Current events

Opportunities for the Extinction of Fires in Live Equipment and Cable fires

Today, electricity is a prerequisite for development, and has become an integral part of everyday life. As a result of continued industrial development, new means and equipment are put into daily use.

Up-to-date systems of our days require continuous power supply not only in industry but also in everyday life. Let’s just take as an example the increasingly used solar collectors or the quick penetration of hybrid cars growing in popularity due to the energy crisis. However, de-energization (power shutdown) of equipment fitted with uninterruptible power supplies is not a simple task, and any ill-considered intervention may have serious consequences.

In industrial establishments, de-energization is a time-consuming procedure, if possible at all, for certain technological requirements to be met. Such circumstances may cause a delay in early intervention and result in damage to, or deterioration of, high-value equipment and systems. This may occasionally involve considerable financial losses not only in terms of the value and replacement costs of an equipment but also as regards the ensuing loss of production.

Electricity is one of the danger factors that may hinder fire fighters’ rapid intervention. Requirements for working on live equipment are set out in detail by various regulations; however, it should be self-evident to all that such regulations may need some updating and changes in view of the rate of technical development Hopefully, the new legislation of working on live equipment will be better suited to the requirements of our age and take into consideration the following aspects:

– Advantages of intervention with equipment under power:

• Extinction may start in an early phase of fire to prevent fire escalation.
• Early intervention may save human lives.
• Considerable damage to property can be prevented.
• Potential prevention of disaster situations in industrial establishments using dangerous technologies.

– Disadvantages of intervention with equipment under power:

• Only classified and certified means rated for the given voltage conditions may be used for the suppression of fires in live equipment.
• Only properly trained personnel well experienced in putting out fires in equipment concerned may be put into action as fire fighters.
• Minimum access and fire fighting distance requirements set for the electrical equipment concerned should be complied with during extinction of equipment fires.

– Classification of electrical equipment:

Electrical systems operating at AC voltages of 1,000 V or less and rated DC voltages of 1,500 V or less are called low-voltage, while systems operating at higher AC and DC voltages are called high-voltage systems by electrical safety professionals throughout the world. Also, these terms are stated on the warning plates designed for non-professionals. However, electricity providers also use, among themselves, the term medium-voltage for 1 to 35 kV systems as a distinction, and deem a system to be a “high-voltage” one only when it is over 35 kV. On the other hand, the term extra low-voltage is also used for consumer appliances, operating at AC voltages of 50 V or less and DC voltages of 120 V or less, that require special electrical safety in terms of shock protection.

– No-voltage condition:

The condition of any heavy-current electrical equipment (or a part thereof) where the equipment is disconnected from all possible sources of electricity, and all required operations, namely

• total disconnection,
• protection against switchback,
• checking of the no-voltage conditions,
• earthing and short-circuiting,
• barrier fencing around live equipment parts,
have been properly done. If any of the operations listed above has not been properly carried out, the equipment cannot be deemed to be in no-voltage condition.

– Biological effects of electricity:
Current limits (set for healthy males) according to publications by International Electrotechnical Commission (IEC):
(60 to 70% of current limits are considered valid for women and 50% for children.)

Since humans’ physiological capabilities are not quite the same, high dispersion of the experimental values is a matter of course. Therefore, it is more advisable to use the following (rounded) values in lieu of the above figures (that seem to be exact):

? Sensation threshold: 1 mA (no less amperage can be sensed).
? Release threshold: 10 mA (it is impossible to release the metal conductor grabbed over this limit).
? Danger of venticular fibrillation: 50 mA
These values have been set for alternating currents of industrial frequency (50 to 60 Hz) and adult males.

– Flashover distance:
Flashover distances “a” for high-voltage equipment according to Hungarian Standard
MSZ 1610-1:1970:

– Safety distance:
Decree No. 72/2003 (X. 29.) GKM on the Issue of the Safety Code for Working On Live Equipment.

Minimum safety distance for working on live equipment:

Extinction of fires in live equipment and intervention at fires near equipment under power are a major concern for Paks NPP Fire Service just like for other fire brigades in major industrial establishments of Hungary and for professional municipal fire departments (HÖT) with such electrical equipment and installations within their respective action zones. In reality, the rules provided for in the relevant legislation (Decree No. 1/2003 BM) cannot or can hardly be observed, and we had no information on the prescribed intervention distances backed by empirical experience. Consequently, we deemed it necessary to conduct a test series that would provide verifiable data for the creation of intervention criteria.
Our goal was to ensure that conditions for, and the rules of, safe work during the extinction of electric fires could be laid down as a result of the test series.

The first tests were performed at the Budapest site of VEIKI-VNL Electric
Large Laboratories Ltd., with financial support from Paks Nuclear Power Plant.

The test conditions and methods were identical with conditions for the testing of appliances used for the extinction of fires in live equipment as per Standard MSZ EN 3.

The test series had multiple goals, namely to

• check conformity of the extinguishing equipment used at NPP Fire Service,
• select equipment suitable for use as portable and mobile fire extinguishers (jet pipe),
• select the applicable extinguishing media,
• lay down an appropriate extinguishing technology (including the selection of proper jet stream patterns, safety distances and necessary protective equipment).

The initial tests were performed at a voltage level of 15 kV as a reference point for Power Plant’s own 6 kV in-house system. The primary goal of the tests was to determine the value of stray current “creeping” through the extinguishing jet. Compliance with the conformity threshold set out in Standard MSZ EN 3 was defined as a test criterion. No current higher than 0.5 mA was allowed to flow along the applied extinguishing jet. This value was defined as the conformity threshold for fire extinguishing appliances instead of the sensation threshold of 1 mA.
We tested our own jet pipes, jet pipes used in Western Europe, equipment for rapid intervention from NEPIRO, a pulse water cannon from IFEX and a foam generator from TURBEX.

The jet pipes were tested for a single jet stream pattern from 10 m, a long diffuse pattern from 6 m and a short diffuse pattern from 3 m, all at 6 bars. The appliance was considered OK when stray currents measured on the jet pipe did not exceed the permissible limit.
The tests were carried out from a distance of 3 m for IFEX pulse water cannon and 5 m for TURBEX foam generator (using a foam canvas).

While testing, we tried, as far as possible, to model real-life circumstances instead of ideal ones (“dry and safe place”), including tests performed in a wet place and under foggy and rainy weather conditions.
As a result of the test series, we have chosen 2 types of jet pipe producing the best test values. NEPIRO and IFEX equipment have been classified as “Compliant” ones, while the TURBEX foam generator has failed to be classified as “Compliant” for excess of the measurement range.

Additional tests were carried out in subsequent years, using the jet pipes already selected and made operational. Theoretical and practical training sessions were held two times a year for the entire early intervention personnel of NPP Fire Service. These advanced training events offered the intervention personnel an opportunity for gaining first-hand experience in extinguishing fires of live equipment as well as practising the setting of proper jet stream patterns and determining appropriate safety distances.

We invited the representatives of Tolna County Directorate for Disaster Management, Professional Municipal Fire Department of Paks and Rescue Organization Division of the National Directorate General for Disaster Management, Ministry of Internal Affairs (BM OKF) to attend our 2003 and 2004 exercises.

From the year 2004 on, the scope of our exercises has been extended to cover some more interesting experiments, including the cutting of underground cables.
For cable cutting, we use a purpose-designed insulated hydraulic cutting head, keeping an appropriate safety distance (8 m) and applying the specified earth conditions. First, we have cut cables with 400 V, and then 6 kV and 15 kV rated voltages. Cable cutting can offer a particularly useful solution in real fire situations emerging in cable spaces when there is no other way for de-energization because of the damaged or otherwise unidentifiable cables.
Cable cutting exercises are designed to provide an opportunity for the mental preparation of the early intervention personnel and to allow them to gain personal experience.

As a conclusion of the test series, we have tested and then procured personal protective equipment (protective gloves rated for a nominal voltage of max. 6 kV and isolation bars). Our test reports and a draft Fire Extinction Code were submitted for approval to Rescue Organization Division of BM OKF in autumn 2005.

In May 2006, BM OKF Director General inspected, with the inclusion of Legal and Legal Representation Division, and approved the use of the Code for a temporary period to ensure that Paks NPP rescue and fire protection capabilities were taken to a higher level.
On 1 August 2006, Regulations for Extinguishing Fires of Live Electric Equipment with a nominal voltage of 6 kV or less entered into force in Paks Nuclear Power Plant. This document provides a regulatory framework for safe and efficient intervention using up-to-date fire extinguishing means in order to allow quick and efficient response to electric equipment and cable fires.

As part of the continuous evolution of our test series, steps will be taken towards examination of the opportunities for extinguishing fires in equipment operating at a higher voltage level and for the development of protective equipment and fire extinguishing technologies.
We hope that the tests we have completed so far and their results will provide useful data for the overall development of Hungarian fire departments and brigades, for the safety of fire fighters’ work and for the preparation of updated fire codes and regulations.

Paks, 21 July 2011

by József Tóbi, training executive

Florian Press
oktober 2011