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Machinery Safety Standards

Hierarchical Structure of International Standards Concerning Machinery Safety

IEC/ISO Guide 51, jointly prepared by IEC and ISO as a criterion for establishing standards concerning machinery safety stipulates the following classification of international standards. This structure is applicable even to machinery manufactured based on the latest technologies.

Type A Standards: Basic safety standards

Standards specifying basic concepts and design principles that can be applied to all machines.

Type B Standards: Group safety standards

Standards specifying safety that can be applied to a fairly wide range of machine groups Type B Standards can be further divided into two categories of Type B1 and B2 Standards as follows.

Type B1 Standard:	Standards related to specific safety aspects, such as safe distances or noises
Type B2 Standard:	Standards related to safety-related devices such as light curtains or interlock devices

Type C Standards: Individual product safety standards

Standards specifying detailed safety requirements for a specific machine or a group of machines

Machines to which Type C Standards are applied need to be designed according to Type C Standards. Otherwise, machines need to be designed according to both Type A and Type B Standards.

Types of standards and areas to which they apply

Concept of Machinery Safety in International Standards

Purpose of ISO12100

The purpose of the establishment of ISO12100, which is positioned as the standard for basic concepts of machinery safety are as follows (ISO12100－1 Introduction):

	To provide comprehensive framework and guidance to enable the design of machinery which is safe in the scope of specifications.
	To provide a guideline for strategic creation of Type B and Type C standards that harmonize with ISO12100 rated as Type A standards.

For the purposes above, two articles have been established: ISO12100-1:2003 "Safety of machinery-Basic concepts, general principles for design-Part 1: Basic terminology, methodology " and ISO12100-2: 2003 "Safety of machinery-Basic concepts, general principles for design-Part 2: Technical principles".

ISO12100-1 specifies the sources of hazard which must be considered
in designing machinery and the strategies for reducing risks. ISO12100-2 specifies
the approach to inherently safe design, the protective measures,
and the method of providing information to users.

Sources of Hazard Specified by ISO12100

ISO12100-1 specifies the following eight sources of hazard:

Mechanical hazard

Hazard caused by machinery or part of machinery such as being crushed, severed, or entangled, and receiving impact or lacerations

Electrical hazard

Hazard caused by electric shock, due to contact with a current-carrying part, static electricity, or lightning

Thermal hazard

Hazard caused by contact with a hot part, or work under high- or low-temperature conditions

Noise-related hazard

Hazard such as loss of hearing ability, ringing ears, or loss of sense of balance

Vibration-related hazard

Hazard such as poor blood circulation, neuropathy, or articular disorders

Radiation-related hazard

Hazard caused by X-rays, low frequency, radio frequency, microwave, or ultraviolet rays

Chemical substance-related hazard

Hazard caused by inhaling harmful substances or by explosion

Ignorance of ergonomics-related hazard

Hazard such as physiological effects caused by a strained posture or other causes

What is Risk?

ISO12100-1 defines risk as "the combination of the probability of occurrence of harm and the severity of that harm". It also defines harm as "a physical or health disorder". Consequently, the risk stated in ISO12100-1 is thought to be limited to on-the-job accidents and injuries.

ISO12100 was established based on the idea that there is no absolute safety. In other words, some risk remains. The idea is that "safety" is achieved by reducing this remaining risk (residual risk) to a level accepted by the public sense of values and notions at the time (acceptable risk).

Reducing the residual risk to an acceptable level is achieved by a process that repeats risk assessments and risk-reducing measures.

Risk Assessment and Risk-Reducing Measure

The following chart describes the flow of the risk-reducing method specified by ISO12100.

Risk assessment

The area enclosed by a broken line corresponds to the risk assessment specified by ISO14121. The risk assessment steps (1 to 4) are explained as follows:

1. Specify the specifications of the target machine
Limit the specifications of the target machine. In other words, limit the machine usage, installation environment, and time.

2. Identify the sources of hazard
Identify the sources of hazard specified by ISO12100-1 within the scope specified in step 1.

3. Estimate the risk.
After the sources of hazard are identified, estimate the risk by determining risk factors for each source of hazard.
A risk factor can be determined from the combination of the level of injury (severity) and the probability of occurrence.

4. Evaluate the risk
Evaluate the necessity of risk reduction and the achievement of safety for the risk estimated in step 3. If risk reduction is necessary, take concrete risk-reducing measures.

Risk-reducing measure [Based on ISO12100-2]

A. Inherently safe design
The standard explains that risk reduction can be achieved when the machine is designed based on a design including no sources of hazard or by selecting a proper design approach. Inherently safe design means taking measures to avoid/reduce risk at the design stage. For a description of specific design approach, refer to ISO12100-2: 2003, Section 4.

B. Safeguarding by additional protective measures
When the conclusion of rational judgment is that the inherently safe design approach cannot eliminate the source of hazard or cannot reduce the risk, a guarding facilitiy for human protection or a safeguarding device must be used. KEYENCE's safety light curtains can be used as protective devices defined as AOPD (Active opto-electronic protective device) by ISO12100-1. For a description of safeguarding measures, refer to ISO12100-2: 2003, Section 5.

C. Providing information to users
ISO12100-1 considers that providing information to users is part of machine design. All the information necessary to operate the machine properly and safely must be given to the users. The information provided to the users includes warnings and cautions which are appropriate to the level of users as well as the information of residual risks. For a description of methods to provide information, refer to ISO12100-2: 2003, Section 6.

Safety Categorization and Category Selection

Selecting safety category

ISO13849-1 includes the chart on the right as an evaluation example of the safety measure for risk reduction against the risk estimated by the risk assessment. Where,

S:	Severity of the injury
S1:	Not serious (recoverable)
S2:	Serious including death (unrecoverable)

F:	Frequency and/or duration of exposure to sources of hazard
F1:	"Seldom" to "sometimes" and/or short duration
F2:	"Frequent" to "continuous" and/or long duration

P:	Possibility of avoiding the source of hazard
P1:	Possible under specific conditions
P2:	Almost impossible

The symbols for category selection express the following meanings:

●：	Category recommended for the risk.
△：	Category where additional safety measures are required for the risk.
○：	Category of excessive measures for the risk

Requirements of each category specified in ISO13849-1

Category	Requirement	Operation of control system
B	The safety-related section of the control system or protective device must be designed, configured, selected, and assembled according to appropriate standards in order to resist conceivable external influences.	When a fault occurs, the safeguarding function will be lost.
1	Satisfy the requirements for Category B. Use carefully selected parts which provide high reliability. Observe the safety principles.	When a fault occurs, the safeguarding features will be lost, although the possibility of occurrence is lower than that of Category B.
2	Satisfy the requirements for Category B and observe the safety principles. The safeguarding features must be checked by the control system at proper intervals.	When a fault occurs during the interval, the safeguarding features will be lost. The loss of the safeguarding features must be detected by the check.
3	Satisfy the requirements for Category B and observe the safety principles. Design the safeguard-related sections according to the following principles: 1. The safeguarding features will not be lost due to a single fault. 2. The system is designed, as much as possible, to be able to detect a single fault.	Even when a single fault occurs, the safeguarding features will be retained continuously. Not all faults can be detected. If undetected faults accumulate, the safeguarding features will be lost.
4	Satisfy the requirements for Category B and observe the safety principles. Design the safeguard-related sections according to the following principles: 1. The safeguarding features will not be lost due to a single fault. 2. A single fault can be detected at the time of or before the next activation of the safeguarding features. Even if this is impossible, the safeguarding feature will not be lost due to accumulated faults.	Even when a single fault occurs, the safeguarding features will be retained continuously. Faults are detected before the activation of the safeguarding features so that the features will not be lost.

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