Key Concepts of Machine Safety Verification and Validation
Brian Haury, PE,
Senior Manager
Safety First
At Matrix Technologies, safety is one of our core values. In fact, we have a program called “Believe in Zero,” which means we strive every day to not have a reportable OSHA incident. We provide all necessary protections for our employees, and we put their safety first.
Our concern about safety extends to our customers as well. How do we strive to ensure our customers’ safety? We work hard to guarantee all industrial safety systems we engineer are up to relevant safety standards and pass the key tests of verification and validation.
Starting with Standards of Safety
Every industrial worker’s workplace should be, as OSHA puts it, “free from recognized hazards that are causing, or are likely to cause, death or serious physical harm.” In some cases, safety systems are designed and installed to lower the probability or frequency of hazards to achieve the level of safety that is required. In these cases, a safety device or safety system should work as it was intended (e.g. stop the machine, slow down operation, move to a safe position, etc).
While designing systems for industrial applications, we conduct a risk assessment: we identify potential hazards, analyze who can be injured and how, and develop safety measures to mitigate the risk. These safety measures might include devices and systems such as estop push buttons, safety switches, safety contactors, and more. To ensure these devices and systems will react as intended, our engineers put them through the processes of verification and validation.
Verification and Validation: Ensuring Safety through Two Distinct Processes
Verification is the process of comparing a safety circuit design and its components to the appropriate safety standards to determine if they meet or exceed the safety level determined by the risk assessment. After the safety circuit is designed and before it is installed, our Matrix engineers use SISTEMA, a widely-known software tool, to accomplish a safety system verification for the control standard of EN ISO 13849-1. The software allows our engineers to model the structure of the safety devices in the system and input the relevant parameters to determine the achieved Performance Level (PL) of the safety system.
Validation is the process of checking the possible fault conditions of the safety system after it is installed to make sure it functions to the safety level required by the risk assessment. This process may involve lifting wires, shorting contacts, removing power, etc., to simulate the possible fault conditions.
The best way to visualize the difference between these two processes is to look at the two simple houses below. Knowledge of the appropriate standards is required to verify the design and build both of the houses. However, only after the houses are built and installed can we validate that only the house on the right was installed properly.
Similarly, safety systems can function in unexpected ways after installation and should be validated before production begins. A simple example would be a safety area scanner used to detect the presence of a person roughly 10 feet from an automatic saw blade used to cut tree logs. In theory, if a person were to walk near the saw, the safety area scanner would detect the person and cut power to the motor of the saw; however, two major problems can occur that may not have been caught during the design and verification steps:
First, dust will be created from cutting the logs, which can inhibit the scanner’s ability to detect a person.
Second, the saw blade would be considered a high inertial load, which means the saw blade will continue to spin on its own even after power is removed from the motor. This freewheel spin can continue for several minutes depending on how fast it was running and the friction of the system before the blade eventually comes to a stop.
The Solution
When problems like these come to light during the safety system validation, it is necessary to find good solutions. For the scenario above, one possible solution could be to install a locking gate sensor with a zero-speed switch on the shaft of the saw blade in lieu of the area scanner. The zero-speed switch would detect the rotation of the saw blade and would only unlock the gate allowing access to the saw when it was no longer rotating. This system would take into account the environmental conditions and the high inertial load of the saw and would pass both the safety system verification and validation after it was installed.
When designing and installing a safety system, performing both a safety system verification and a safety system validation are critical steps in the machine safety lifecycle to ensure that the safety devices work as intended. Skipping these steps could leave fault conditions unprotected, leading to possible harm in the workplace.
Matrix Technologies is one of the largest independent process design, industrial automation, engineering, and manufacturing operations management companies in North America. To learn more about our safety verification and validation services, contact Carl Bohman, PE, FS Senior Project Engineer (TUV Rheinland).
