Machine Guards: Fixed, Movable and Interlocked

By what rule are machine guards fitted?

An arm caught in a belt-and-pulley drive, a lathe chuck left exposed, or a hand reaching into a press die: what these accidents have in common is contact with a moving part. Machine guards are the first and most reliable barrier against this contact. In this article we explain the types of guard, which one to choose where, and the most difficult topic: how to prevent guards from being removed and disabled on site.

The basis is the Regulation on Health and Safety Requirements for the Use of Work Equipment (Official Gazette 25.04.2013, No. 28628). Under Annex I item 2.8, where mechanical contact with moving parts could lead to accidents, the equipment is fitted with guards or protection devices that prevent access to the danger zone or stop the moving parts before the zone is reached. Item 2.8.1 lists the requirements guards must meet:

They are of robust construction and do not give rise to any additional hazard.
They cannot easily be removed or rendered ineffective.
They are located at an adequate distance from the danger zone.
They do not restrict the view of the operating points.
They restrict access only to the area where work is done; fitting, removing parts and maintenance can be done, if possible, without removing the guard.

Art. 5 of Law No. 6331 on Occupational Health and Safety also requires risks to be combated at source and collective protective measures to be given priority over personal protection. Gloves or glasses give no protection against an exposed gear; the solution is on the machine.

Types of machine guard at a glance

The design and construction requirements for types of guard are defined in TS EN ISO 14120, interlocking devices in TS EN ISO 14119, and reach distances in TS EN ISO 13857. The Ministry of Labour and Social Security's mechanical guarding training module uses the same classification.

Type	How does it work?	Typical use	Point to watch
Fixed enclosing guard	Encloses the danger zone on all sides; removed only with a tool	Belts and pulleys, gearboxes, shaft ends	Must be refitted after maintenance, with all fasteners present
Fixed distance guard	Does not fully enclose; prevents access by its size and distance	Robot cell fencing, conveyor tunnel	Height and opening chosen according to distance from the hazard
Movable guard	Opens on hinges or slides without a tool	Machine front door, feed cover	Gives no protection on its own; needs an interlocking device
Interlocking guard	Hazardous function stops when opened; does not start by itself when closed	CNC door, packaging machine covers	The machine must be able to stop before a hand reaches the hazard
Interlocking guard with guard locking	The door stays locked until hazardous movement has ended	Shafts that continue to rotate under inertia, centrifuges	The lock must not open before standstill is detected
Adjustable guard	Its position is adjusted to the workpiece	Circular and band saws, pillar drill	Correct adjustment depends on the operator; training essential
Sensitive protective device	Not a physical barrier; detects the person and stops the machine	Press feeding, robot cell entry	Gives no protection if not fitted at the correct distance

Why is a fixed guard the first choice?

Fixed guards are simple and contain no sensor or circuit that can fail. The Ministry module also stresses that they should be the priority choice wherever possible. The rule is simple: if the worker does not need to access the danger zone during normal production, that zone is closed off with a fixed guard.

The mistakes we see most often on site are:

Wing nut or hand-operated catch: A fastening that needs no tool effectively turns the guard into a movable guard. A fixed guard should be removable only with a tool.
Wide-mesh wire cage: The larger the mesh opening, the further the cage must be from the hazard. If a finger or arm can pass through the opening and reach a moving part, the cage is not doing its job.
Missing screws, panels held with tape: A guard refitted incompletely after maintenance should be treated as if it were not there.
Reaching under or over: If the fence does not go down to the floor or is too low, the worker can reach the hazard by bending or stretching.

Movable and interlocking guards

If the operator needs to access the danger zone many times a day to load parts, make adjustments or clean, a fixed guard is not practical and starts to be removed. In this case a movable guard is used; but a movable guard alone is not enough, it must be connected to the machine's control system by an interlocking device (interlock).

A well-designed interlocked door is expected to behave as follows:

While the door is open, the machine's hazardous functions cannot be started.
If the door is opened during operation, a stop command is given and remains active while the door is open.
Closing the door does not start the machine by itself; a separate command is needed to restart.

Think of a CNC lathe door: if the chuck stops when the door is opened and the machine runs only when the operator presses the cycle start button after the door is closed, the arrangement is set up correctly. If the chuck starts turning as soon as the door closes, that is a design or fault problem.

On some machines, movement continues for a while after energy is cut: large saws, centrifuges, drives with heavy flywheels. Even if a stop command is given when the door is opened, the shaft continues to turn under inertia. In this case an interlocking guard with guard locking is needed; the door stays locked until hazardous movement has completely ended.

Light curtains and other sensitive protective devices

In jobs with frequent hand entry, such as press feeding, sensitive protective devices such as light curtains, area scanners or pressure-sensitive mats are used. These devices do not create a physical barrier; they detect a limb approaching the danger zone and stop the machine. They therefore depend on two things: how quickly the machine stops and how far from the hazard the device is fitted.

Other points to watch with sensitive protective devices:

A curtain protects only its own plane. If there is access from the sides, above or below, those directions are closed with fixed guards.
A light curtain gives no protection against ejected parts, splashing liquid or sparks.
Two-hand controls protect only the operator pressing the buttons; they do not protect a person behind or beside the machine.
Muting functions that temporarily disable the curtain should operate only in situations foreseen in the design.

We will cover safety distances and two-hand control requirements on presses in detail in a separate article.

How can guards being disabled be prevented?

Guard removal is usually seen as a "discipline" problem; yet there is usually a reason behind a removed guard: loading the part is difficult, the guard has to be opened constantly for adjustment, the cover blocks the view of the operating point, or the sensor often gives faults. This is exactly why the regulation contains the requirements "not restricting the view of operating points" and "maintenance can be done without removing the guard".

The approach we apply consists of the following steps:

Ask why. For every guard removed or bypassed, talk to the operator and record the event as a near miss.
Fix the design. Use transparent polycarbonate instead of a sheet metal cover that blocks the view, and an interlocking door instead of a fixed cover that is opened often.
Make tampering harder. Choose coded or RFID interlocking devices instead of simple switches that can be defeated with a magnet or spare actuator; mount the device where it is not easily reached.
Define a safe way for maintenance and adjustment. Under Annex I item 2.13, maintenance is done while the equipment is shut down, its energy connection cut and all movement stopped. Put the energy isolation and lockout steps in writing.
Check at the start of each shift. Make sure that guards being in place and the interlock working are on the operator's daily checklist.
Put bypass decisions on record. If an interlock is to be temporarily out of action because of a fault, the machine is not run in production; the maintenance team's decision and the reinstatement date are recorded.

A checklist you can use in inspections

When doing machine walks at metalworking, automotive supply and food plants in Bursa, we ask these questions:

Are all moving parts (belts, chains, gears, shaft ends, couplings) enclosed?
Can fixed guards be removed only with a tool?
Are cage and fence openings appropriate for the distance from the hazard?
Does the machine stop when the interlocked door is opened, and does it start by itself when it is closed?
On equipment that rotates under inertia, does the door stay locked until movement has ended?
Has the light curtain's stopping time been measured and the distance set accordingly?
Who checks that guards have been refitted after maintenance?
Is there a record of guard removal or bypassing in the last three months, and has the cause been eliminated?

The answers to these questions should be entered directly into the risk assessment. If you score with the Fine-Kinney method, the difference between the probability score of a machine with its guard removed and the same machine with its guard working clarifies the improvement priority. For examples specific to food machinery, see our article on mincers, dough mixers and slicers. Also plan the annual periodic inspection of machine tools such as presses, press brakes, guillotines, lathes and milling machines according to the intervals in the periodic inspection intervals guide, and track the dates with the OHS calendar.

In the metal and machinery sector, screening the machine fleet for guarding and preparing an improvement plan is part of the site work of Bursa Sistemer OSGB's OHS specialist services; we transfer the findings to the risk assessment document as actions with owners and deadlines.

Frequently Asked Questions

Does a cover held with wing nuts count as a fixed guard?

No. A fixed guard is one that can be removed only with a tool. A cover that can be opened by hand behaves in practice like a movable guard; if it is opened often it should be fitted with an interlocking device, and if it does not need to be opened it should be converted to a fastening removed with a tool.

Can we make guards ourselves for an old machine without a CE mark?

You can; the employer is obliged to bring every item of work equipment it uses into line with the minimum requirements in Annex I of the regulation. The guard's openings and distances should be designed according to TS EN ISO 13857 and the interlocking device according to TS EN ISO 14119; the risk assessment should be updated after the change.

Does a machine with a light curtain also need fixed guards?

Usually yes. The curtain detects access only in its own plane. Areas that can be reached from the sides, rear, above or below should be closed off with fixed guards. If there is a risk of ejected parts, the curtain gives no protection against it.

What should we do if the machine does not stop when the interlocked door is opened?

Take the machine out of use immediately, hang a visible warning on it and do not run it until the fault has been repaired and a function test carried out. Record the event as a near miss; also check other machines with similar interlocking devices.