Why is it possible to "downgrade" a laser to a lower class?

Lasers always pose risks and dangers, so they are classified and labeled so that it is immediately understandable how high the danger is and how serious the damage is that can be suffered by using a particular laser module or device that makes use of a laser.

Depending on the class to which the laser belongs, appropriate precautions must be taken according to the dictates of the regulations governing its use.

If the laser is accessible, that is, it insists in the environment where people can access and thus come into contact with it, the nominal laser class of the laser module itself from which the beam arises always applies.

In practice, if, for example, a Class 3B laser module is used and the emitted laser beam enters the environment where people have access, the class of the laser is precisely 3B and all precautions to be taken and prescriptions to be observed will relate to that class.

However, if a laser module of Class 3B is used in such a way that it can no longer persist in the environment where people may come into contact with it, that is, in such a way that the laser beam is no longer accessible, here it is that, while the source module obviously remains to be Class 3B, the device in which it is used may be downgraded to a lower class, for example to Class 1.

In general then, it can be said that a laser source is classified according to its hazard when used as such free in the environment, but the devices in which it is used can be reclassified according to how the laser beam contained in them interacts with the surrounding environment in which people are present.

For example, a piece of machinery in which a laser is used can be classified as Class 1 even if the laser source is Class 4, this is only possible if the laser beam from the Class 4 source poses Class 1 laser radiation hazards outside the device where people have access to it and if the device itself cannot be easily tampered with or used in such a way that this stringent condition is waived.

How to proceed to declassify a laser?

As mentioned in order to reclassify a device, machine, and in general any type of system in which a laser is used, it is necessary to create an efficient and safe barrier that prevents the laser beam from coming into contact with people and causing accidents, for example preventing it from causing fire or the destruction of the device or parts of it, in particular the protections of the same, and finally causing damage and therefore possible more serious chain accidents causing damage to other objects if precisely the protections fail.

The laser barrier, also called laser tunnel is basically a shielding that will have to be adjusted according to the power and characteristics of the laser source, the laser barrier, or laser tunnel, will have to comply with the requirements of EN60825-4.

The laser therefore must be confined to a certain area and must not be able to reach the eyes and skin of people in the surrounding environment, likewise it must not be able to damage the laser tunnel itself and in general the device that contains it, that is, the system must be safe and prevent with certainty that the laser beam cannot under any condition escape beyond the limits specified by the standard.

How to make the laser tunnel and other due protections?

The laser tunnel (or laser barrier) shall be robust, not prone to decay, resistant to the possible stresses that the device is expected to undergo, shall be made in such a way that it cannot be altered, tampered with, or modified except by means of suitable tools and intentionally, i.e., that it cannot be removed, even partially if not intentionally and with such effort as to make clear the intention to tamper with the system.

The tunnel should be made of opaque, non-reflecting metal, e.g., sheet iron or aluminum, possibly painted black with products suitable for the case, it should be of adequate thickness for the case, e.g., a minimum of 1.5 mm for a low-power class 4 laser, i.e., in general it should be indefinitely resistant to the diffuse laser radiation to which it will be subjected.

The good realization of the laser tunnel is fundamental, however, other aspects must also necessarily be taken care of, if the device or machinery is equipped with doors, covers, compartments, inspection windows and in general any kind of accessory component that potentially allows access to areas where the laser radiation may exceed the so-called "LEA" (Accessible Emission Limit) according to which it will be reclassified, these will have to have certain characteristics that ensure that the safety conditions remain.

For example, doors and covers that can be opened normally by users in order to use the device will have to be equipped with switches that disconnect and block the power supply to the laser source module.

Lids and doors that, for example, must be able to be opened for maintenance will have to be closed by suitable means such that they cannot be easily opened except by specific means, for example, by screws or bolts with uncommon head and point of engagement.

If inspection windows are present these must be protected with filter barriers of adequate optical density (OD) that abate to levels not dangerous to people the direct, reflected or scattered laser radiation that insists on them. The filters used must be approved and certified.

Finally, it is also desirable to include in the device in a clearly visible location a warning light (or several lights if necessary) indicating when the laser source is energized and in the process of being emitted so that people at any given time can know that potential danger is present; this is especially important if the laser radiation is of the invisible type, e.g., infrared.

Conclusions

In essence then, it is not possible to reclassify the laser source itself, but it is possible to classify the machine, instrument, device that contains the laser source.

Depending on how the source is used, it is possible to classify the device in which the source is incorporated according to the actual risk and hazard due to the laser radiation escaping from the device itself. The dictates of the various reference standards for lasers, machines and optical filters must be observed, and optical filters must be approved and certified.

The advantage in following such guidelines, precautions and prescriptions consists first of all in preventing injuries and accidents, but also in the second order, no less interesting, there is an economic advantage by being able to avoid having to implement special and particular safety measures and procedures, having to appoint a laser safety technician (TSL), putting in place onerous work on the structures that house the machinery and devices involved, and having to employ highly specialized personnel.

NOTE: The information given here is purely informative popularized technical-scientific in nature; it may be inaccurate, incomplete, obsolete and not applicable in your country. Users should always refer to the current local legislation in force and current reference regulations, if necessary using specialized consultants.