What Is Intrinsic Safety?

Intrinsic safety refers to the function of making the production equipment or production system itself safe by design and other means, which will not cause an accident even in the event of misoperation or failure. Including fault-safety (misoperation will not cause accidents or prevent misoperation automatically), and fault-safety functions (equipment can be temporarily operated normally or the safety state is automatically changed when the equipment or process fails). The current relevant standards are GB 3836.18-2010 Explosive Environment Part 18: Intrinsically Safe System, GB 3836.1-2010 Explosive Environment Part 1: General Requirements for Equipment. "GB 3836.1-2000 Electrical equipment for explosive gas environment Part 1: General requirements" has been abolished and replaced by the 2010 edition. ^[1-3]

Intrinsically safe

The term intrinsic safety is derived from the GB3836.1-2000 standard. Intrinsically safe explosion-proof electrical appliances are one of the classifications of explosion-proof electrical equipment designed for use in coal mines. Explosion-proof appliances are generally divided into

The theoretical basis of intrinsic safety is to ensure that the electrical and thermal energy in the system are low enough not to cause explosive gases to burn, so only low voltages and small currents are allowed to flow in hazardous areas, and there are strict restrictions on energy storage.

The most common protection methods are to use multiple resistors in series to limit the current flowing (assuming that the resistor will open when it fails), or use multiple Zener diodes to connect to the site to limit the voltage (assuming that the diode will short circuit when it fails). Occasionally, and sometimes with electrical isolation. The certification regulations for intrinsic safety barriers require that these restricted components can maintain their certified voltage and current if they are damaged to a certain extent.

For example, a measurement device used in a hazardous area needs to be designed to operate under low voltage and low current, and it must not have a large capacitance or inductance to avoid sparks during discharge. The device must be connected to a non-hazardous area in a control panel with a safety barrier in accordance with a certified wiring method. The purpose of the safety barrier is to confirm that there is no accidental short circuit between the measurement circuit and the external power supply equipment. And the current still needs to be maintained within the voltage and current range required by the certification.

In normal use of equipment, tiny sparks can be generated by switches, motor brushes, connectors or other components. These sparks will ignite the surrounding flammable gas. The design principle of intrinsically safe equipment does not include any components that generate sparks. If there are energy storage components, their energy storage cannot be large enough to generate sparks. For example, when carrying flammable goods by sea, when the goods are transported between sea terminals, tankers or barges, two-way radio communication is required. If some unexpected events (such as spills of flammable goods) are stopped, transportation must be stopped. The US Coast Guard requires that two-way radios be certified for intrinsic safety.

Another concept related to intrinsic safety is to control the temperature of parts when they are abnormal. Under some specific faults (such as a semiconductor internal short circuit), the temperature will be much higher than the temperature of normal use. At this time, protection components such as current-limiting resistors or fuses need to be used to ensure that the component temperature will not reach a level that will cause the combustible gas to spontaneously ignite under any circumstances.

Except for properly designed battery-powered equipment, other field devices or wiring cannot be intrinsically safe by themselves. A properly designed intrinsically safe system is required to ensure its intrinsic safety. Such systems generally have detailed instructions to ensure their safe use and maintenance.

Terms related to intrinsic safety management ^[4]

Intrinsic safety is the pursuit of the safety, reliability, and harmonization of human, material, system, and system elements in the production process of an enterprise, so that various hazard factors are always under control, and then gradually approach the essential and permanent safety goals.

Intrinsic safety is an implementation form that cherishes life. Intrinsic safety is committed to systematic inquiry and essential improvement. Emphasis is on the system as a platform, through the complex phenomenon, to grasp the essential factors that affect the realization of safety goals, to pinpoint the "one hair" that can affect the whole body, and to outline, through no slackness in thinking, no gaps in management, and no hidden dangers in equipment The system is non-blocking, achieving zero quality defects and zero accidents.

Compared with the intrinsic safety of things, systems, and systems, human intrinsic safety has a prerequisite, guidance, and basic status.

Human intrinsic safety includes two basic meanings. One is that people essentially have a need for security. The second is that through education guidance and institutional constraints, people can achieve safe production of systems and individual posts without accidents.

Human intrinsic safety is a goal that can be approached continuously, and at the same time, it is a process consisting of specific small goals. Human intrinsic safety is not only the goal in the process, but also the process of many goals.

Intrinsically safe employees can be commonly explained as: want to be safe, be safe, and be safe. That is, with the concept of autonomous security, sufficient security skills, and reliable security

The intrinsically safe explosion-proof method is to use the safety barrier technology to limit the electric energy provided to the field instruments to a safe range that can neither generate enough sparks for detonation nor sufficient temperature rise for the surface of the detonated instruments, thereby eliminating the explosion-proof method of the detonation source.

For instrumentation and control loops, limiting energy first means limiting voltage and current. Capacitors and inductors also need to be limited because they can store and release electrical energy.

In practice, people use spark experimental devices to determine the electric energy limit parameters for different dangerous gas types through experiments. Commonly used electric energy detonation curves given in international standards and Chinese national standards include voltage and current detonation curves, voltage-capacitance detonation curves, and current inductance detonation curves. Based on these curves, and with reference to a factor of 1.5, one can determine the electrical energy limit parameters for a given circuit when a certain type of gas is involved.

For example, when a IIC gas (such as hydrogen) is involved, the voltage limit for a standard 24VDC power supply circuit (such as a transmitter, electrical converter, solenoid valve, etc.) is usually set to 28V. Check the voltage and current detonation curve according to this voltage limit value, and consider the insurance factor of 1.5 times to determine the current limit value at this time. It can be determined that the current limit value at this time should be 119mA. According to the 28V voltage limit value and considering the 1.5 times the insurance factor, check the voltage-capacitance detonation curve, it can be determined that the loop capacitance value should be limited to 0.13F. According to the 119mA current limit value and considering the 1.5 times the insurance factor, check the current inductance detonation curve, it can be determined that the loop inductance value should be limited to 2.55mH.

In order to limit the surface temperature of the instrument, in addition to limiting the open circuit voltage and short circuit current of the circuit, the maximum power of the circuit must also be limited.

Intrinsically safe explosion-proof circuits always consist of a combination of an intrinsically safe field instrument and a safety barrier as a circuit energy-limiting associated device </ CA>