Hazardous Area Classification Rating

Since detectors are by definition exposed to combustible gases they should be rated for electrically classified areas, such as Class I, Division I or 2, the specific gas groups (normally groups C and D), and temperature ratings. It should be noted the UL presently does not specifically test combustible gas detector sensor heads for use in classified areas, although they do tests enclosures for control and data acquisition circuits. Several other international standards do evaluate combustible gas detectors for use in classified areas (e.g., BS 6020). 

---

Suitability for area - IP rating, GMP suitability, hazardous area classification. ... 

The design of electrical equipment and instrumentation is based on the nature of the process hazards or specific process classifications. The classification method is defined in the National Electrical Code it is a function of the nature and degree of the process hazards within a particular area. The rating method includes Classes I, II, and III, Groups A-G, and Divisions... 

Fusible Link a mechanical release device actiwited by the heat effects of a fire. It usually consist of two pieces of metal joined by a low melting solder. Fusible links are manufactured as various incremental temperature ratings and are subjected to varying normal maximum tension. When installed and the fixed temperature is reached, the solder melts and the two metal parts separate, initiating the desired actions Hazard Analysis the systematic identification of chemical or physical characteristics and/ or processing conditions and/or operating conditions that could lead to undesired events Hazardous Area, Electrical a US classification for an area in which explosive gas/air mixtures are, or may be expected to be, present in quantities such as to require special precautions for the construction and use of electrical apparatus HAZOP an acronym for Hazard and Operability study, which is a qualitative process risk analysis tool used to identify hazards and evaluate if suitable protective arrangements are in place if the process were not to perform as intended and unexpected consequences were to result... 

Figure 2.1 Classification of an area hazardous due to combustible gases/liquids into zones 0, 1 and 2 [50], The value R is tabulated in Table 2.4 as a function of the filling rate into the tank (liquid with a Hash point <35°C). Dimensions given in metres.

A typical overall lag is 10 to 20 minutes, and it is not unusual to find a 30-minute lag or higher. It has been recommended (258, 309, 332,422) to restrict the sample transfer lag to less than 1 minute, and the sample interval to less than 2 minutes. In many situations, these targets are not readily achievable. Because of limitations associated with the electrical classification of the analyzer and the hazard rating of the area, and in order to ease maintenance, analyzers frequently need to be mounted in a protected shed, a fair distance from the column. The time it takes the samples to travel the distance can easily exceed 1 minute, even with high-velocity samples. 

---