Thermal fire detectors. Part I. A tangle of regulatory contradictions.

Thermal fire detectors. Part I. A tangle of regulatory contradictions.

Thermal fire detectors. Part I. A tangle of regulatory contradictions

Historically, the most common detectors in fire alarm systems worldwide were heat detectors. This was due to their simple design, ease of maintenance, and, most importantly, low cost. Such detectors used heat sensors based on widely known physical laws and regularities, such as the change in linear dimensions from temperature, Curie's law for ferromagnets, temperature dependences of the phase states of some materials, temperature dependences of the resistance of semiconductors, etc.

The choice of sensor type for a fire detector is determined primarily by the threshold response temperature and the response time of this element of the fire detector. GOST 26342 [1] defined these parameters of a heat fire detector as the designation parameters, in addition, this document identified a separate class of heat fire detectors — differential detectors.

Thus, in the section “Main parameters of fire detectors” for heat detectors, the numerical values ​​of the parameters were determined as follows:

“3.1.1. The nominal value of the temperature of the controlled environment that causes the detector to operate (the threshold temperature of operation) is selected from the following series: 50; 60; 70; 80; 90; 100; 120; 140; 160; 180; 200; 250° C. If necessary, permissible deviations of this parameter are established in standards and technical specifications for detectors of specific types.

3.1.2. The differential detector must operate when exposed to a rate of increase in the temperature of the controlled environment selected from the following range:
3; 5; 10; 20; 30°C/min, or when exposed to a step change in the temperature of the controlled environment selected from the following range: 30; 50; 100°C. Permissible deviations from the nominal value of a step change in the temperature of the controlled environment, if necessary, are established in standards and technical specifications for detectors of specific types.

3.1.3. The maximum value of the response time of heat detectors is selected from the following range: 5, 10; 30; 60; 90; 120 s. Permissible deviations of this
parameter, if necessary, are established in standards and technical conditions for detectors of specific types.»

After the collapse of the Soviet Union, the Russian Federation, Ukraine and the Republic of Belarus created their own regulatory documents defining the requirements for thermal fire detectors, respectively: NPB 85 2000 [2], DSTU EN 545: 2003 [3] and NPB 1032005 [4]. The prototype for these documents was the European standard from the EN 54 series, but if the Ukrainian state standard became an authentic translation of the corresponding part of the European document, then the Russian and Belarusian standards differ significantly from the prototype.

Depending on the controlled nature of the temperature change indicating the occurrence of a fire, the Russian NPB 85 distinguishes maximum, differential, maximum differential and differential characteristic TPI. Maximum TPI [5] generate a fire alarm when the ambient temperature exceeds the set threshold. Differential TPI are triggered when the rate of temperature increase exceeds the set threshold. Maximum differential TPI combine the functions of maximum and differential detectors. TPI with differential characteristic have a response temperature that depends on the rate of increase in ambient temperature.

Maximum, maximum differential and differential detectors depending on the temperature and response time are divided into ten classes: A1, A2, A3, B, C, D, E, F, G, H. Differential detectors are allocated a separate class and are assigned a special index R1.

Maximum differential detectors depending on the temperature class must be designated by combined indices, for example, A3 R1.

Detectors with differential characteristics are additionally assigned an index R, for example, BR. Quantitative characteristics for the temperature value (temperature increase rate) and the associated permissible response time range are given in NPB 85.

It should be noted that the minimum response temperature (for classes A1, A2) is 54° C, and not (50±2.5)° C, as prescribed by GOST 26342. And the response time for TPI of all temperature classes and types at a temperature rise rate of up to 30° C/min should not be less than 20 s.
Thus, TPI with an inertia of 5 or 10 seconds simply cannot exist in principle.

According to DSTU EN 545, all types of TPI can only be of eight classes: A1, A2, B, C, D, E, F or G. These classes are characterized by the following indicators:

¦ normal use temperature;
¦ maximum use temperature;
¦ minimum static response temperature;
¦ maximum static response temperature.

As you can see, there are no temperature classes A3 and H, but the existence of thermal detectors with additional indices R and S is allowed. Moreover, detectors with additional index R, according to the tabular values ​​of the parameters, fully correspond to detectors with differential characteristics according to Russian NPB 85. And detectors with additional index S are direct antipodes of detectors with index R, since they should not operate with rapid temperature changes, but not exceeding the maximum operating temperature.

Temperature detectors of class S are ideal for use in such rooms as boiler rooms and kitchens, which are characterized by high rates of temperature increase over a long period of time. But in the state standard of Ukraine, as well as in the European document, there are no names for different types of thermal detectors.

However, the names of the fire extinguishing agents are given in the standard NPB 103 of the Republic of Belarus. Clause 9 of this document states: OPS “By the method of determining fire factors, fire extinguishing agents are divided into classes in accordance with STB 11.16.01 and are designated in these Standards by the following capital Latin letters:

¦ maximum fire extinguishing agent – ​​“M”;
¦ difference fire extinguishing agent – ​​“R”;
¦ differential fire extinguishing agent – ​​“S”.

Each of the fire extinguishing agent classes by temperature or response time in these Standards is conditionally divided into 8 types with the assignment of one of the alphanumeric indexes: A1; A2; B; C; D, E; F; G”.

As we can see, the names and designations of the TPI with additional indexes in this document are original, although the temperature classes of the detectors fully comply with EN 545. A detailed analysis of the technical requirements shows that the tabular figures for the inertia of maximum detectors and detectors with the additional index «R» according to NPB103 comply with the technical requirements of point heat detectors of the corresponding classes A1; A2; B; C; D, E; F; G and A1R; A2R; BR; CR; DR; ER; FR and GR of the Ukrainian standard DSTU EN 545. But detectors with the index «S» in these standards have completely opposite technical properties.

A heat detector with the index «S» according to the Belarusian regulatory document has an inertia that depends only on the rate of temperature increase and does not depend on the temperature class of the detector, and such a detector does not have the parameter «static response temperature», which confirms only the differential nature of the parameters of such a detector. Thus, the main and significant difference between the Russian and Belarusian standards from European and Ukrainian documents is the preservation of differential detectors as a separate type, as if taking up the baton from the Soviet GOST 26342. According to the new Russian standard GOST R 53325 [6], point heat fire detectors are subdivided by the nature of the reaction to the monitored sign of fire in accordance with clause 4.1.1.4 into:

¦ maximum;
¦ differential;
¦ maximum — differential.

And according to clause 4.5.1.1 of the specified standard, maximum detectors, depending on the temperature class, are marked with the following symbols: A1; A2; A3, B; C; D, E; F; G, H.

As we can see, the new Russian standard retained additional temperature classes: A3 and H, but TPI with differential characteristics simply disappeared as a class. At the same time, purely differential detectors remained in the standard, which are already marked with the index «R», and not R1, as was provided for in NPB 85. But the existence of detectors with the marking «S» is not provided for in this document at all. It should be added that the parameters of maximum detectors of the corresponding classes according to the Russian GOST are somewhat different from the parameters of detectors of the corresponding classes according to the Belarusian NPB 103 and the Ukrainian DSTU EN 545.

The dependencies of the response temperature of maximum heat detectors of class A2 on the rate of temperature increase according to GOST R 53325 are shown in Figure 1.

The same dependencies according to NPB 103 and DSTU EN 545 are shown in Figure 2.

The Russian standard does not allow maximum detectors to trigger early at a temperature increase rate of more than 1° C per minute, i.e. until the ambient air temperature reaches the minimum static trigger temperature for the corresponding detector class – in this case 54° C.

These are the temperature dependencies provided for in the European standard for class S detectors, but according to clause 6.1 of EN 545, additional tests are provided for such detectors.

During the tests, the detector sample must be stabilized at the temperature specified in table 1.1 in accordance with the temperature class.

After stabilization, the sample must be moved in a time not exceeding 10 s into an air flow at a speed of 0.8 m/s (mass equivalent at 25° C) and with a temperature specified in Table 1.1. The sample must be in the air flow for at least 10 min, any response of the sample during this time or during the movement is recorded.

A detector of this class should not operate during these tests. In addition, a detector with the index «S» should be the most inertial among maximum heat detectors, since the lower limits of the response time for these detectors correspond to the minimum excess of the air flow temperature over the stabilization temperature by 29 ° C.

Thus, we see that maximum TPI according to Russian and Belarusian standards can have different basic technical parameters. Detectors with R indices have the same technical parameters, but are called differently.

Detectors with S indices according to the Belarusian standard have directly opposite technical parameters compared to detectors with the same marking, but according to the Ukrainian standard.

EN 545 does not include purely differential detectors as a class. After all, purely differential heat detectors have no right to exist because they do not allow detecting fires that develop very slowly.

It is probably impossible to find an object that requires only differential heat detectors for protection. The probability of a gradual fire development at most objects is very high, and this requires the use of the most differential heat detectors.

To summarize, it can be said that when using TPI, it is necessary to carefully study not only the passport data, but also the certificates of conformity in order to know what standards these products were certified by. I would like industry specialists to use a single terminology when discussing TPI, but this is a topic for a separate discussion.

_______________________________________

V. Bakanov
Chief Designer of Arton Private Enterprise,
I. Neplokhov
PhD, Technical Director of «CENTERSB»

LITERATURE
1. GOST 26342-84 «Means of security, fire and security and fire alarm systems. Types, main parameters and dimensions.»

2. NPB 85-2000 «Fire safety standards. Heat fire detectors. Technical requirements for fire safety. Test methods.»

3. DSTU EN 54-5: 2003 «Fire alarm systems. Part 5. Point heat fire detectors.»

4. NPB 103 — 2005 «Fire safety standards of the Republic of Belarus. Heat fire detectors. General technical requirements. Test methods.»

5. A. N. Chlenov «Modern thermal fire detectors: main characteristics and application features» //Security systems. —
2004. — 1. — P. 55.

6. GOST R 53325-2009 «Fire-fighting equipment. Technical means of fire automation. General technical requirements. Test methods».

Source: journal «Algorithm of security» No. 5, 2011