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Who guarantees the fibre is dead? Not whoever is opening it

7 min read

A diagonal beam of light cuts across wet asphalt to a flush manhole cover, at night, black and white photograph
The light lands where you would not expect it, even while the rest of the pit stays dark: the same logic as an automatic restart pulse.

A pit opened at two in the morning, a backbone down between two exchanges twelve kilometres apart. The technician climbs down, finds the closure and, before touching the fibre, plugs the connector into the power meter: zero dBm, optical silence. He starts prepping the splicer. Less than two minutes later the instrument reads power again — a short pulse, then zero once more. Nobody touched anything at the far end: on some equipment still in service, it is the line terminal itself that, at fixed intervals, tries to switch back on to see whether the link is back. The meter that a moment earlier seemed to say everything is off was not lying: it was only photographing an instant.

An event, not a condition

An optical link, under normal operation, is fully enclosed radiation. The risk does not come from a permanent condition but from a specific event, which ITU-T G.664 (Optical safety procedures and requirements for optical transmission systems, edition 10/2012, still in force) calls loss of continuity: “Any event which may cause hazardous optical power levels to be emitted from some point along the path of an optical transmission system. Common causes of loss of continuity of an optical link are a cable break, equipment failure, connector unplugging, etc.” — a cut cable, a fault, an unplugged connector: from that moment on, not before, safety depends on what the equipment at the far end does, not on how careful the person holding the fibre happens to be.

The numbers a specification almost never asks for

For equipment with discrete or Raman-pumped amplification — the same equipment covered by what we wrote on high-power optical maintenance — the Recommendation sets out a precise sequence for automatic power reduction (APR). On loss of continuity, power must fall below the hazard threshold within a defined time: “The power reduction to Hazard level 1M for restricted locations (or 3B in controlled locations) on all optical outputs within the impacted OTS shall be carried out within a certain time (with a maximum of 3 s) from the moment the continuity in the OTS is interrupted.” Three seconds at most, not as soon as convenient. Restart is not immediate: “the power above Hazard level 1M (or 3B in controlled locations) can be restored after 100 s has elapsed from the moment the loss of continuity has occurred” — a hundred seconds minimum, time enough for anyone working to move clear before power returns.

There is a third number, one the Recommendation still describes but no longer prescribes. Before confirmation of restoration over an optical auxiliary channel became the norm, restart on single-channel SDH systems relied on blind pulses: one at full operational power, lasting 1.75-2.25 seconds, repeated every 100-300 seconds — Table II.1 sets these figures — regardless of whether the fibre had actually been repaired. They existed to test for restoration, not to confirm it before firing. The text is blunt: that mechanism “is, however, no longer considered appropriate because of revised IEC safety requirements”, yet it remains, for historical compatibility, in an informative appendix — equipment built on that logic has been “widely deployed over the past years” and stays in service.

Who can disable the restart — and who, at the closure, cannot

The Recommendation treats disabling as an option, not a default: “A disabling of the restart mechanism might be desirable, for example to repair a broken fibre without being disturbed by premature restart attempts.” Being able to disable the restart, to repair a fibre without a premature attempt getting in the way, is a function the equipment must have — but it typically lives on a network management system or a terminal in the exchange, not in the pit. Whoever is holding the splicer, in most cases, has no way of knowing whether someone at the far end has actually inhibited the restart: all they know is what the meter reads at that instant, on the very run whose IEC 60825 hazard classes should already be on record in the specification.

What Italian law says, and to whom

Legislative decree 9 April 2008, no. 81, Title VIII, Chapter V (arts. 213-220) sets out the requirements on artificial optical radiation. Article 216, paragraph 2, letter a), requires the employer to assess «il livello, la gamma di lunghezze d’onda e la durata dell’esposizione a sorgenti artificiali di radiazioni ottiche» — precisely the duration G.664 measures in seconds. The law asks for the assessment; the technical Recommendation remains the only source that says how long that duration actually is.

Article 217, paragraph 1, letter c), goes beyond assessment: among the technical measures to reduce emission it lists «l’uso di dispositivi di sicurezza, schermatura o analoghi meccanismi di protezione della salute». An ALS or an APR procedure with automatic shutdown are, point for point, the safety device this clause refers to — but the law does not name the technical Recommendation, and the specifications we have seen do not name it in its place.

Whoever works on the fibre must be trained, under article 184, paragraph 1, letter f), «alle procedure di lavoro sicure per ridurre al minimo i rischi derivanti dall’esposizione» — a procedure specific to that splice, not a generic laser-safety course. Chapter V, for that matter, does not only punish the employer: article 220 sanctions the competent physician too — responsibility is spread across more than one role.

One point Chapter V alone does not settle, and it is the most common one on site: the fibre often belongs to one operator, the crew opening the closure to a different contractor. It is article 26 — outside Chapter V, but binding on every contracted-out job — that places on the commissioning party the duty to provide in writing «dettagliate informazioni sui rischi specifici esistenti nell’ambiente in cui sono destinati ad operare» (paragraph 1, letter b). If the far-end equipment’s ALS/APR regime is written down nowhere, that duty stays on paper.

What a specification can demand

A specification buying a fibre run, or maintenance work on an existing one, can demand in writing:

  1. the declared optical safety regime for the equipment at the far end — legacy pulsed ALS, or APR with an auxiliary channel — not just the Recommendation’s name;
  2. the actual timings: how long it takes to shut down after loss of continuity, how long it waits before restarting, whether it sends full-power pulses in the meantime;
  3. a written procedure for inhibiting the restart before opening, naming who activates it and who verifies the outcome — not a verbal understanding;
  4. the written information required under article 26 on the specific risk at that network point, whenever the crew opening the closure does not manage the equipment;
  5. documented training on the specific procedure, not a generic laser-safety course.

What it cannot demand is that the good sense of whoever opens the closure stand in for any of these five points: no amount of individual caution sees a pulse arriving every hundred seconds from twelve kilometres away.

The point

Complying, in this field, means the risk assessment document with the measures under articles 217 and 218, targeted training under article 184, health surveillance — duties that remain the employer’s, not ours to take over. Deciding means something else: demanding from the equipment, before signing the specification, a declaration of the shutdown and restart timings and proof that the restart can be disabled — because the safety of whoever opens the closure does not depend on them. That is the record we write before any work on a live network: the state of the run, who disabled what, and for how long. For a network that accumulates closures, equipment and suppliers over the years, together with CSIDIA, the group’s other company, the optical safety regime of every piece of equipment feeds into the same network map — not a fact to look up in a manual on the day of the job.

Commissioning work on a live run, or unsure what restart regime the far-end equipment uses? Talk to an engineer: the site visit is at no cost, and it is worth knowing before anyone opens a closure.

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