Key points
Industry 4.0 has garnered the rapid evolution of machine technology and enhancements for smart devices and data management. As a result, engineers face increasing pressure to implement not just the latest, but the safest technologies, thus ensuring the protection of both people and machinery.
This ambition necessitates the development of system solutions that foster performance and efficiency, while simultaneously aiding the design and implementation of safe systems.
As a technology provider, the goal is to help engineers eliminate the potential for accidents by supplying innovations that follow fundamentally safe design principles.
Rapid machine technology advances in the area of factory automation have created increased emphasis on smarter controls and greater integration of smart devices and safety componentry.
Included within this thinking are the latest pneumatic solutions, which have today become an integral part of safety controls for implementing the preventative technical measures required to make machinery safe, including clamping, blocking, exhausting and holding equipment in place.
Safety components within the Machinery Directive
Of course, the Machinery Directive is a key part of safety in industry and provides the reference for all new machine development projects. Based on the Machinery Directive, EN 13849-1 (Safety of Machinery) and EN 13849-2 (Validation) build the procedure of assessing machine safety and the safety-related parts of control systems (SRP/CS).
The new standards of 2006/42/EC replace the standards previously used under 98/37/EC, which now better define areas that include safety components, partly completed machines and other specific machinery topics.
So, what classifies a product as a safety component? Well, under the terms of the Machinery Directive, a product is deemed to be a safety component when it is tested and verified to provide specific safe function for a pre-determined period of time in a given state. The product must bear the CE mark for Europe and receive independent certification.
Within the Machinery Directive there is clear distinction between safety devices and standard pneumatic components used in a safety circuit. Importantly, the term safety component does not imply the reliability or safety level of the component. Those products offered as safety rated must undergo stringent requirements for certification, testing and approval.
As a further point of note, the Machinery Directive does not prescribe the use of safety rated componentry; it only offers a description of the conformity assessment procedures to market a product as safety rated.
These conformity procedures include: a guarantee that the product will perform a safety function; that the product be marketed separately as a safety product; and that the product will bear the CE mark. As such, all safety components are evaluated by their manufacturer for safety function.
Risk reduction by analysis and evaluation
To determine what level of safety is required, a risk assessment is required. Risk assessments are a series of logical steps to enable the analysis and evaluation of the risks associated with a full or partial area of a machine, and to take action, if necessary, to ensure risk reduction. The overall process comprises three steps: analysis, evaluation and reduction.
Risk analysis begins with determining the limits of the machinery. Here, engineers must consider all stages of the machine’s life cycle, including the relevant people involved, the environment and the products used.
As part of the same step, hazards must be identified that allow the machine designer to take corrective action early in the design process and prevent potential harm from occurring.
Risk analysis also requires engineers to estimate risk and determine the performance level required (PLr). Each hazardous situation is classified by five performance levels, from a to e.
The next step is risk evaluation. Should the conclusion be that risks exist on a machine, it is incumbent upon the machine designer to determine how best he or she can eliminate those risks and implement changes for risk reduction.
Prior to commencing this process, it is often helpful to break a larger machine down into workable sections (known as zones or modules), such as the cutting zone, feeding zone and so on.
Finally, risk evaluation is followed by risk reduction. Ongoing iteration of this process is necessary to eliminate hazards and adequately reduce risks through the implementation of protective measures wherever designing out the hazard is not possible. Furthermore, engineers must ensure that changes do not create additional potential risks in other areas of the design.
Determining performance level
After the PLr is established and the risk assessment has been completed, the performance level (PL) will need to be determined based on safety categories that are established according to factors such as a measure of diagnostic capabilities (DC) for the control system, the mean time to dangerous failure (MTTFD) and common cause failure (CCF). Together, these inputs will define the level of a given safety function.
DC is a requirement of any safety-related control system. The degree of DC will vary based on the PL needed. When a dangerous failure occurs, it is the monitoring quality of the control system which will detect the fault and bring the machine to a safe state. DC is therefore a very important part of achieving the PL requirements.
The reliability of a system has to be quantified as part of achieving a desired PL. Reliability is expressed as MTTTD, which in essence is a statistical calculation that defines the mean time (usually expressed in years) until a dangerous failure occurs in a component.
While there are no guaranteed values when it comes to statistical calculations, the idea is to understand the probability of failure within a system.
CCF is the failure of a component for one common reason, or failures stemming from a common source, such as contamination or excessive heat. Measures must be implemented to combat potential failures of this type.
These variables work together to ensure that safety is not just focused on component reliability, but instead introduces common sense safety principles such as redundancy, diversity and fail-safe behaviour of safety-related control parts.
When determining the PL, the greater the risk, the higher the requirements of the control system. EN 13849 dictates that the machine is safe when the PL of the safety control circuit is equal to or greater than the PLr of the application.
In summary
The stark reality is that no margin for error exists whenever safety is involved. Rather than viewing machine safety as little more than working through the Machinery Directive to tick the relevant boxes, performing real life risk analysis, evaluation and reduction is a far safer way of getting things right.
In tandem with this strategy, peace-of-mind can be assured by using safety-rated products from a reputable supplier. As almost all machine builders will be aware, the price of non-compliance does not bear thinking about.
