Active Standard: Standard Test Method for Temperature Calibration of Dynamic Mechanical Analyzers Using Thermal Lag

The measuring technique of the SBI (single burning item) test instrument is based on the observation that, in general, the heats of combustion per unit mass of oxygen consumed are approximately the same for most fuels commonly encountered in fires (Huggett [12]). The mass flow, together with the oxygen concentration in the extraction system, suffices to continuously calculate the amount of heat released. Some corrections can be introduced if CO ₂, CO and/or H ₂O are additionally measured.

1.2 Calculation procedure

1.2.1 Introduction

The main calculation procedures for obtaining the HRR and its derived parameters are summarized here for convenience. The formulas will be used in the following clauses and especially in the clause on uncertainty.

The calculations and procedures can be found in full detail in the SBI standard [1].

1.2.2 Synchronization of data

The measured data are synchronized making use of the dips and peaks that occur in the data due to the switch from ‘primary’ to ‘ main’ burner around t = 300 s, i.e. at the start of the thermal attack to the test specimen. Synchronization is necessary due to the delayed response of the oxygen and carbon dioxide analysers. The filters, long transport lines, the cooler, etc. in between the gas sample probe and the analyser unit, cause this shift in time.

After synchronization, all data are shifted so that the ‘main’ burner ignites – by definition – at time t = 300 s.

1.2.3 Heat output

1.2.3.1 Average heat release rate of the specimen (HRR _30s)

A first step in the calculation of the HRR contribution of the specimen is the calculation of the global HRR. The global HRR is constituted of the HRR contribution of both the specimen and the burner and is defined as

[Formula removed.]

where

φ ( t) The last two terms x _{a_O2} and [Formula removed.] express the amount of moles of oxygen, per unit volume, that have chemically reacted into some combustion gases. Multiplication with the volume flow gives the

amount of moles of oxygen that have reacted away. Finally this value is multiplied with the ‘Huggett’ factor. Huggett stated that regardless of the fuel burnt roughly a same amount of heat is released.

The volume flow of the exhaust system, normalized at 298 K, V _D298( t) is given by

[Formula removed.]

where

The oxygen depletion factor ϕ( t) is defined as

[Formula removed.]

where

The mole fraction of oxygen in ambient air, taking into account the moisture content, is given by

[Formula removed.]

where

Since we are interested in the HRR contribution of the specimen only, the HRR contribution of the burner should be subtracted. An estimate of the burner contribution HRR _burner( t) is taken as the HRR _total( t) during the base line period preceding the thermal attack to the specimen. A mass flow controller ensures an identical HRR through the burners before and after switching from primary to the main burner. The average HRR of the burner is calculated as the average HRR _total( t) during the base line period with the primary burner on (210 s ≤  t ≤ 270 s):

[Formula removed.]

where

HRR of the specimen

In general, the HRR of the specimen is taken as the global HRR, HRR _total( t), minus the average HRR of the burner, HRR _{av_burner}:

For t > 312 s:

[Formula removed.]

where:

During the switch from the primary to the main burner at the start of the exposure period, the total heat output of the two burners is less than HRR _{av_burner} (it takes some time for the gas to be directed from one burner to the other). Formula (24) gives negative values for HRR( t) for at most 12 s (burner switch response time). Such negative values and the value for t = 300 s are set to zero, as follows:

For t = 300 s:

[Formula removed.]

For 300 s <  t ≤ 312 s:

[Formula removed.]

where

Calculation of HRR _30s

In view of the calculation of the FIGRA index, the HRR data are smoothened with a ‘flat’ 30 s running average filter using 11 consecutive measurements:

[Formula removed.]

where

1.2.3.2 Calculation of THR(t) and THR _600s

The total heat release of the specimen THR( t) and the total heat release of the specimen in the first 600 s of the exposure period (300 s ≤  t ≤ 900 s), THR _600s, are calculated as follows:

[Formula removed.]

[Formula removed.]

whereby the factor 1 000 is introduced to convert the result from kJ into MJ and the factor 3 stands for the time interval in-between 2 consecutive measurements,

and where

1.2.3.3 Calculation of FIGRA _0.2MJ and FIGRA _0.4MJ (Fire growth rate indices)

The FIGRA is defined as the maximum of the ratio HRR _av( t)/( t − 300), multiplied by 1 000. The ratio is calculated only for that part of the exposure period in which the threshold levels for HRR _av and THR have been exceeded. If one or both threshold values are not exceeded during the exposure period, FIGRA is equal to zero. Two combinations of threshold values are used, resulting in FIGRA _0,2MJ and FIGRA _0,4MJ.

1. The average of HRR, HRR _av, used to calculate the FIGRA is equal to HRR _30s, with the exception of the first 12 s of the exposure period. For data points in the first 12 s, the average is taken only over the widest possible symmetrical range of data points within the exposure period:

   [Formula removed.]

   [Formula removed.]

   [Formula removed.]

   [Formula removed.]

   [Formula removed.]

   [Formula removed.]

2. Calculate FIGRA _0,2MJ for all t where:

   (HRR _av( t) > 3 kW) and (THR( t) > 0,2 MJ) and (300 s <  t ≤ 1 500 s);

   and calculate FIGRA _0,4MJ for all t where:

   (HRRav( t) > 3 kW) and (THR( t) > 0,4 MJ) and (300 s <  t ≤ 1 500 s);

   both using:

[Formula removed.]

where:

As a consequence, specimens with a HRR _av not exceeding 3 kW during the total test have FIGRA values FIGRA _0,2MJ and FIGRA _0,4MJ equal to zero. Specimens with a THR not exceeding 0,2 MJ over the total test period have a FIGRA _0,2MJ equal to zero and specimen with a THR not exceeding 0,4 MJ over the total test period have a FIGRA _0,4MJ equal to zero.

Withdrawn Standard: Test Method for Determination of Temperature of Deflection Under Load (Withdrawn 1998)

1.1 Validation of methods and apparatus is requested or required for quality initiatives or where results may be used for legal purposes.

1.2 This standard provides terminology relating to validating performance of thermal analysis methods and instrumentation. Terms that are generally understood or defined adequately in other readily available sources are not included.

1.3 The terminology described in this document is that of the validation process and may differ from that traditionally encountered in ASTM standards.

1.4 A definition is a single sentence with additional information included in a Discussion .

Keywords

Performance–laboratory instrumentation/process; Terminology–thermal analysis; Thermal analysis (TA); Validation;

ICS Code

ICS Number Code 01.040.17 (Metrology and measurement. Physical phenomena (Vocabularies)); 17.200.01 (Thermodynamics in general)

DOI: 10.1520/E2161-08 ASTM International is a member of CrossRef.

Citing ASTM Standards

[Back to Top]