In any industrial setting, whether in manufacturing, engineering, or warehousing and fulfilment, moving machinery is at the heart of operations. Consequently, machine guards are essential to separate and control access to this equipment, ensuring the safety of the workforce while maintaining optimal operational efficiency. Because different systems pose different risks, specific guards are necessary for different applications to effectively prevent injuries including crushing, severing, shearing, and entanglement.
To ensure both safety and efficiency, engineers and managers must understand the four distinct types of machine guard: fixed, interlocked, adjustable, and self-adjusting. Significantly, they must also understand how these align with specific industrial applications.
Key takeaways
- Fixed guards are the engineering standard for high-risk, low-access zones such as perimeter fencing.
- Interlocked guards are the necessary solution for machinery requiring routine operator interaction, such as loading or cleaning.
- Adjustable and self-adjusting guards are specific point-of-operation solutions for manual tasks where stock must be fed through the hazard.
- Operational context determines the choice: high-speed automation demands different solutions than manual workshops.
Matching the Guard to the Application
While PUWER Regulation 11 provides the legal framework, the practical selection of a guard depends heavily on the nature of the machine and its daily use. The “hierarchy of control” is essentially an engineering logic test: if you never need to access a dangerous part, you enclose it permanently. If you must access it, you need a safe way to enter.
Understanding this operational logic is the key to selecting the correct guard from the four main types.
1. Fixed Guards: The Solution for High-Volume Automation
Fixed guards are physical barriers with no moving parts, robustly designed to totally enclose the hazard. They represent the highest level of protection and are suitable for high-production, repetitive machine operations where operator access to the danger zone is simply not required during normal production.
Why they are used
In sectors such as steel making and other heavy industry environments, the risk comes from large equipment, high-energy processes and hazardous materials such as molten metal. Here, the application demands a barrier capable of withstanding significant impact, often constructed from heavy-gauge sheet steel. Similarly, in warehousing and logistics, fixed perimeter fencing is the only practical way to secure large robotic palletisers or long stretches of conveyor systems. Since operators do not need to intervene while the robot is active, a permanent enclosure is the most effective and robust choice.
Compliance note
To be effective, these guards must be secured by systems that can be opened or removed only with tools, ensuring they remain in place during operation.
2. Interlocked Guards: Enabling Routine Access
When a process demands frequent interaction – such as clearing blockages, loading packaging materials, or performing washdowns – a fixed guard becomes operationally impossible. This is where interlocked guards are applied. These movable guards (doors, gates, covers) connect directly to the machine’s control system via an interlocking device to disengage power the moment they are opened.
Common types of interlocking devices include actuator key (tongue) switches, non-contact magnetic or coded switches (often used for hygiene), and solenoid locking switches.
Why they are used here
Applications are multiple. For example, in the food and beverage sector, high-hygiene standards dictate frequent access for cleaning. Stainless steel interlocked guards allow this routine access without compromising safety during the production run. In other manufacturing operations, such as defence and aerospace, operators may need to enter cells or enclosures for setup or inspection. Interlocked perimeter doors ensure the automated systems are de-energised before the operator enters the cell.
Critical engineering distinction
The application dictates the type of interlock. For machinery with high inertia that takes time to stop (run-down time), such as centrifuges or heavy fans, interlocks with guard locking must be used. These devices physically ensure the door or gate is closed until the hazard has come to a complete stop, preventing the operator from accessing the danger zone while the machine is coasting.
3. Adjustable Guards: The Manual Workshop Standard
In the dynamic environment of engineering workshops and tool rooms, operators work with manual machine tools where the workpiece varies constantly. It is not possible to fully enclose the machine because the operator needs to feed the material directly into the danger zone.
Why they are used here
Adjustable guards are the specific solution for these “point-of-operation” tasks. On a manual drill or milling machine, the operator manually positions the guard to suit the specific size of the workpiece. This provides a barrier that shields the operator from chips, swarf and coolant while allowing the necessary interaction with the material.
Operational risk
Because these rely on the operator to position them correctly for every task, they are less secure than fixed or interlocked systems and require a high level of operator competence and training.
4. Self-Adjusting Guards: Automating Protection for Feed-Through Tasks
Much like their adjustable counterparts, these are used where stock must be fed through the danger zone, but they are intelligently designed to reduce the reliance on the operator.
Why they are used here
The classic application is in woodworking. On a circular saw, a self-adjusting guard is pushed up by the timber as it is cut and springs back to cover the blade immediately after the timber passes. This ensures the blade is covered as much as possible without requiring the operator to stop and manually adjust the guard for each and every cut.
Ensuring the Solution Fits the Risk
While a “suitable and sufficient” risk assessment is the mandatory legal starting point, the selection of the guard is often a logical engineering conclusion driven by the application. As this article shows, the “correct” guard is usually dictated by a clear operational reality: the frequency of access.
Guard types must be aligned with defined operational categories, using fixed guards for isolation, interlocked guards for routine access, and adjustable or self-adjusting guards for point-of-operation tasks. This approach ensures machinery is not just compliant with PUWER, but fundamentally safe and productive.
Partner with the Experts for Robust Compliance
Moving from regulatory theory to a compliant installation is often the hardest step. At Safety Systems Technology (SST), we help you transform safety from a strict legal obligation into a strategic operational advantage.
From impartial risk assessments to bespoke guarding design, we ensure your machinery is safe, compliant, and efficient.
Frequently Asked Questions (FAQs)
How do I know if I need an interlock or a fixed guard?
The decision depends on access frequency. If you need “routine access” for tasks such as loading, cleaning, or clearing jams, an interlocked guard is the correct engineering solution. If access is not required during normal operation, a fixed guard is the preferred standard.
Which ISO standard governs the design of fixed guards?
The primary Type B standard is BS EN ISO 14120. This standard stipulates that fixed guards must be secured by systems that can be opened or removed only with tools. Crucially, it also mandates that fixing systems (such as screws or nuts) must remain attached to the guards or the machinery when the guards are removed to prevent loss.
Can I use adjustable guards on automated machinery?
Generally, no. Adjustable guards are point-of-operation solutions for manual tasks where stock is fed through the guard. Automated lines typically require fixed guarding or interlocked perimeter fencing to prevent access entirely.
What determines if I need guard locking?
The mechanics of the machine. If the dangerous parts continue to move after power is cut (run-down time), you must use guard locking to prevent the door from opening until the motion has stopped.
What is the key standard for interlocking devices?
BS EN ISO 14119 is the critical standard regarding interlocking devices associated with guards. This standard provides the framework for selecting the correct device – distinguishing between a standard interlock and one with guard locking. It also includes stringent requirements for anti-tampering design.
How do I know how far away to place a guard to prevent reaching in?
You must ensure the guard prevents access to the dangerous part, often determined by “reach distances”. While PUWER provides the requirement, engineers typically refer to BS EN ISO 13857 (Safety of machinery: Safety distances to prevent hazard zones being reached by upper and lower limbs) to determine the exact measurement required based on the gap size in the guard.
Are light curtains considered one of the four types of guard?
Technically, no. The four types (fixed, interlocked, adjustable, self-adjusting) are physical barriers. Light curtains are classified as protection devices. However, under the PUWER hierarchy of control, if physical guarding is not practicable (for instance, where an operator needs constant hands-on access), you are legally permitted to use protection devices such as light curtains to stop the machinery before a person enters the danger zone.
Is a CE/UKCA mark enough to confirm the guarding is correct?
No. The mark confirms safety at supply as specified by the Supply of Machinery (Safety) Regulations 2008 (SMSR). However PUWER requires employers to ensure ongoing safety once installed. The employer must verify compliance within the specific operational environment and conduct regular inspections throughout the equipment’s lifecycle.
