Is intrinsically safe instrumentation rated higher in protection level than flameproof instrumentation?
Intrinsically safe and flameproof are distinct explosion-proof types. Intrinsically safe is further classified into three protection levels—ia, ib, and ic—and each corresponds to a different EPL category. For example, the intrinsically safe ic level offers a lower degree of protection than the flameproof d level, whereas the intrinsically safe ia level provides a higher degree of protection than the flameproof d level. (See the table “Correspondence Between Explosion-Proof Types and EPL Categories” for details.)
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“Correspondence Between Explosion-Proof Types and EPLs”
Therefore, intrinsically safe and flameproof explosion-proof technologies each have their own characteristics and advantages, making them suitable for different products and applications.
Can intrinsically safe instruments replace flameproof instruments?
In practical terms, there are many types of explosion-proof technologies. Among instrument and equipment applications, intrinsically safe explosion protection and flameproof explosion protection are widely used due to their high safety and ease of operation.
Definition of intrinsically safe “i”:
An explosion-proof type of electrical equipment that limits the energy of electrical sparks or thermal effects that may be generated by equipment internal components and continuous conductors exposed to explosive atmospheres to a level that cannot cause ignition.
Intrinsically safe explosion-proof technology is a “safety-by-design” approach that prevents explosions by limiting the energy of ignition sources. The fundamental principle is to limit the energy of ignition sources so that, even in the event of a specified fault, explosive substances in an explosive atmosphere will not be ignited. Equipment is required to ensure that the electrical sparks and thermal effects that may occur under both normal operating conditions and fault conditions are respectively below the minimum ignition energy and the auto-ignition temperature of the hazardous explosive gases. Intrinsically safe technology is a low-power design approach; as such, it offers numerous advantages, including simple construction, compact size, light weight, the ability to perform maintenance and replacement while energized, high safety and reliability, and broad applicability.
Definition of explosion-proof type “d”:
An explosion-proof type of electrical equipment in which the enclosure is capable of withstanding an internal explosion of an explosive mixture that has entered the enclosure through any joint surface or structural gap, without sustaining damage, and without causing ignition of the external explosive gas atmosphere composed of one or more gases or vapors.
Explosion-proof isolation technology primarily involves isolating ignition sources while allowing hazardous gases to enter the explosion-proof enclosure, where an explosion may occur inside the enclosure.
The enclosure must have sufficient mechanical strength, and the mating surfaces of all enclosures must feature adequate engagement length and minimal gaps to prevent internal explosions from propagating through the flameproof joints and triggering an external explosion. This approach falls under gap-type explosion protection, relying on the presence of gaps and sufficient engagement length to achieve cooling and flame extinction.
As a general rule, higher-EPL equipment may substitute for lower-EPL equipment, or equipment of the same EPL category may be substituted; however, when making such substitutions, it is essential to ensure compliance with the requirements of the respective explosion-proof types.
Which is more commonly used in chemical plants: intrinsically safe instruments or flameproof instruments?
When troubleshooting instrument faults, live maintenance in hazardous (explosion-proof) areas may be necessary (as most repairs require power-on operation, and some faults cannot be diagnosed without power). Intrinsically safe instruments permit live opening of the enclosure for maintenance, even if a cable short circuit occurs; in contrast, flameproof instruments generally do not allow live opening of the enclosure, and such live maintenance requires additional safety measures.
From a pricing perspective, for small instruments with high usage volumes—such as explosion-proof and intrinsically safe transmitters for temperature and pressure, as well as valve positioners—their prices are roughly comparable. However, intrinsically safe instruments require the addition of a safety barrier, which typically costs between several hundred and about one thousand yuan, resulting in an overall price that is slightly higher than that of flameproof instruments.
Taking into account factors such as ease of maintenance, safety, engineering consistency, and cost, process units in chemical plants typically prioritize intrinsically safe instruments (Class ia) in the process area, while utility areas generally standardize on explosion-proof instruments.
Why are intrinsically safe instruments so complex? Why not just go with explosion-proof ones across the board?
(1) Classification of Hazardous Areas in Explosive Gas Atmospheres
Due to the varying conditions at the production site, According to the current GB 50058-2014, hazardous areas in explosive gas atmospheres are classified as Zone 0, Zone 1, and Zone 2.
Zone 0: An environment in which explosive gas mixtures are continuously present or exist for long periods of time;
Zone 1: An area in which an explosive gas mixture is likely to occur under normal conditions;
Zone 2: Under normal conditions, explosive gas mixtures are unlikely to occur, or if they do, they exist only for a short period of time.
(2) Classification of Explosive Substances and Corresponding Electrical Equipment Classification (Applicable Only to Gases)
(1) Class I: Intended for use in coal mine methane gas environments.
(2) Category II: Intended for use in explosive gas atmospheres other than coal-mine methane.
Based on the maximum experimental safety gap (MESG) or the minimum ignition current ratio (MICR), they are further classified into IIA, IIB, and IIC. IIA—representative gas: propane. IIB—representative gas: ethylene. IIC—representative gas: hydrogen.
(3) Ignition Temperature Classes for Explosive Gas Mixtures
(4) Equipment Protection Level EPL
According to the classification of hazardous locations, the relationship between explosion-proof zones and the applicable equipment protection level (EPL) is as follows:
Ga level: Equipment for use in explosive gas atmospheres, with a “very high” level of protection, is not a source of ignition under normal operation, during the occurrence of expected faults, or during rare faults.
GB level: Equipment for use in explosive gas atmospheres, with a “high” protection level, is not an ignition source under normal operating conditions or under anticipated fault conditions.
Grade Gc: Equipment for use in explosive gas atmospheres with a “general” protection level, which is not a source of ignition under normal operating conditions, may nevertheless be equipped with additional protective measures to ensure that, even when ignition sources are expected to occur frequently (such as lamp failures), no effective ignition will result.
The current GB 3836 series of standards and GB 50058 both introduce the concept of equipment protection level (EPL).
The EPL is a protection level assigned to equipment based on the likelihood of the equipment becoming an ignition source and the specific characteristics of explosive gas atmospheres, explosive dust atmospheres, and methane-explosive environments in coal mines.
(5) Correspondence between Certain Explosion-Proof Types and EPL
As referenced in the preceding section, “Correspondence Between Explosion-Proof Types and EPLs,” equipment rated at Ga level is sufficient for use in Zone 0 environments. The “ia” explosion-proof type remains an effective option for Zone 0 applications, but it is by no means the only one.
Class Ga is applicable to Zone 0, Zone 1, and Zone 2.
GB-level is applicable to Zone 1 and Zone 2.
Class Gc is applicable to Zone 2.
In summary, Intrinsically safe and flameproof are distinct explosion-proof types, each with its own characteristics and advantages, and are suited to different products and applications. The selection should be based on a comprehensive assessment of factors such as the feasibility of implementation, the operating environment, cost-effectiveness, and ease of operation and maintenance.
Further reading: Why is explosion-proofing necessary?
According to statistical data, approximately two-thirds of underground coal mine workplaces contain explosive substances; in the chemical industry, more than 80% of production workshop areas harbor explosive substances; and at oil extraction sites and refineries, 60% to 80% are classified as explosive hazardous locations.
An explosion is the sudden transformation of a substance from one state to another through physical or chemical changes, accompanied by the release of enormous amounts of energy.
The three essential elements of a chemical explosion are ： Explosive substances, oxidizers, and ignition sources.
Combustion promoter: such as oxygen in the air.
Ignition sources: Electrical equipment extensively used in the production process, as well as sparks generated by friction, mechanical wear, static electricity, and high-temperature hot surfaces.
Given that explosive substances and oxidizers are often unavoidable in production workshops, the primary focus of fire and explosion prevention is to eliminate or control ignition sources while simultaneously preventing the abnormal release of explosive materials.
Therefore, it is essential to implement appropriate explosion-proof measures for electrical measuring instruments.
