The national standard GB2811-2007 "Hard hat" (hereinafter referred to as the new standard) implemented since December 1, 2007 is a revision of the GB2811-1989 "Hard Hat" standard. The new standard has enhanced the technical performance of the helmet. Requirements, the overall requirements are more systematic and complete, and have achieved basic integration with developed countries and regions.

The implementation of the new standard has promoted the improvement of the quality of our hard hat products, and the awareness of producers and users has been strengthened. In order to understand this standard more accurately and in depth, the technical contents of the old and new standards are now compared and the technical indicators in the old and new standards are analyzed so that the standard can be better understood and implemented.

Comparison of old and new standards

In GB2811-2007 "Hardware", compared with the original helmet standards, from the classification to the technical requirements have made some additions and changes, see Table 1 for the comparison.

Analysis of Change Content of New Standard of Hard Hat

From the above table, it can be seen that the new national standards for safety helmets have made changes to the original standards in terms of classification, requirements for chin straps, strength, quality, helmet impact, and puncture performance.

1. Revision of helmet classification

In the new standard, the classification of hard hat T-class (special type) was cancelled by the original standard. The original standard specifies 5 special hard hats with different performances, namely T1 (with flame-retardant function) and T2 (with Compressive function), T3 (compressive, antistatic, flame retardant) T4 charged (with electrical insulation), T5 low temperature (with low temperature resistance), and with the development of modern industrial technology and product technology, people's The demand for protection has changed, and the combination of five types of fixed special technical performance can no longer meet the needs of modern industrial production. Therefore, the five types of fixed special types are eliminated in the new standard, and they are collectively classified as special performance and contain flame retardant properties. , anti-static properties, electrical insulation properties, compressive properties and low temperature resistance. Producers can combine five special properties to produce special-type helmets according to the needs of use, which greatly increases the applicability of helmets in modern industrial production, improves the protective function of helmets, and improves the safety helmets in operation. Workers' protective effect.

2. Lower jaw belt and strength

In the old standard, the requirement for the chin strap was divided into two types: a rear hoop lining and a back hoop lining. Since most of the helmet linings of the helmet were mainly cotton, the back of the cotton lining was behind the head. There is no adjustable elastic rear hoop, only the Department to bring a fixed helmet, but the strap will appear loose phenomenon, resulting in the helmet accidentally fall off when hit by falling objects, it is required that the chin strap should be "Y" type , play a role in fixing the helmet. The plastic cap liner has an adjustable cap hoop, which solves the problem that the cotton strap is not fixed securely. Therefore, the requirements for the chin strap are single. In this case, the chin strap is mainly used for auxiliary fixing.

With the renewal of product technology, ergonomics has been widely used in product design, which has greatly improved the fit and stability of helmets and heads. Now, helmets are mainly combined with chemical fiber tapes and plastic cap liners. It has better strength and guarantees the stability of wearing, while the cotton lining has gradually withdrawn from the market. Some advanced helmets in foreign countries also use the chin strap as optional components, so there is no requirement in the new helmet national standard. All helmets must be equipped with a chin strap, but only the size of the chin strap is specified. However, the head cap should be adjusted according to the applicable head size specified in the helmet logo. This is in line with international advanced standards. It does not require strict product styles under the premise of ensuring safety, which is conducive to the development and improvement of product technology.

After research and a large number of examples show that in the use of helmets, due to the strength of the chin strap is too large, in the event of a collision or crash may cause injury to the operator's neck, severe can cause suffocation, so the new standard will be The belt strength is controlled between 150N~250N to ensure the strength of the lower jaw belt, and at the same time, the lower jaw belt can be broken when necessary to protect the neck of the staff from injury.

In practical use, although the cap hoop improves the wearing stability of the helmet, the chin strap on the one hand can assist the cap hoop to enhance the wearing stability, and on the other hand, it can be more convenient to wear, even if the helmet accidentally falls off, the operator can Quickly wear it to ensure the timeliness of protection and avoid injury due to accidental removal of the helmet. In actual use, if the purchased helmet is equipped with a chin strap, each unit should be in accordance with the manufacturer's requirements and the product instruction manual to tie the chin strap. According to the characteristics of their own operating environment, enterprises can also decide whether to choose helmets with squatting belts and ask related users.

In summary, when the purchased helmet is equipped with a chin strap, the chin strap should be fastened to match the cap hoop to maintain the wearing stability.

3. The quality of the helmet

With the development of product production technology and materials, lightweight, high-strength materials are widely used in the production field. Safety helmets increasingly consider wearing comfort while ensuring safety. New materials are used in helmet manufacturing. The application of lightweight helmets to the development of lightweight, so in the new standard to reduce the quality of helmets, enhance wear comfort, play a guiding role in the direction of product development.

4. Impact absorption performance

The new and old impact absorption performance standards are basically the same at the pretreatment temperature, except that the original 35°C pretreatment is cancelled, because with the environmental changes, the temperature cannot be called a limit temperature, and the significance of the safety performance test has been lost. The new standard will change the original standard of water to water soaking, while increasing the ultraviolet radiation pretreatment, the provisions of the shell must not have fragments off. Changing to water soaking is better to examine the safety performance of a helmet under simulated rain and snow conditions. In actual use, the cap liner may be completely saturated with rain and snow. The watering treatment cannot simulate this situation well, so the water treatment will be changed. For flooding treatment. Ultraviolet irradiation pretreatment is to prevent manufacturers from using recycled materials in the production process to manufacture safety helmets. Due to the low price of recycled materials and the low purity and consistency of the materials themselves, their mechanical properties and durability are very poor. Some recycled materials helmets With a little effort, it can be crushed by hand, but after the ultraviolet irradiation treatment, the helmet made of recycled materials can hardly meet the requirements of the standard, thereby curbing the flow of inferior products to the market.

5. Puncture resistance

According to the old standard, puncture resistance tests only one of the most unfavorable conditions of the helmet material in the shock absorption performance test. After years of testing and actual investigation, it has been found that the impact absorption performance of the helmet is not only good Material related, at the same time with the hat lining material, hat shell and cap lining with the design of the relationship are related to the material of each top of the helmet more than one, the most unfavorable conditions for the material to determine the difficulty of a unified scale; In addition, through research found that a lot of security The case where the cap is penetrated by the object is not under the most unfavorable condition for the cap shell selected in the impact absorption test, so when the new standard is formulated, in order to ensure the safety performance of the safety cap, the pretreatment of the puncture resistance performance will be performed. The conditions were consistent with the pretreatment conditions of the shock absorption test, which further improved the detection of the helmet and further improved the safety and quality of the helmet.

6. Low temperature resistance

In the old standard, the helmet with the cold function was only subjected to the impact and puncture resistance test after -20°C pretreatment. Based on this, the new standard added the impact and puncture performance tests under high temperature and water immersion conditions. The impact and puncture performance of the new standard in high-temperature and water-drenched environments is a part of the basic technical performance of helmets, while the low-temperature-resistant performance is a special technical performance. The standard specifies that special-type helmets should have all the properties of ordinary helmets, namely special The technical performance is an additional technical performance based on the satisfaction of general technical performance. In practical use, it cannot exclude the presence of complex environments such as alternating hot and cold or rain and snow in low-temperature environments. Therefore, it is safe for low-temperature performance. The safety performance test of the cap should also be fully considered, so as to guarantee the applicability and safety of the safety helmet in a complicated environment.

What needs to be further explained is why the safety helmet with low temperature resistance performance should be tested for safety after high-temperature pretreatment at 50°C. At present, China's helmets containing low-temperature-resistant properties are almost always equipped with a thermal layer. The main methods of thermal insulation include internal thermal insulation and external thermal insulation. When the heat insulation layer of the helmet is in the form of external insulation, the shell, cap lining and headband of the safety helmet all play a role in the heat preservation layer. At this time, the safety helmet has substantially the same internal conditions as an ordinary safety helmet when working. That is, close to human body temperature, it should have the same protective performance as an ordinary helmet. Therefore, the safety helmet must be subjected to high-temperature conditions and safety protection after treatment. When the heat insulation layer of the helmet is in the form of internal heat preservation, the safety helmet is completely exposed in the atmospheric environment. At this time, the safety helmet shall perform the safety protection performance test after pretreatment of low temperature conditions, taking into account a certain safety factor, the high temperature pretreatment temperature is 50 °C, low-temperature pretreatment temperature is -20 °C, the lack of any kind of pretreatment conditions of the test, the evaluation of the protective performance of the helmet is not comprehensive.