UNI EN ISO 14119 WILL REPLACE UNI EN 1088

UNI EN ISO 14119 WILL REPLACE UNI EN 1088

UNI EN ISO 14119 will replace UNI EN 1088 interlocking devices for mobile guard protections, what's new:

The use of guard locking devices on safety doors is a well tested practice for the protection of machines with overtravelling movements. The interlock system prevents the door from opening until the machine has come to a complete stop. Such a safety feature is ensured by fitting a safety switch with an electromagnetic locking device and a solenoid pin which is unlocked only after receiving a specific set signal.

The currently valid standard UNI EN 1088 makes the assessment of the correct safety switch a complex matter, on the other hand the new EN ISO 14199 standard promises to simplify such an assessment by supplying clear recommendations. 


The new standard EN ISO 14119 procedure

At present the current valid standard is the UNI EN 1088 “Safety of machinery – Interlocking devices associated with guards – Principles for design and selection”, legally adapted to fit the requirements contained in the new Machinery Directive 42/2006. This standard was enforced in 1995 and underwent minor revisions in 2005 and 2008. In 2011 a major revision project, named EN ISO 14119, was introduced and it is presently being considered for approval by the technical committee for machinery safety ISO TC/99. The final draft is expected to be ready in the first months of 2013.


Assessment of the locking device standard along with an example 

We will use an example to describe the designing procedure: a textile printing machine, whose main danger is associated to the rollers' high speed rotation and their inertia even after stopping the machine (also in case of emergency).
At an early stage, risk analysis can be carried out by following the recommendations in EN ISO 12100 or its type C equivalent standard: UNI EN ISO 11111.
Such a risk analysis highlights danger of both lower and upper limb crushing due to the movement of the textile winding rollers, hence the safety solution prescribed is to fit a guard fencing system. The size of such a protection will need to be calculated according to the recommendations outlined in UNI EN ISO 953, Uni EN ISO 13857. The project will, as a result,  necessarily include access points for the unloading of the final product or for maintenance operations. Such protection doors will also need to be equipped with a safety switch, which in turn means that a switch assessment must be carried out in order to verify if it needs to be associated with an interlocking device with solenoid pin to delay opening until the rollers have come to a complete stop after the machine stop command has been activated.
 

         

 

To complete such a risk analysis, the assessment of the safety distance must be carried out in conformity with the EN ISO 13855 standard, which defines the procedure to follow for the calculation of the distance of doors/access points from the danger area. Section 9 describes the minimum distance requirements in order to prevent any type of hazards after door un-locking during over-travelling movements.
Such a distance is calculated as follows:

S = (K x T) + C

in which:

S   represents the minimum distance in mm 

K   represents a constant factor indicating the approach speed – intrusion speed of a body or part of body in mm/sec 

T   represents the total time (t1+t2) needed for the machine to be considered totally safe  expressed in seconds 

C   represents the intrusion distance in mm, protection guard distance from danger as defined by  UNI EN ISO 13857

The approach speed is a constant factor equivalent to 1600 mm per second, so in the case of the textile printing machine in our example, we estimate that the distance from danger to the un-locking of protection C is 500 mm.

The design engineer has calculated that the total stopping time t1+t2 is 5 seconds (where t1 is the time the control system needs to detect the alarm signal and t2 is the time the machine needs to come to a complete stop)

So:

S = (1600x5) + 500 = 8500 mm

Considering such a result, it is quite evident that the resulting distance means that an interlocking system with a guard locking device needs to be installed. Such a system will allow the machine to come to a complete stop and restore the machinery safety conditions before the doors are un-locked thus allowing the installation of the protection guards at the required distance.

Such an analysis suggests that UNI EN1088 must be consulted in order to choose the most appropriate component.  
 
The basic requirement is that the locking device can be unlocked only by energy and locked by spring force, but the standard also regulates the cases in which a different principle should be applied. For example in case of fire within the plant when firefighters need to be granted access even in the event of power failure. In this case the new EN ISO 14119, unlike EN 1088, recommends that in such an event the access to the machinery in emergency conditions should be ensured by an emergency unlocking device associated to the interlocking system, which allows its un-locking without using tools.

The requirement which follows, which has been retained unchanged in EN ISO 14119, states that the locking position of the locking system must be controlled in order to prevent the machine being started if the locking system is not effectively locked.

The associated safety function is the monitoring of the interlocking system's locking device, which must be designed according to the risk analysis. In our example the category to be reached is 4 because  EN ISO 13849-1 requires that the PLr to be reached is “e”.

Electronic monitoring is usually carried out by a single dual-channel sensor. Nonetheless, categories 3 and 4 clearly require two sensors. Does this necessarily imply that two intelocking systems should be mounted on the access point?

EN ISO 14119 answers this question by stating it is possible to apply the “fault exclusion” principle to possible failure of the interlocking systems even for PLe and SIL3. In other words a single interlocking system can be used.

Another question is if the locking control device is relevant in terms of “safety assessment” (13849), and if so how should the assessment be carried out? 

The new EN ISO 14119 answers this question too, but unfortunately the answer is not as clear cut. A comment suggests that the interlocking system's PL (Performance Level) is generally lower than the PL of the control system for that position.

Such a suggestion relies on the belief that the chance of danger resulting from the failure of such a system is rare. The reason is to be found in the fact that the circuit which monitors the locking position of the safety switches, cuts the machine off as soon as the locking device control allows the incorrect opening of the doors. Therefore, danger caused by the over-travelling movements of a machine exists only in such a case. To conclude, in many practical applications, the result will be a single control channel which fulfills the PLr requirements in the risk assessment.

Let's take a step further by stating that, generally speaking, interlocking systems must integrate another key safety function for the prevention of accidental machine re-start, therefore the choice of the most appropriate component to use will need to verify the presence of a device which prevents switch locking (which allows machine re-start) if the door (in our case) to which it is associated is not locked too, and that the command is carried out intentionally. The new ISO 14119 defines such a device as Failsafe.

The new  EN ISO 14119, will allow an overall much easier assessment of the electromagnetic devices thanks to a much clearer description of the procedures to follow. Moreover, the new standard will include a simplified assessment of tampering risks and the description of how to connect to a control system correctly. Nonetheless, these represent only a part of the modifications included in the EN ISO 14119, therefore further in-depth analysis will follow very soon.

 

         
 

Access designs modular guard fencing systems and our Perimetra project caters for functional safety by designing safe guard fencing systems which do not negatively impact on the plants productivity.
Our products and projects are certified according to the CE machinery directive and comply with the regulations type B and C.

 

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