 x 100 mm in mild steels, non-ferrous metals and synthetic materials Space limits: Systems as well as the Influences that exceed the system limitations are marked on the drawings SN0. Time limits: Operating life of the machine: Consumables: – Tungsten-carbide saw blade – HSS saw blade – Drive belt Live-cycle, operating modes:

20 years Operating life: 60 hours (depending on the materials being cut) 25 hours (depending on the materials being cut) 5 years

The persons involved User*

Third parties

Machine operator

Electrician

Construction

X

X

X

Transport

X

X

X

X

X

Normal operation

X

X

Production fault

X

X

Machine fault

X

X

Cleaning

X

X

Maintenance

X

X

X

X

Commissioning

Trasport operative

Disposal specialist

.......

X

X

Use

X

................... Decommissioning

X

Disposal

X

X

................... * Training the user: no training presumed

Area of use: Date:

15.02.00

Trade, industry in interior locations with 10 amps power supply and a voltage of 400 volts

Visto: ay

Page:

1 of 1

Table 1: Determining the limits of a machine based on a circular saw.

X

13

Subsystem: «Lighting» Lig h

ht

Lig

t

No ise

ve Le ge a r

ion

rat

Subsystem: «Cutting head»

Vib

er ow

Noi

se

iate

Ch

ips

P

dh

eat

Effort when resetting the profile

Cuttin force g

Subsystem: «Profile»

Chips Clamping force

Clamping force

Hinge ase

Clamping force

Rele

Gravity

Clamping moment

rce

se fo

Relea

Pow adv er of anc e

Rad

ly

pp

su

e

forc

Clamping moment

Subsystem: «Machine operator»

Bearing force

Subsystem: «Clamping device with stand»

Chips

System: «Machine operator using a circular saw in a workshop» Subsystem: «Floor»

Bearing force

Bearing force

Bearing force

Designation: Circular saw Drawing number: SN0

Fig. 6: System and interfaces based on a circular saw.

14

Risk assessment

Machine: circular saw

Operating mode: Normal operation

Subsystem: . . . . . . . . . . . . . . . . . . .

No.

Description of operating mode

1.

Placing the profiles in the vice

2.

Positioning the profile

3.

Clamping the profile

4.

Starting the saw

5.

Lowering the saw blade

6.

Making the cut

7.

Raising the saw blade

8.

Switching of the saw

9.

Removing the sawn-off piece

10.

Releasing the profile

11.

Removing the profile from the vice

12.

Cleaning the vice

Severity of harm (S)

Probability (P)

I II III IV V

A B C D E

Death Severe, permanent injury to health Slight, permanent injury to health Curable injury with incapacity to work Curable injury without incapacity to work

Danger situation

No.

Danger

Person in/ danger zone

Risk No.

Cause

Table 2: Description of normal operation based on a circular saw.

Incident S

P

Safety objective

frequent occasional infrequent improbable almost impossible

No. Measures

Page 1 of ......... Signature: ay Date: 15.02.00 Residual risk S

P

Information

15

9 Identifying danger situations

9.1 Establishing dangers All the danger that can occur in connection with the intended use of the machine within the individual subsystems and on the interfaces between the systems must be identified and documented. In addition, the dangers that can appear owing to a foreseeable, anticipated use of the machine based on reasonable considerations must also be identified. Particular attention must be paid to the following points when looking for dangers: N Each danger can have an injurious effect. N The injurious effect spreads in the danger

zone. N The injurious effect can either be per-

manent or temporary, e.g. unexpected start-up.

Example of dangers in connection with machinery 1. Danger caused by the machine – Crushing – Shearing – Cutting, severing – Entangling – Drawing in, trapping – Impact – Stabbing, puncture – Friction, abrasion – High pressure fluid injection or ejection 2. Danger caused by electricity – Contact of persons with live parts – Contact of persons with parts which have become live under faulty conditions

The following list contains a selection of possible dangers. It must be supplemented according to the product. Further information regarding dangers can be found in EN 1050, Annex A.

– Approach to live parts under high voltage – Electrostatic phenomena – Effects from short circuits 3. Danger caused by thermal energy – Touching extremely cold or hot solid materials, fluids or gases – Fire, explosions, radiation from heat sources – Cold or hot working environment 4. Danger caused by noise – Effect on the hearing and balance, awareness – Effect on speech communication, perception of acoustic signals 5. Danger caused by vibrations – Effects on nerves and vessels (in the case of hand-held tools)

16

– Effects on the whole body (vibration felt by the whole body, particularly when combined with poor postures) 6. Danger caused by radiation – Radiation with low frequency, radio frequency, microwaves – Infrared, visible and ultraviolet light – X-rays and gamma rays – Alpha rays, beta rays, electron or ion beams, neutrons

10. Danger caused by unexpected start-up 11. Danger caused by the impossibility of stopping the machine under the best-possible condition 12. Danger caused by changes in the rotational speed of tools 13. Danger caused by a power failure 14. Danger caused by control circuit failures

– Lasers 15. Danger caused by faulty fitting 7. Danger caused by materials and substances – Contact with harmful fluids – Inhalation of harmful gases, mists, fumes and dusts – Fire and explosions – Contact with biological or microbiological materials (viral or bacterial) 8. Danger caused by the neglect of ergonomic principles in machinery design

16. Danger caused by break-up during operation 17. Danger caused by falling or ejected objects or fluids 18. Danger caused by a loss of stability/overturning 19. Danger caused by slipping, tripping, falling 20. Dangers in connection with special types of machinery

– Unhealthy postures, excessive efforts – Inadequate consideration of human anatomy – Neglected use of personal protection equipment – Inadequate local lighting – Mental overload and underload, stress

9.2 Listing danger situations The possible danger situations are identified by investigating whether an existing danger can possibly have a negative effect on a person. Danger and person are entered under a number in the table.

– Human error, human behaviour – Inadequate design, location or identification of manual controls – Inadequate design or location of visual display units 9. Danger caused by a combination of different dangers

17

Dangers in normal operation:

6

1 Danger of cuts resulting from a rotating saw blade

4

2 Danger of cuts resulting from the teeth of the saw blade 3 Danger caused by stabbing by the saw blade during operation following break-up 4 Danger caused by the saw head falling

1

7

3 2

5

Danger caused by crushing at the hinge

6

Danger caused by vibrations

7

Danger caused by electricity

8

........

5 Designation: Saw head subsystem Drawing number: SN1

Fig. 7: "Sawing head" subsystem in normal operation: risks during normal operation (selection).

9.3 Investigating incidents and their causes The causes can be determined by investigating how a danger situation must change so that a person enters the danger zone of an active danger. The incidents can be estimated together with the causes found. These approaches must be followed for all systems and their interfaces in all operating modes. The following listing shows some examples of causes.

Inability: N Physical size N Handicap N Design faults N Unfavourable ergonomics N Pressure of time N Over-estimation of one's abilities N Lack of understanding

Ignorance: N Poor information N Lack of experience N Incomplete operating instructions

Unwillingness: N Convenience, path of least resistance N Lack of reason N Economy

An example of how to identify a possible incident with the relevant cause is given in table 3.

18

Risk assessment

Machine: circular saw

Operating mode: Normal operation

Subsystem: . . . . . . . . . . . . . . . . . . .

No.

1.

Description of the operating mode Place profile on support

Severity of harm (S)

Probability (P)

I II III IV V

A B C D E

Death Severe, permanent injury to health Slight, permanent injury to health Curable injury with incapacity to work Curable injury without incapacity to work

Danger situation

No.

1.1

Danger

Cutting with the rotating saw blade

Risk

Person in danger zone

No.

Hand or arm of the operator in the area of the saw blade

1.1.1

Unexpected start-up after a power failure and operator’s clothing is trapped by the saw blade

Handand/or arm injury

1.1.2

Unexpected start-up after a power failure when machine operator is correcting the position of the profile

Handand/or arm injury

Table 3: Establishing incidents based on a circular saw.

Cause

Incident S

P

Safety objective

frequent occasional infrequent improbable almost impossible

No.

Measures

Page 1 of ......... Signature: ab Date: 15.02.00 Residual risk S

P

Information

19

Procedure for finding causes If, in a given danger situation, the incident is known or if an incident can be presumed, a «fault tree» is a possible procedure to follow when investigating the individual changes in the danger situation step by step until the origin, the actual cause, has been found.

The use of the fault tree is shown in detail in Suva brochure 66025.e «Sample risk assessment for technical devices and equipment».

Injury caused by a rotating saw blade

and Machine operators in the danger zone of the saw blade

Saw blade rotates

or

or

Being started by a second person who has no overview of the danger zone from the point of starting

Unexpected start-up

Œ

Machine operator is correcting the position of the profile



After the saw blade has jammed in the profile



The saw is being started



Fig. 8: Fault tree for the incident "User is injured by a rotating saw blade".

20

‘

Machine operator intends to remove the cut piece Cut piece jams between the profile and the stop

’

Ž

or

After a power failure

Machine operator’s clothing is entangled by the saw blade

10 What does «risk» mean?

An incident can arise from any specific danger situation with a certain degree of probability. The risk of a dangerous situation is dependent on the severity of the possible harm caused by the incident and by the probability of occurrence The probability of occurrence is determined by the following factors: – The frequency and duration of the danger situation that precedes the incident

For example: a circular saw Risk of a danger situation: a machine operator and a rotating saw blade The

Fig. 9: A person operating a circular saw.

risk when working with the saw blade is dependent on

– The probability of the incident occurring if the danger situation is present

the severity of an injury by the saw blade

– The possibilities for avoiding or limiting the harm

and on the probability of occurrence, i.e. the probability of an injury The probability of it occurring is determined by the following factors: – Exposure time, i.e. how frequently and how long the machine operator works with the saw each time – The probability that the machine operator is injured by the saw blade while working with the saw – The possibility of limiting the harm, e. g. by withdrawing a hand quickly

21

11 Risk estimation

The maximum harm possible and the probability of this harm are estimated for each risk situation. The following diagram can be used to depict the risk:

Severity of harm Based on the injury or the effect on personal health of the persons concerned, the severity of harm can, for example, be allocated to the following categories: I

Matrix representation of a risk

Death

II Serious, permanent injury, fails to heal completely (irreversible), quality of life substantially reduced

Probability of occurrence

At any time

III Slight, permanent injury to health, fails to heal completely (irreversible), quality of life is only slightly reduced IV Curable injury with incapacity to work (reversible)

Risk X

Probability of occurrence X

V Slight injury without incapacity to work (reversible)

In

cr ea

si

ng

ris

k

Probability of occurrence

Severity of harm

Never No injury

Severity of harm X

Fig. 10: Matrix representation of a risk.

Most serious injury

The probability of occurrence is dependent on the specific risk situation. Existing accident data based on statistics can only be used if the risk situation preceding the accident is always the same. For this reason, the probability of occurrence is usually evaluated qualitatively. For example, its probability can be recorded in the following categories: A frequent B occasional C infrequent D improbable E almost impossible

22

If the probability of occurrence is still unclear during the drafting phase of a product, a fairly high degree of probability should be set. The values can be corrected on receipt of subsequent, more precise information. For example: Working with a circular saw The risk of an injury to the machine operator caused by the saw blade. N Maximum severity of harm: Slight, perma-

nent injury to health (injury to finger(s) or hand) N Probability of occurrence: Based on the

causes, (machine operator inserts his/ her hand in the danger zone of the saw blade, saw blade starts up), the probability of occurrence is assessed as being «occasional». Probability of occurrence

A

frequent

B

occasional

C

infrequent

D

improbable

E

almost impossible

Risk of a danger situation: «machine operator and rotating saw blade»

V Curable injury without incapacity to work (reversible)

IV Curable injury with incapacity to work (reversible)

III Slight, permanent injury to health (irreversible)

II

I

Severe, Death permanent injury to health (irreversible)

Fig. 11: Representation of risk based on a circular saw.

23

12 Risk evaluation

The Machinery Directive basically requires that the essential health and safety requirements formulated in Annex I be fulfilled. These requirements are formulated partly as safety objectives and partly as specific demands. 12.1 Formulating safety objectives If the requirements cannot be met owing to the given state-of-the-art technology, the machine must be designed and built in line with the basic safety and health requirements as far as possible. A safety objective must be established for each result obtained. Formulating safety objectives describes the conditions that the solutions must fulfil in order to prevent any occurrence of the possible incidents. A neutral formulation of safety objectives that is wide in scope permits a larger selection of solutions. For the «circular saw» example given in this brochure, one of the safety objectives might be worded as follows: Manual access to the danger zone of the rotating saw blade must not be possible. A more generally worded formulation might read as follows: It must not be possible for anyone to be injured by the saw blade. The difference between the two formulations becomes clear when solutions are required.

24

The safety objective first noted can be fulfilled if the saw is switched off when access to the danger zone is necessary. In the case of the second safety objective formulation, access by the user to the saw blade cannot be possible even when the machine has been stopped, which necessitates a safety guard over the saw blade. It often makes sense to prevent several incidents with one safety objective. When the safety objectives have been formulated for all incidents, safety objectives with the same statement can be summarized. However, nothing important should be omitted when doing so. This is particularly important for safety objectives relating to special operation. When the solutions are being formulated, it can be seen whether several safety objectives can be fulfilled by one solution. 12.2 Determining an accepted risk Each machine will represent a certain risk or residual risk even after the best-possible solution at the time has been taken into account. It is the task of the designer to confine the residual risk to an acceptable degree. For this reason, it is important to reflect on the acceptable risk. The judgment on whether a risk is acceptable or not is influenced by numerous factors (see Fig 12).

Accepted risk

Accepted risk

Major

Accepted risk

Accepted risk Accepted risk Accepted risk

Accepted risk

Minor

Degree of self-determination

Working environment

Minor degree of self-determination:

Major degree of self-determination:

Clerical professions:

Construction industry:

Railway users are unwilling to accept injuries resulting from mistakes made by the railway company.

Hang-glider pilots accept that they can crash owing to errors they make.

Clerical workers are unwilling to accept almost any injuries resulting from their professional activities.

Workers in the construction industry accept minor, reversible injuries that occur despite their adhering to safety measures.

Fig. 12: Risk factors.

Degree of voluntariness At work:

At leisure:

Persons generally have to work and are in a situation of dependence while they work. They would therefore like to carry out their activities without their personal health being affected.

In the case of voluntary activities, substantial risks are accepted to some degree.

Cause Cause independent Cause dependent on the user: of the user (faulty product properA blow on the finties): ger is accepted when hammering in Lift users will not accept any injuries, a nail. e.g. owing to a cable breaking.

Influences on acceptable risks

A selection of factors that influence the acceptance of risks

Risk acceptance

Accepted risk

25

12.3 Risk classification

In the field of machinery, the following influential factors can be of particular importance: N Degree of voluntariness:

The persons who work with a machine must earn their living and are in a situation of dependence while at work. They therefore expect to be able to carry out their professional activities without any professional injury to their health. N Cause:

An injury resulting from a faulty product is neither accepted by law (Federal law on the safety of technical devices and equipment, the Machinery Directive, product liability law) nor is it accepted by society. The following matrix can be used to determine the limits between an «acceptable» and an «unacceptable» risk with the help of the influential factors mentioned above.

In the example described in Fig. 14, occasional, insignificant injuries are tolerated. A fatal injury is, however, totally unacceptable.

Probability of occurrence Risk acceptance limit

A

frequent

B

occasional

C

infrequent

D

improbable

E

almost impossible

Risk of an injury caused by a rotating saw blade without any safety measures

Area of accepted risk

Curable injury without incapacity to work (reversible)

Limit between «acceptable» and «unacceptable» risks Probability of occurrence At any time

V

Area of unaccepted risk

Never

Severity of harm Severe injuries Fig. 13: Risk limitation.

26

Curable Slight, permainjury nent with incapacity injury to to work health (irrever(reversible) sible)

IV

III

Severe, permanent injury to health (irreversible)

Death

II

Fig. 14: Risk limitation based on a circular saw

Area of accepted risk = residual risk

No injuries

Area of unaccepted risk

I

Severity of harm

13 Risk reduction

For all risks encountered in the area of unaccepted risks, solutions have to be found and applied that reduce the risk originating from the machine to an acceptable degree, i.e. the residual risks.

An example based on a circular saw: Choice of safety measures:

13.1 Choice of safety measures When choosing an appropriate solution, a manufacturer must adhere to the following principles in the order given (cf. Machinery Directive, Annex I): 1. Elimination or reduction of the risks (integration of the safety concept in the development and construction of the machine) 2. Inclusion of safety measures required to combat risks that cannot be eliminated 3. Informing users about the residual risks due to shortcomings of the safety measures adopted; information on special training or personal protection equipment that may be required

1

2

3

Safety measure: first priority:

Safety measure: Safety measure: second priority: third priority:

Elimination or reduction of the risk

Technical safety measures to combat risks that cannot be eliminated

An injurious action

affects

= Fig. 15: Risk reduction.

an incident

Informing users about residual risks and the correct behaviour

a person

Fig. 16: Pivoting safety guard.

1. Avoiding the risk, i.e. eliminating the rotating saw blade, is impossible in this case as the machine would otherwise no longer be able to fulfil its purpose. 2. The harmful effect of the rotating saw blade can be limited by a safety measure, in this case by a pivoting safety guard that encloses the saw blade as far as possible.

27

1

2

3

Elimination or reduction of the risk:

Safety measures Informing users to combat a about residual risk that cannot risks: be eliminated:

Impossible Pivoting safety guard

3. Owing to the incomplete effect of the safety guard, users of the saw must be informed about the residual risks. Among other things, the following information is also given in the operating instructions:

Operating instructions

Warnings on the machine

An injurious action

affects

a person

N When the saw blade is lowered,

coverage is incomplete. Warning: It is forbidden to touch the rotating saw blade.

=

an incident

Fig. 17: Risk reduction based on a circular saw.

N Prior to cleaning, maintenance or

repairs being carried out, the machine must be switched off at the main switch and secured with a personal padlock. N The safety guard must be checked

regularly for correct operation. If the safety guard is faulty, it must be repaired before the machine is started up again. N In order to avoid eye injuries, all

persons working in the area of the saw must wear safety goggles.

Hints on the search for solutions: N The essential health and safety require-

ments relating to the design and construction of machinery in Annex I of the Machinery Directive are binding. N General design principles can be found in

European standard EN 292, parts 1 and 2 (see Bibliography, page 34). N Solutions are listed in the European

safety standards. When implementing harmonized standard solutions, it is assumed that the essential health and safety requirements are fulfilled. However, the following questions must always be clarified precisely: – Is the standard still up to date? – Is the risk situation on the machine to be built actually identical to the risk situation for which the standard solution is intended? – Does the standard not contradict essential health and safety requirements? N The examination of measures that have

been implemented on other machines with comparable risk situations helps to find solutions with an acceptable risk.

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13.2 Assessment of the safety measures The assessment of safety measures is carried out on the basis of the risk assessment described in the procedure in Fig. 1, page 5. This ensures that the safety measure fulfils its purpose and does not create any new risk situations.

Probability of occurrence

A

frequent

B

occasional

C

infrequent

D

E

Risk of an injury caused by a rotating saw blade without any safety measures

Risk of an injury caused by a rotating saw blade with safety measures

improbable

almost impossible

Area of unaccepted risk

Area of accepted risk

Curable injury without incapacity to work (reversible)

V

Curable injury with incapacity to work (reversible)

IV

Slight, permanent injury to health (irreversible)

III

Severe, Death permanent injury to health (irreversible)

II

Severity of harm

I

Fig. 18: Assessment of safety measures based on a circular saw.

29

14 Contents of the technical documentation

Where machinery is concerned, the requirements for the technical documentation (technical file) are described in Annex 3 of the ordinance on the safety of technical devices and equipment (STEV). This description in the STEV largely corresponds to the description of the technical documentation given in Annex V of Machinery Directive 98/37/EC (formerly 89/392/EEC).

«Information» column

More specific information is also given in the Suva publication «Type-Examination Certificate Process for Machinery according to EC Machinery Directive 98/37/EC [formerly 89/392/EEC] (Annex V/VI)», order number CE93-15.e. The description of the solutions selected to prevent the risks originating from the machine represent an important part of the technical documentation.

– List of parts

14.1 Description of the solutions

– Component list for the channels relevant for safety

It is recommended that the results of the risk assessment and risk reduction be entered up in the same table that has been used for the risk analysis. It is important to give a reason for each solution that is finally chosen in the column «Information». For the description of the solutions that have been selected to prevent the risks originating from the machine, the columns «Measures» and «Information» can be used.

– Hydraulic diagram

References must be included wherever supplementary documents are required for the assessment of the solution chosen. Supplementary documents can consist of: – Layout drawings, prospectuses, description – Design drawing – Operating instructions – Strength calculations – Stability calculations – Impact trials, fall trials of guards – Functional schedule of safety devices – Circuit diagrams for the channels relevant for safety

– Pneumatic diagram – Failure effect analysis for the chosen solution – Examination of corrosion issues – List of materials used – Test report – Measurement report

«Measures» column The solution chosen for the fulfilment of the corresponding safety objective must be described and reasons given for its selection. In this way, the choice of solution is comprehensible.

– Component test – Laboratory analysis – Certificates – Declarations by the manufacturer of purchased components – Declarations of conformity for purchased components – ...

30

Risk assessment

Machine: circular saw

Operating mode: Normal operation

Subsystem: . . . . . . . . . . . . . . . . . . .

No.

1.

Description of the operating mode Place profile on support

Probability (P) A B C D E

Death Severe, permanent injury to health Slight, permanent injury to health Curable injury with incapacity to work Curable injury without incapacity to work

Danger situation

No.

1.1

Danger

Cutting with the rotating saw blade

Risk

Person in danger zone

No.

Hand or arm of the operator in the area of the saw blade

1.1.1

1.1.2

*

Severity of harm (S) I II III IV V

Cause

Unexpected start-up after a power failure and operator’s clothing is trapped by the saw blade

Unexpected start-up after a power failure when machine operator is correcting the position of the profile

Incident

Hand- and/ or arm injury

Hand- and/ or arm injury

S

P

III

B

III

B

frequent occasional infrequent improbable almost impossible

Safety objective Nobody must be injured by a rotating saw blade

Nobody must be injured by a rotating saw blade

No.

Measures

Pivoting saw blade guard, warning on the machine, information in the operating instructions.

Pivoting saw blade guard, warning on the machine, information in the operating instructions.

If the saw blade is in the upper end position, the blade is completely encapsulated. During sawing operations, some areas of the saw blade are open. User information in the operating manual and a warning on the machine warn against this residual risk. Assembly drawing no. . . . Saw unit with pivoting guard.

Table 4: Basis for a risk assessment and risk reduction based on a circular saw.

Page 1 of . . . . Signature: ay Date: 15.02.00 Residual risk

Information

S

P

IV

D

*

IV

D

*

31

Risk assessment: Determining the limits of a machine

Intended use, limitations of use: ................................................................................... ................................................................................... ...................................................................................

Space limits: Systems and influences that penetrate the system limits are marked on drawing SN0

Time limits:

Can be copied

Machine: . . . . . . . . . . . . . . . . . . . . . . . . . . .

Operating life of the machine: . . . . . years Wear-out parts:

Operating life:

....................................

.....................................

....................................

.....................................

....................................

.....................................

Life-cycle, operating modes:

The persons involved Users*

Third parties

........

........

........

........

........

Construction Transport Commissioning Use Normal operation ................... ................... ...................

................... Decommissioning Disposal ................... * User training: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...................................................................................

Area of use:

..........................................................................

Date: . . . . . . . .. . . . . .

32

Signature:. . . . . . . . . . . . . . . . . . . .

Page: . . . . of . . . .

Table 5: Table for determining the limits of a machine.

...................

Risk assessment

Machine: circular saw: . . . . . . . . . . . .

Operating mode: Normal operation

Subsystem: . . . . . . . . . . . . . . . . . . . .

No.

Description of the operating mode

Severity of harm (S)

Probability (P)

I II III IV V

A B C D E

Death Severe, permanent injury to health Slight, permanent injury to health Curable injury with incapacity to work Curable injury without incapacity to work

Danger situation

No.

Danger

Person in danger zone

Risk No.

Cause

Table 6: Table for the entry of data on risk assessment and risk reduction.

Incident S

P

Safety objective

frequent occasional infrequent improbable almost impossible

No.

Measures

Page ..... of ..... Signature: ............... Date: ............... Residual risk S

P

Information

Can be copied

33

15 Further information

Federal law on the safety of technical devices and equipment (STEG), SR 819.1, Ordinance on the safety of technical devices and equipment (STEV), SR 819.11, Ordinance on the procedure for the conformity evaluation of technical devices and equipment (VKonf), SR 819.115 N Federal law on product liability,

SR 221.112.944 N Machinery Directive 98/37/EC (formerly

89/392/EEC and its amendments) N EN 292-1:1991

Safety of machinery – Basic concepts, general principles for design – Part 1: Basic terminology, methodology N EN 292-2:1991/A1:1995

Safety of machinery – Basic terms, general principles for design – Part 2: Technical principles and specifications N EN 1050:1996

Safety of machinery – Principles for risk assessment

34

Order number: 66037.e