How do I validate my Safety System?

The most common step that is not performed or performed incorrectly when implementing a safety system is validation. This step is essential to confirm the specification and conformity of the safety system, however many people are unsure how to validate or don't even consider performing a validation.

Here are some common mistakes made with validation:

No Specification

You can’t validate an unspecified safety system, thus if there is no specification document then what are you validating?

The specification document has two purposes:

1. It provides a framework for the system to be designed
2. It provides a specification to validate

The specification should explain the following:

1. The functional behaviour of the safety system - For example if the system is an E-Stop the specification should explain; how the E-Stop is initiated, what hazardous movements are inhibited by the E-Stop, what Stop Category is performed, how quickly are these movements inhibited, how is the system reset to allow machine operation to continue, etc.
2. Operational and environmental conditions
3. Integrity Requirements - What is the level of risk reduction required by the safety system? This can be measured by a required Safety Category (CAT), Performance Level (PL) or Safety Integrity Level (SIL)

Once the Specification exists then the system can be validated according to its functional, environmental and integrity requirements.

Only Normal Operation of Safety System is Tested

It is common for validation to be performed on a safety system with no fault simulation testing.

For example, if validating an E-Stop the machine is started under its maximum expected operational load and the E-Stop hit. The safety function is validated by confirming the hazardous movements have been ceased in the required time according to the specification and the machine can’t be restarted until the E-Stop operator is manually reset.

The above validation may prove the functional behaviour of the E-Stop but many safety systems also require fault simulation to validate their integrity requirement. If the above E-Stop had a requirement of CAT 3, then all single fault modes would need to be simulated to confirm that the system will not lose safety function due to a single fault.

No Documentation

As like any activity performed during the implementation of a safety system, validation does not exist if it is not documented. All relevant analysis, tests reports, calculations, data sheets, etc. must be recorded to prove the process undertaken.

For help with validation plans, register for the NHP Safety Reference Guide, in the 'Safety Function Document' section there are numerous examples of pre-engineered Safety Functions with validation plans at the back of each document.

For more information on the process of validation, activities to be performed and the documentation required reference AS 4024.1502-2006.

New Guidance on Machinery Risk Assessments

Risk assessment on machinery is a major area of uncertainty for a large proportion of industry. It's quite common for people given the responsibility of risk assessment to be unsure of the process and fearful of being held accountable for results of the risk assessment.

While codes of practice do provide good guidance for the general process of risk assessment, they don't cover the unique challenges of machinery applications. Unfortunately, the 2006 version of the Australian Machine Safety Standards (AS 4024.1) provided only theoretical guidance for risk assessment and left many people still confused on issues such as:

• Who should be involved in the process of risk assessment?
• Systematic methods to identify hazards on the equipment
• What risk estimation tools are available and how do they work?
• What does documentation of risk assessment actually looks like?

Guidance is now available in the 2014 revision of Australian Machine Safety Standards (AS 4024.1). A new standard, AS 4024.1303:2014, has been created, which provides practical guidance on risk assessment for machinery.

This standard gives detailed information on how to set-up and prepare for a risk assessment. Advice is provided on who should be part of the team and what information should be collected to prepare for the risk assessment.

The standard also explains systematic approaches for hazard identification. For example, the top-down approach starts with defining the hazardous situations of a machine and then analyzing the hazard zones.

One of the major improvements with this standard is the information that is provided for risk estimation. This standard now explains various risk estimation tools such as Risk Matrix, Risk Graphs, Numerical Scoring and Hybrid Tools.

If you are confused about how the process is actually implemented and what the documentation looks like then Annex A of AS 4024.1303:2014 should provide some answers. This Annex explains step by step the risk assessment process carried out on a molding machine, it also shows all the documentation created during this process and explains what risk reduction measures were used.

With this new standard, AS 4024.1303:2014, you have access to information to help you facilitate risk assessments on your machinery. If you would still like assistance with the risk assessment process contact NHP's customer service team or contact your NHP sales representative.