What is a machine guard?
A guard is a physical element that separates people from a hazardous area. It can be part of a machine’s structure or added as a specifically designed protective device. Depending on the risk, it can also help retain parts, fragments, or materials. Its function must be clearly defined, because an effective barrier to prevent contact does not necessarily contain projectiles.
In machine safety, guarding is part of a set of measures. The possibility of accessing the hazardous area from different positions and the exposure of people other than the operator must be considered. Visible guarding alone does not demonstrate that all access points are controlled or that its resistance is adequate.
Interlocking devices link the guard’s position to hazardous functions. If the hazard persists after a stop has been ordered, the need to lock the guard until a safe condition is reached should be assessed.
Fixed and movable guards
Fixed guards are held in position by a mechanism that prevents their removal as part of the normal work cycle. Movable guards can be opened or moved and may require associated devices to monitor operating conditions. The choice depends on the frequency and purpose of access, as well as the existing hazard.
Choosing only the most convenient or space-saving solution is not appropriate. Frequent access requiring the removal of a protective device can encourage unsafe practices if it has not been properly designed. The assessment should determine how to reconcile operational and maintenance needs with the required protection, using applicable standards and technical instructions.
Interlocking and locking of the guard
The interlock links the guard’s position to the machine’s hazardous functions. In certain cases, it may also be necessary to prevent its opening until the hazard has passed. These are distinct functions that must be selected based on stopping times, energy sources, and possible access.
The presence of a switch alone does not demonstrate that the safety function is correctly designed. The control system, foreseeable failures, and the possibility of overriding it must be considered. Specification and validation are the responsibility of qualified personnel. This sheet does not provide instructions for modifying or bypassing safety devices.
Selection and design criteria
The design must respond to the hazard, the environment, and the tasks. Strength, secure attachment, visibility, ergonomics, clearances, openings, and ease of cleaning and maintenance are all important factors. Dimensions and performance should not be improvised; they depend on technical criteria and a specific assessment. The safety barrier should also not introduce dangerous edges, new points of entrapment, or obstacles incompatible with safe evacuation.
It is helpful to consult with those who operate and maintain the equipment. Their difficulties may reveal unforeseen access points, areas that cannot be observed, or operations that the design has not addressed. Incorporating this information during the selection process allows problems to be corrected before they become common reasons for removing or disabling the protection.
Use, opening and interventions
The work procedure must explain which access points are permitted, under what conditions, and for whom. Opening a protective cover may stop a function, but it does not necessarily mean that all energy sources have been isolated. Intervention tasks must be planned with the appropriate measures in place.
The emergency stop serves a complementary function and does not replace the necessary safety measures. Similarly, a warning or instruction to keep hands away does not substitute for the required protection against the risk of entrapment. The organization must ensure that the technical solutions are usable in actual work situations.
Practical example
A movable guard allows the process to be observed, but its surface gets dirty, requiring it to be opened repeatedly to check the product. This problem causes interruptions, and some people try to work with the guard open. A response limited to penalizing this behavior does not address the need for observation that the machine presents.
The technical review examines how to maintain visibility and cleanliness without exposure, along with the associated safety features. The results are then verified using various products and usage conditions. This example demonstrates the importance of addressing the causes of guard bypassing without accepting removal of the guard as a valid solution.
Inspection, maintenance and modifications
The inspection of work equipment must check guards to an extent proportionate to the risk. Relevant checks may include fixings, deformations, unforeseen openings, wear, and the operation of associated devices. Functional checks must be carried out safely and by competent personnel.
Modifications require technical assessment, documentation, and verification. Replacing materials, changing geometries, or relocating devices can alter performance even if the machine continues to produce. Traceability of all interventions must be maintained, and the conditions preventing continued use of the equipment until a defect is resolved must be established.
Reference framework and limits
In Spain, Royal Decree 1215/1997 establishes minimum requirements for equipment and moving parts, including guards or protective devices where applicable. Specific selection may also require technical standards and requirements for marketing or modifying the equipment. The applicable framework for each case must be verified.
A guard is not considered adequate simply because it is installed. Its effectiveness is demonstrated by its design, integration, condition, and use under the intended conditions. Preventive maintenance should combine documentation, observation of work practices, and technical checks, without converting a quick visual inspection into a complete safety validation.
