Atmospheric hazard classifications

It is recognized, as a practical matter, that some substances may react slowly with atmospheric gases, e.g. oxygen, carbon dioxide, water vapour, to form different substances or they may react very slowly with other ingredient substances of a mixture to form different substances or they may self-polymerise to form oligomers or polymers. However, the concentrations of different substances produced by such reactions are typically considered to be sufficiently low that they do not affect the hazard classification of the mixture. 

There are minimum procedures for atmospheric testing that employers are required to perform to adequately assess the atmospheric conditions which exist in a confined space. This information is vital to the identification of atmospheric hazards within the space, and is also needed to make accurate determinations for later classification of the space. 

The relevant standards have been affected by the standard harmonisation process within the EU through the European Committee for Electrotechnical Standardisation (CENELEC) and through the International Electrotechnical Commission (lEC). Individual parts of BS EN 60079 deal with different aspects concerning electric apparatus for potentially explosive gas atmospheres, namely classification of hazardous areas, electrical installations in hazardous areas (other than mines) and inspection and maintenance of electrical installations in hazardous areas (other than mines). BS 50014 covers general requirements. 

According to European parliament regulation 1005/2009, the use of any solvent with the H420 (harms public health and the environment by destroying ozone in the upper atmosphere) hazard phrase in the Globally Harmonized System (GHS) of Classification and Labelling of Chemicals is severely restricted. 

Electrical apparatus for explosive gas atmospheres Classification of hazardous areas 5572/1994 BS EN 60079-10/1996 ... 

FPN No. 1) As a guide in determining when flammable gases are present continuously, for long periods, or under normal conditions, refer to. Recommended Practice for Classification of Locations for Electrical Installations of Petroleum Facilities, API RP 500-1991, Electrical Apparatus for Explosive Gas Atmospheres, Classifications of Hazardous Areas, lEC 79-10 and. Institute of Petroleum Area Classification Code for Petroleum Installations, IP 15. 

Hazardous places are classified in terms of zones (divisions) on the basis of the frequency and duration of the occurrence of an explosive atmosphere (IEC 60079-10 200X, Classification of Hazardous Areas European Standard EN 50281-3 200X, Classification of Areas Where Combustible Dusts Are or May Be Present ). 

Thus, for purposes of waste classification, it appears possible to assess the risk from the intrusion and atmospheric release pathways at a generic hazardous waste disposal site. However, a generic assessment of risk from the water release pathway normally would incorporate assumptions that would be extremely conservative for many sites (e.g., the amount of water infiltration and travel times of hazardous substances to a nearby well). 

An example of a two-zone concept for areas hazardous due to combustible substances is given in Table 2.2. It shows the traditional classification (in the USA and Canada) into classes and divisions according to the probability of forming an explosive atmosphere. 

Various types of hazardous atmospheres are classified to make it easier to discern the specific equipment needed to work in a given hazardous atmosphere. Most manufacturers use these classifications in their operating specifications. This classification system is clearly laid out in NFPA 497 and should be studied to get an understanding of the system. The most common classifications are Class, Division, Group, and Zone. 

The process of evaluating the likelihood of forming flammable atmospheres in plant areas is commonly referred to hazardous area classifications (HAG). HAG is usually conducted in accordance with regulations, codes, and standards such as the NEG/NFPA and NFPA NEG/NFPA 70 classifies... 

After the localization of places and areas with the possibility of a formation of an explosible atmosphere, the resulting hazard must be assessed. Corresponding to the probability of formation of an explosible atmosphere, which represents the endanger-ment, these localized areas are attributed zones . Within a building the boundaries of a zone are defined at concrete walls. The zone classification still in use in Germany was first published by the BG-Chemie. Some changes to this system are to be expected... 

The sense of smell can sometimes be of use in ascertaining that the TLV of a hazardous substance has been exceeded before it is too late. J.E. Amoore and E. Hautala (Journal of Applied ToxicologyS, No. 6 (1983) 272ff) have developed an Odor Safety Factor classification with five categories the have also compiled a list of mean odor limits for 214 volatile substances based on various sources. These limits indicate the atmospheric concentration at which 50% of the test subjects, having been given prior warning, were just able to identify the odor. 

International Electrotechnical Commission [lEC] 2006 lEC 60079-10, Electrical apparatus for explosive gas atmospheres -Part 10 Classification of Hazardous Areas. 

The basic purpose of any respirator is, simply, to protect the respiratory system from inhalation of hazardous atmospheres. Respirators provide protection either by removing contaminants from the air before it is inhaled or by supplying an independent source of respirable air. The principal classifications of respirator types are based on these categories. 

Zone systems are followed in area classification by ATEX and lEC, and even NFPA has included zone systems of classification in their standard. The zone classification system probably has the edge over the class/division system because many consider the zone classification system to be more flexible and safer in hazardous locations. However, zone systems do not take care of the consequence of release. In case the consequences are important, as per the advice of the HSE.UK, it is better to go for a more conservative equipment selection. Although not officially accepted yet, various sources have tried to place time limits on these zones. The most commonly used values are as shown in Table X/3.3.2-l based on probability and duration of explosive atmosphere. 

Among the ANSI standards is the National Electrical Code (NEC) which is directed at the elimination or control of electrical hazards. It defines the classification of areas according to the degree of hazard possibly foimd in the atmosphere and prescribes wiring methods, grounding, control, etc. These factors are important in motor selection. The NEC is a product of the National Fire Protection Association (NFPA). 

The first step in the selection of appropriate equipment will be the classification of the hazardous area from the viewpoint of the likelihood of a flammable atmosphere being present. Other considerations will include temperature class or ignition temperature of the gas or vapour involved and external influences. A nurnber of different safeguards may be employed in the design and construction of the equipment to minimise the risk of ignition. Equipment is normally certified for use in a particular situation and marked accordingly. 

Where there are flammable materials that constitute an explosion risk, the locations in which the explosion risk exists are called hazardous areas. These areas are classified into zones according to the extent of the risk, using guidance published in BS EN 60079-10 1996 Electrical apparatus for explosive gas atmospheres. Part 10 Classification of hazardous areas. The zones are also defined in the European Directive on minimum requirements for improving the safety and health protection of workers potentially at risk from explosive atmospheres. The zones are ... 

Employers in control of hazardous areas need to determine the locations and extents of these zones in each of the hazardous areas, an exercise known as hazardous area classification. At present, in 2001, there is no specific legal duty to carry out hazardous area classification, apart from the general duties to carry out risk assessments and, in the context of mines, in Regulation 19 of the Electricity at Work Regulations. However, the Protection of Workers Potentially at Risk from Explosive Atmospheres Regulations expected to be enacted soon, will contain specific provisions relating to area classification and the need to record the area classification information in an explosion protection document. 

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