Needle Flame Test Analysis with a Needle Flame Tester

The flame test is one of the commonly used methods to evaluate the fire danger of electrical and electronic products. GB/T 5169.5-2020 “Test Fire Five – Test Flame Needle Flame Test Method Equipment, Confirm Test Method and Guide” as the latest version of the standard, after four revisions, clearly defines the purpose of the test is to determine that under the specified conditions, the test flame will not cause the component to ignite, or the test flame ignites the combustible component, but the burning time or burning length of the component is limited, and the flame or The burning or hot particles falling from the sample will not spread the combustion.

The test flame applied to the sample simulates the flame that may be generated from the components near the sample in actual application, such as the flame generated due to electrical failure. The standard continuously refines and improves the requirements in terms of test conditions, test methods, test equipment, and calibration standards, and the detection capabilities of the laboratory are continuously improved, the consistency between laboratories is obviously improved, and the satisfaction rate of the ability verification results is stable at about 90%.

In recent years, the capacity verification results report has been analyzed from many aspects such as fume hood, floor laying, air source, flame confirmation, fire time, pre-treatment, test environment, equipment calibration, test operation, etc., which help the laboratory to analyze the problem of dissatisfaction. All of the above analyzes are based on the existing standard requirements. With the strengthening of the ability verification program planning in recent years, the same batch of samples are tested from the two aspects of tolerance and intolerance by a needle flame tester at the same time, and the satisfaction rate of the two results is significantly different, about 25% (that is, the satisfaction rate of the result being tolerant is about 90%, and the satisfaction rate of the result being intolerant is about 65%).

Through the classification and statistics of the flame “removal” method at the end of the fire time, the dissatisfaction rate of the results is much higher than other methods when the flame removal method is suddenly extinguished, exceeding 50%. Due to the number of laboratories that use this flame removal method accounting for more than half of the laboratories participating in the experiment, the dissatisfaction rate of the results is much lower than the satisfaction rate of the results being tolerated.

Needle Flame Test

At present, more than half of the laboratories in China use the needle flame tester with the sudden flame extinguishing method to “remove” the flame, and the statistics show that at least 25% of the laboratories in China have the risk of this material being mistaken for qualified and being applied to non-metallic components with higher levels of requirements. The risk of inadequate flame resistance performance of the product entering the market, thereby posing a great threat to the safety of people’s property. For example, when the fire time is 30 s, materials with ignition time from 20 s to 30 s and continuous combustion have the possibility of this risk, and the closer the ignition time is to 30 s, the higher the risk. Therefore, in the absence of relevant standards, calibration specifications and other constraints, how to evaluate the possibility and severity of the risk and what measures should be taken to address it will ultimately be borne by the testing agency.

Risk Control
GB/T 5169.5 and other IEC standards adopt “manual removal of flame” as the igniting test device currently used in the international market, without differences due to the difference of flame “removal”. In China, due to the high degree of automation of the test devices and various flame “removal” methods, the differences are greater, which directly affects the electrical safety and the impact is wider. As there are no corresponding confirmation requirements in the standards and calibration specifications, the laboratory can not evaluate the influence of the flame “removal” method on the results at present. With the rapid development of non-metallic materials, more and more edge materials appear.

Therefore, it is necessary for the standard-setting organizations and calibration organizations to investigate and assess the risks, and to quickly increase the relevant requirements, regulate the flame “removal” method of domestic igniting test devices to control the risk from the source. The control valve is the core component of the test device, and the good or bad directly affects the performance of the whole test device. If only the Chinese-made igniting test devices are counted, the risk ratio of misjudgment caused by sudden extinguishing of the flame will be higher. In the absence of standards, manufacturers should first try to avoid using the sudden flame “removal” mode. Secondly, if manufacturers adopt the sudden flame extinguishing method, they should add factory needle flame tester for the test device before leaving the factory, and check the influence of its functions on the results.

At present, materials with ignition time of about 25s or higher and continuous burning can be identified. From the statistical results of capacity verification, it can be seen that the test results of the same type of test devices by different test organizations are basically consistent, while the results of different types of test devices from the same manufacturer are different, which shows that the control of components is essential. Manufacturers should strengthen the inspection of core components upon arrival, strictly control their parameters, and increase the inspection of the test device before leaving the factory to reduce the risks caused by the test device itself. As the ultimate users of standards and equipment, in case of inadequate prevention and control measures, the risks will be more compounded and magnified. In order to reduce the risks bring, how the test organizations respond will directly affect the quality of the tested objects, and unfavorable response will increase the risk of significant non-compliance greatly.

First of all, the test organizations should avoid purchasing test devices with this function as far as possible; if they are purchased, they should increase the acceptance criteria for sudden extinguishing in the purchasing and acceptance documents, evaluate the risks to confirm the impact of this function on the test results. Secondly, test organizations should strengthen personnel technology training and improve the operational capacity of test personnel. Some needle flame tester can choose automatic or manual mode. When testing, try to avoid using the automatic function. If it cannot be avoided, relevant confirmation methods and standards should be formulated, confirmed and recorded regularly, and the impact of serious non-compliance can be evaluated when risks occur. In addition, the test organizations can purchase various measures according to the specific situation of the test device, such as: the burner can only extinguish flame when the sooting time is reached, and the test personnel can lengthen the set sooting time, manually remove the test sample when the required sooting time is reached, which has higher requirements for personnel operation and protection.

All in all, test organizations generally prefer these igniting test devices, mainly because of their high degree of automation, low requirements for personnel ability, and the ability to avoid the influence of thermal radiation on the results caused by slow flame. Clause 5.3 of the requirements for flame in the standard stipulates that the flame of the required height can be reached by adjusting the gas flow rate, waiting for at least 5 minutes and making the burner reach the equilibrium state.

Generally speaking, flame should be stable for at least 5 minutes before test every time, and this way of extinguishing flame can not increase the efficiency of Needle Flame Test. On the other hand, thermal radiation may misjudge qualified materials as unqualified materials, thus replacing materials with better burning performance, which improves the flame retardant performance of the product. However, the sudden extinguishing of flame may misjudge unqualified materials as qualified materials, and be used in parts with higher flame retardant performance, thus causing products which do not meet the flame retardant performance requirements to enter the market, and the influence is extensive and the consequences are more serious. If the two can not be taken into account, the scheme with less influence should be selected to reduce the risk of the test organization and the safety risk of the product.

In conclusion
This paper presents the potential risks associated with the Needle Flame Test, providing in-depth analysis of the risks arising from the “removal” of flames, proving the widespread existence and severity of the risk. However, there are currently no control measures taken to address this risk domestically or internationally. It is hoped that this paper can draw the attention of relevant authorities to formulate unified control measures as quickly as possible, so as to reduce the risk and ensure the safety of the product.