Automation systems in hazardous and explosive areas require special products and engineering. The applications to be made in such regions are specified with relevant directives and standards. In the light of these standards and regulations, the dangers of automation systems are eliminated.
The explosion is the release reaction of the high energy that flammable substances perform together with oxygen suddenly. Flammable materials can be in the form of gas, vapor, smoke or dust.
An explosion can occur when all 3 conditions below are at the same time.
- Explosive substance (in sufficient quantity and concentration)
- Oxygen (from the air)
- Ignition source
An important parameter in safety-related observations is the flash point. The flash point determines the lowest temperature for explosives. External ignition may explode the vapor formed on the liquids (at normal air pressure). If the flash point is above the actual temperature, the explosion may not occur. The flash point may fall down if different liquids mix. In order to create an explosive atmosphere, the concentration of the explosive substance must be within the desired range. If there is too high concentration (rich mixture) or too low concentration (lean mixture) then the explosion may not occur; no permanent reaction or explosion reaction occurs. The mixture reacts only between the lower and upper limits.
EXPLOSION LIMITS DEPEND ON THE AMOUNT OF OXYGEN IN THE AIR FROM THE PRESSURE OF THE ENVIRONMENT.
Physical Basics and Definitions
1-Do not create an environment for potential explosion (Priority protection)
- Avoid flammable materials
- Make it stagnant (add nitrogen, carbon dioxide, etc.)
- Limit concentration by natural or technical ventilation
2-Protect from ignition effect
- Separate potentially explosive zones as dangerous zones
3-Limit the explosion effect (Structural protection)
- Use pressure-tight or shock-resistant construction
- Pressure relief or balancing equipment
- Suppression of explosion using extinguishing equipment
Automation Systems in Hazardous Areas
Europe ATEX (Atmosphère explosible)
Many guidelines and directives have been prepared worldwide and on a regional basis.
Harmonization and unification of national rules and directives have been implemented in Europe since 2001.
Directive 94/9 / EG (ATEX 95) Manufacturer Directives
- Determining the basics
- Security requirements
- Conformity assessment procedure
- Grouping and categorizing devices
- CE marking
- Directions for use
Directive 99/92 / EG (ATEX 137) Workspace Directives
- Explosion risk assessment
- Classification of the regions
- Work safety
- Employee training information classification
On a global basis, efforts are made to find a single guide and guideline for explosion protection.
International IECEx (International Electronical Commission)
- Implementation of European EN standards
- Accepted in Australia and China
USA NFPA 70 NEC (National Electrical Code)
- Articles defined in 500 and 505
- Partially similar to IEC
Kanada CEC (Canadian Electrical Code)
- Defined in Chapter 18 and Annex J
- Partially similar to IEC
Ignition Protection Types
The types of fire protection for electrical devices in hazardous areas for gas-based explosions are described in the image below.
Ignition protection types for electrical devices in areas with flammable dust are as follows.
Increased Security | IEC 60079-7
Safety is created by creating boxes to prevent the formation of electric arc or spark by preventing overheating.
level is increased, and sources that can create sparks inside the normal device are destroyed.
Terminals and junction boxes, control boxes must be Ex materials for assembly. Squirrel cage motors, lighting fixtures.
Flameproof enclosure | IEC 60079-1
Preventing the flame from leaking out
Indicators, control systems, motors, transformers, heating devices, lighting fixtures
Pressurized Housing | IEC 60079-2
The Basic Principle
Keeping excess pressure in a container
- Electric panels and control cabinets
- Large engines and analysis devices
px = Zone 1, 2 is also used.
py = Zone 1, 2 is also used.
pz = used in Zone 2
Internal Security | IEC 60079-11
The Basic Principle
Only parts with increased internal safety are used in explosive areas. If an electrical circuit or device has internal safety, it does not generate sparks and emit heat. It does not create an ignition effect in explosive areas.
- Measurement and control technology
- Field equipment, sensors, actuators
ia = Zone 0, 1, 2 is used.
ib = Zone 1, 2 is used.
ic = Zone 2 is used
Oil immersion | IEC 60079-6
Electrical equipment or parts are immersed in protection fluid. The aim is to prevent the spark from spreading out.
Powder Filling | IEC 60079-5
- The box of the electrical equipment is filled with dust. Thus the firing effect is suppressed.
- The spark formed on the surface is not carried inside or the ignition effect caused by overheating is prevented.
Sensors, electronic ballasts, transmitter
Coating | IEC 60079-18
The ignition effect of the parts placed in metal casting is prevented.
ma = Zone 0, 1, 2 is used
mb = Zone 1, 2 is used
Ignition Protection Type | IEC 60079-15
Electrical components do not create ignition effects. (under normal working conditions or defined working conditions)
All equipment used in Zone 2
nA = Spark-free equipment
nC = equipment and components
nR = Gas tight housing
nL = Energy limited equipment
Optical propagation | IEC 60079-28
Optical diffusion preventing devices.
Ex op is = safe optical emission (natural)
Ex op pr = Protected type optical radiation
Ex op sh = Locked protection