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What is Part P of the Building Regulations? What is Part P of the Building Regulations? Since 2005, all electrical work in dwellings in England and Wales, whether carried out professionally or as DIY, must meet the requirements of Part P of the Building Regulations. Part P is in place to keep you and your family as safe as possible from electrical hazards, and applies to new domestic properties, as well as any alterations or additions to electrical installations in existing properties, including full or partial rewires. Who is responsible for making sure that electrical work in your home meets the requirements of Part P? By law, the homeowner or landlord must be able to prove that all electrical installation work on their property meets the requirements of Part P, or they will be committing a criminal offence. Local Authorities have the power to make homeowners or landlords remove or alter any work that does not meet the requirements of the Building Regulations. What electrical work is notifiable in England? Electrical work which requires notification differs between England and Wales. Additional changes were introduced to Part P in England in April 2013. This means that electrical work in a dwelling, or associated with its surroundings, is notifiable to a local building control body where it includes: circuit alteration or addition in a special location –  (Certain zones within a room containing a bath or shower, or a room containing a swimming pool or sauna heater.) installation of one or more new circuits installation of a replacement consumer unit (fuse box) rewire of all circuits partial rewire new full electrical installation (new build) What electrical work is notifiable in Wales? The following are examples of electrical installation work in a dwelling, or associated with its surroundings, that is notifiable to a Local Authority Building Control in Wales: In general: a complete new installation or rewire; or the replacement of a consumer unit (fusebox); or the installation of: a new circuit, whether at low voltage (typically 230 V) or extra-low voltage); a solar photovoltaic power supply; electric ceiling or floor heating; ­an electrical generator; ­power / control wiring for a central heating system In a special location*, the installation of: wiring/equipment for telephone or extra-low voltage communications, information technology, control or similar purposes a prefabricated equipment set and any associated leads with integral plug and socket connections (for example lighting) In a kitchen** or special location: extension of an existing circuit within a kitchen or special location Outside of the dwelling, the installation of: a supply to a detached garage, shed or other outbuilding a supply to an electric gate or pond pump garden lighting a socket-outlet * A special location is a room containing a bath or shower, swimming pool or a sauna heater** For Building Regulations purposes, a kitchen is a room or part of a room which contains a sink and food preparation facilities Categories

Useful Links Links we find of use: www.metoffice.gov.uk www.which.co.uk/energy/creating-an-energy-saving-home/guides/underfloor-heating-systems/electric-underfloor-heating/ www.therenewableenergycentre.co.uk www.energysavingtrust.org. www.gov.uk/government/uploads/system/uploads/attachment_data/file/421751/20131118_SFAProtectingyourfamilyhomeWinter.pdf www.ageuk.org.uk www.moneysavingexpert.com www.bafsa.org.uk www.tica-acad.co.uk www.electricalsafetyfirst.org.uk/guides-and-advice/around-the-home/ www.electricalsafetyfirst.org.uk/guides-and-advice/around-the-home/ www.electrical.theiet.org/wiring-regulations/ www.abi.org.uk www.cia.org.uk/Portals/0/Winterisation%20Nov%202011.pdf www.networkrail.co.uk/timetables-and-travel/delays-explained/snow-and-ice/ www.rspb.org.uk/forprofessionals/farming/advice/species.aspx www.rhs.org.uk/advice/profile?PID=159 www.nhs.uk/livewell/winterhealth/Pages/Winterhealthhome.aspx www.gov.uk/government/news/winter-weather-uk-government-response www.rspca-bristol.org.uk/uploads/documents/1329298413_WinterCareAdvice.pdf www.campingandcaravanningclub.co.uk/helpandadvice/technicalhelp/looking-after-your-unit/winter-care-for-caravans/ www.healthandsafetyatwork.com/hsw/winter-weather-ppe www.hse.gov.uk/logistics/slips-trips-bad-weather.htm www.cibse.org/ Categories

Trace Heating At HTUK we design and supply electric trace heating systems and temperature controlled applications. Trace heating cables and silicon heater mats can be designed for residential, commercial and industrial applications such as pipework, storage tanks/vessels, hoppers, scientific equipment, catering equipment, underfloor heating, transportation and many more. Trace Heating (or Heat Tracing, or Surface Heating) is the method of applying heat to a body, or to a product (liquid, powder, or gas) contained within a system (pipework, vessel or equipment) for storage or transportation, in order to avoid processing problems or difficulties. The main types of heating are Freeze protection, Process Maintenance and Raise and Maintain and the above heating types are used to provide any one of the three main applications above. Freeze Protection The  purpose of the heat tracing is to keep the pipe or equipment above the freezing point of the product you are protecting. Process Maintenance The purpose of this type of application is to keep the equipment at an elevated temperature, normally above the 5°C threshold mentioned above. Raise and Maintain In this application, the product needs to be brought up from a start temperature up to a desired final temperature over a specified period of time. Trace heating standards Electric heat tracing is governed by a number of International and National Standards covering Industrial (Safe) and Industrial (Hazardous) locations. A list of the most important standards, to which many of our products are approved, are shown in the table below. We design and supply equipment approved to all national and international  standards. The current Electric heat tracingstandards are: •  IEC62395 – Electric Heat Tracing for Safe Industrial locations •  IEC60079-30 – Electric Heat Tracing for Hazardous locations •  IEC6036-4 – Electric Underfloor Heating In addition to the base design review we provide all drawings and documentation required. Hazardous Area Application Design and equipment selection for use in hazardous areas will be influenced by:- •  the area classification •  the gas group •  the temperature classification and equipment selected providing an appropriate type of protection The international standards developed especially for electric heat tracing, •  IEC62395 – for Safe Industrial locations and IEC60079-30 for Hazardous locations. Area Classification The probability of explosive conditions being present is defined by zone classification •  Zone 0 may have explosive gas-air mixtures present continuously or for long periods. Heat tracing is rarely, if ever, used in Zone 0 areas. •  Zone 1 may have explosive gas-air mixtures present in normal operation. •  Zone 2 may have explosive gas-air mixtures present only under abnormal conditions. Gas Groups Gas groups relevant to heat tracing in hazardous locations are:- •  IIA – Acetone, benzene, butane, ethane, methane, propane, etc. •  IIB  – Ethylene, town gas etc. •  IIC – Acetylene, hydrogen Temperature Classification The maximum surface temperature of the heater must be kept below the auto ignition temperature of the explosive gas or vapour mixtures which could be present. The classifications are:- T-Class  Maximum admissible surface temp ?C T1 = 450 °C  440 °C T2 = 300 °C  290 °C T3 = 200 °C  195 °C T4 = 135 °C  130 °C T5 = 100 °C  95 °C T6 = 85 °C  80 °C Types of Protection As non-sparking devices, most heaters are likely to be approved to the concept ‘e’ – increased safety (EExe). Sparking devices such as thermostats or circuit breakers are most commonly approved to the concept ‘d’ – flameproof (EExd), although  concepts ‘i’ – intrinsic safety (EExi), and  ‘p’ – pressurised apparatus (EExp) are also sometimes appropriate. Sometimes, distribution boards and control panels can be located outside the hazardous area to avoid the need for the additional costly protection.   Heat Loss from a Pipe Basic considerations: All pipes/equipment that are above the ambient temperature will experience heat loss. Heat loss is the loss of heat to the environment. If no heating is applied to the pipe/equipment it will eventually equal the ambient temperature, at which point the heat loss will be zero. The heat loss can be delayed by the application of thermal insulation. However, over a period of time, without heating the equipment will eventually match that of the ambient. To keep equipment above the ambient, it is essential to add heatingand insulationto offset the heat loss. The basic formula to calculate heat loss from a pipe is as follows;                                Q =     2π x K x (Tp-Ta)+ sf                                                             ln(d2/d1) Where; Q       Heat Loss (Watts/m)          K       ‘k’-factor for the insulation at Mean Temperature Tm (W/m°K)          Tp     Process Temperature (°C) Ta     Ambient Temperature (°C)          d2     Outer diameter of insulation          d1     Inner diameter of insulation          sf       Safety Factor (typically an extra 10%) The above calculation is based on Fourier’s Law for heat loss. For example; Pipe Size               4”                         MMT                      20°CMin Ambient          -15°C                    Insulation Thickness       1.5”‘k’ factor                0.034 W/m°K (Fiberglass)          Q =    2 x Pi x 0.034 x (20 – -15) + 10%                =       7.4767  + 10% = 13.4 W/m + 10%                   ln((4”+ (2 x 1.5”)) / 4”)        ln(1.75)           Q = 14.7 W/m Categories

Temperature Control What types of temperature Controllers are available and How Do They Work? There are three basic types of controllers: on-off, proportional and PID. On/Off Control An on-off controller is the simplest form of temperature control device. The output from the device is either on or off, with no middle state. An on-off control device will switch the output only when the temperature exceeds the set point. For heating control, the output is on when the temperature is below the set point, and off above set point. Since the temperature crosses the set point to change the output state, the process temperature will be cycling continually, going from below set point to above, and back below.  In cases where this cycling occurs rapidly, and to prevent damage to switches or contactors, an on-off differential, or “hysteresis,” is added to the controller operations. This differential requires that the temperature exceed set point by a certain amount before the output will turn off or on again. On-off differential prevents the output from “chattering” or arcing. On-off control is usually used where a precise control is not necessary. Proportional Control Proportional temperature controls are designed to eliminate the cycling associated with on-off control. A proportional controller decreases the average power supplied to the heater as the temperature approaches set point. This has the effect of slowing down the heater so that it will not overshoot the set point, but will approach the set point and maintain a stable temperature. PID temperature Controller The third controller type provides proportional with integral and derivative control, or PID. This digital temperature controller combines proportional control with two additional adjustments, which helps the unit automatically compensate for changes in the system. These adjustments, integral and derivative, are expressed in time-based units; they are also referred to by their reciprocals, RESET and RATE, respectively. The proportional, integral and derivative terms must be individually adjusted or “tuned” to a particular system using trial and error. It provides the most accurate and stable control of the three controller types, and is best used in systems which have a relatively small mass, those which react quickly to changes in the energy added to the process. Categories

Renewable Energy What is renewable energy?  Renewable energy is generated from natural resources such as the sun, wind, and water, using technology which ensures that the energy stores are naturally replenished.   What are the benefits of installing renewables? There are lots of good reasons to use renewables. You will be: making use of secure and local resources reducing your dependence on non-renewable energy helping to reduce the production of carbon dioxide and other greenhouse gases creating new jobs in renewable energy industries reducing your energy bills. In some cases you can generate income by selling your surplus energy back to your energy provider.  Categories

Introduction to Heat Transfer Introduction to Heat Transfer Heat transfer is the exchange of thermal energy between physical systems. The rate of heat transfer is dependent on the temperatures of the systems and the properties of the intervening medium through which the heat is transferred. The three fundamental modes of heat transfer are conduction, convection and radiation. Fourier Law of Heat Conduction When there exists a temperature gradient within a body, heat energy will flow from the region of high temperature to the region of low temperature. This phenomenon is known as conduction heat transfer, and is described by Fourier’s Law (named after the French physicist Joseph Fourier), This equation determines the heat flux vector q for a given temperature profile T and thermal conductivity k. The minus sign ensures that heat flows down the temperature gradient. Heat Equation (Temperature Determination) The temperature profile within a body depends upon the rate of its internally-generated heat, its capacity to store some of this heat, and its rate of thermal conduction to its boundaries (where the heat is transfered to the surrounding environment). Mathematically this is stated by the Heat Equation, along with its boundary conditions, equations that prescribe either the temperature T on, or the heat flux q through, all of the body boundaries W, In the Heat Equation, the power generated per unit volume is expressed by qgen. The thermal diffusivity a is related to the thermal conductivity k, the specific heat c, and the density r by, For Steady State problems, the Heat Equation simplifies to, Derivation of the Heat Equation The heat equation follows from the conservation of energy for a small element within the body, heat conducted in        +      heat generated within  =      heat conducted out      +        change in energy stored within We can combine the heats conducted in and out into one “net heat conducted out” term to give, net heat conducted out=      heat generated within  –       change in energy stored within Mathematically, this equation is expressed as, The change in internal energy e is related to the body’s ability to store heat by raising its temperature, given by, One can substitute for q using Fourier’s Law of heat conduction from above to arrive at the Heat Equation, Temperature limits of some common insulation materials are indicated in the table below: Insulation Material Temperature Range Low High (oC) (oF) (oC) (oF) Calcium Silicate -18 0 650 1200 Cellular Glass -260 -450 480 900 Elastomeric foam -55 -70 120 250 Fiberglass -30 -20 540 1000 Mineral Wool, Ceramic fiber     1200 2200 Mineral Wool, Glass 0 32 250 480 Mineral Wool, Stone 0 32 760 1400 Phenolic foam     150 300 Polystyrene -50 -60 75 165 Polyurethane -210 -350 120 250   Calcium Silicate Insulation Non-asbestos Calcium Silicate insulation board and pipe insulation feature with light weight, low thermal conductivity, high temperature and chemical resistance. Calcium Silicate thermal conductivity Cellular Glass Insulation Cellular glass insulation is composed of crushed glass combined with a cellulating agent. These components are mixed, placed in a mold, and then heated to a temperature of approximately 950 oF. During the heating process, the crushed glass turns to a liquid. Decomposition of the cellulating agent will cause the mixture to expand and fill the mold. The mixture creates millions of connected, uniform, closed-cells and form at the end a rigid insulating material. Cellulose Insulation Cellulose is made from shredded recycled paper, such as newsprint or cardboard. It’s treated with chemicals to make it fire- and insect-resistant, and is applied as loose-fill or wet-sprayed through a machine. Fiberglass Insulation Fiberglass is the most common type of insulation. It’s made from molten glass spun into microfibers. Mineral Wool Insulation Mineral wool is made from molten glass, stone, ceramic fibre or slag that is spun into a fiber-like structure. Inorganic rock or slag are the main components (typically 98%) of stone wool. The remaining 2% organic content is generally a thermosetting resin binder (an adhesive) and a little oil. Polyurethane insulation Polyurethane is an organic polymer formed by reacting a polyol (an alcohol with more than two reactive hydroxyl groups per molecule) with a diisocyanate or a polymeric isocyanate in the presence of suitable catalysts and additives. Polyurethanes are flexible foams used in mattresses, chemical-resistant coatings, adhesives and sealants, insulation for buildings and technical applications like heat exchangers, cooling pipes and much more. Polystyrene Insulation Polystyrene is an excellent insulator. It is manufactured in two ways: Extrusion – which results in fine, closed cells, containing a mixture of air and refrigerant gas Molded or expanded – which produces coarse, closed cells containing air Extruded polystyrene, or XPS, is a closed-cell, thermal plastic material manufactured by a variety of extrusion processes. The main applications of extruded polystyrene insulation are in building insulation and construction in general. Molded or expanded polystyrene is commonly called beadboard and has a lower R-value than extruded polystyrene. Polyisocyanurate Insulation Polyisocyanurate or polyiso is a thermosetting type of plastic, closed-cell foam that contains a low-conductivity gas (usually hydrochlorofluorocarbons or HCFC) in its cells. Categories

Electrical standards and approved codes of practice Listed below are some commonly used electrical standards and approved codes of practice. Additional standards and codes of practice would generally be needed to satisfy a specific application – it is the responsibility of the specifier to select and apply these. You should ensure that the standard you use is the current one. The standards are organised into a number of topic areas and are ordered with the lowest number at the top of each table: Electrical and Power Electrical Appliances Electromagnetic Compatibility Flammable Atmospheres Machinery Electrical and Power Standard Year Description BS EN 61439 (many parts) 2009 – 2012 Low-voltage switchgear and control gear assemblies BS 5266 Parts 1 to 10 also BS EN 50172 1999 – 2008 Code of practice for emergency lighting BS 5424 Parts 2 and 3, also IEC 60158 part 3 1985 – 1988 Specification for low voltage control gear BS EN 60422 2008 Monitoring and maintenance guide for mineral insulating oils in electrical equipment BS 5839 Parts 1 – 11, also PD6531:2010 1988 – 2010 Fire detection & alarm systems for buildings BS EN 60079-30-2 2007 Electric surface heating BS 6423 1983 Code of practice for maintenance of electrical switchgear and control gear for voltages up to and including 1 kV BS 6626 2010 Code of practice for maintenance of electrical switchgear and control gear for voltages above l kV and up to and including 36 kV BS EN 62305, 4 parts 2006-2011 Code of practice for protection of structures against lightning BS 7375 2010 Code of practice for distribution of electricity on construction and building sites BS 7430 1998 Code of practice for Earthing BS 7671 2008 – 2011 Requirements for electrical installations. IEE Wiring Regulations. Seventeenth edition BS 7909 2008 – 2011 Code of practice for temporary electrical systems for entertainment and related purposes. BS EN 50110 Parts 1 and 2 2004 – 2010 Operation of electrical installations IEC 60479 Parts 1-4, also PD6519 1994-2005 Guide to effects of current on human beings and livestock. BS EN 60529 1992 Specification for degrees of protection provided by enclosures (IP code) BS EN 60947 Parts 1-8 2001 – 2011 Specification for low voltage switch gear and control gear   Electrical Appliances Standard Year Description BS 1362 1973 Specification for general purpose fuse links for domestic and similar purposes (primarily for use in plugs) BS 1363 Parts 1 -5 1995 – 2008 13 A plugs, socket-outlets and adaptors. BS EN (IEC) 60309, Parts 1,2, 4 1999 – 2007 Plugs, socket-outlets and couplers for industrial purposes. BS EN 60320, Parts 1, 2 1999 – 2009 Appliance couplers for household and similar general purposes. BS EN 60335, Many parts   Specification for safety of household and similar electrical appliances   Electromagnetic Compatibility Standard Year Description BS EN 61000-6-3,4 2007 – 2011 Electromagnetic compatibility. Generic emission standard. BS EN 61000-6-1,2 2005 – 2007 Electromagnetic compatibility. Generic immunity standard. BS EN (IEC) 60801, Part 2 1993 Electromagnetic compatibility for industrial-process measurement and control equipment. Electrostatic discharge requirements   Flammable Atmospheres Standard Year Description EEMUA 181 1995 Guide to risk based assessments of in-situ large Ex e & Ex n machines EEMUA 186 1997 A Practitioners handbook – electrical installation & maintenance in potentially explosive atmospheres BS EN 1127, Parts 1,2 2007 -2008 Explosive atmospheres. Explosion prevention and protection. Basic concepts and methodology for mining PD CLC/TR 50404: 2003 Code of practice for avoidance of hazards due to static electricity. BS EN 61241 2004, 2005 Electrical apparatus with protection by enclosure for use in the presence of combustible dusts. PD CLC/TR 50427 2004 Assessment of inadvertent ignition of flammable atmospheres by radio-frequency radiation. Guide BS EN ISO 10497 2004 Testing of valves. Specification for fire type-testing requirements BS 7535 1992 Guide to the use of electrical apparatus complying with BS 5501 or BS 6941 in the presence of combustible dusts BS EN 60079, many parts 2004 Electrical apparatus for potentially explosive atmospheres. Replaced by BS EN 60079, but remains current. BS EN 60079-6 2007 Explosive atmospheres. Equipment protected by oil immersion “o” BS EN 60079-2 2007 Explosive atmospheres. Equipment protected by pressurized enclosures “p” BS EN 60079-5 2007 Explosive atmospheres. Equipment protected by powder filling “q” BS EN 60079-1 2007 Explosive atmospheres. Equipment protected by flameproof enclosures ‘d’ BS EN 60079-7 2007 Explosive atmospheres. Equipment protected by increased safety ‘e’ BS EN 60079-11 2007 Explosive atmospheres. Equipment protected by intrinsic safety ‘i’ BS EN 60079-22-2 2007 Explosive atmospheres. Gas detection. Selection, installation, use and maintenance of detectors for flammable gases or oxygen Energy Institute Model Code Of Safe Practice, Part 1 (IP1) 2010 Electrical Safety Code Energy Institute Model Code Of Safe Practice, Part 15 (IP15) 2005 Area classification code for installations handling flammable fluids Energy Institute Model Code Of Safe Practice, Part 21 (IP21) 2002 Guidelines for the control of hazards arising from static electricity   Machinery Standard Year Description BS EN ISO 13850 2008 Safety of machinery. Emergency stop. Principles for design. BS EN 953 1997 – 2009 Safety of machinery. Guards. General requirements for the design and construction of fixed and movable guards BS EN 13849 2008 Safety of machinery. Safety related parts of control systems. General principles for design BS EN 982 1996  -2008 Safety of machinery. Safety requirements for fluid power systems and their components. Hydraulics BS EN 983 1996  -2008 Safety of machinery. Safety requirements for fluid power systems and their components. Pneumatics BS EN 1037 1996  -2008 Safety of machinery. Prevention of unexpected start-up BS EN  ISO 12100 2010 Safety of machinery. General principles for design. Risk assessment and risk reduction. BS EN 1088 2008 Safety of machinery. Interlocking devices associated with guards. Principles for design and selection. PD 5304 2005 Safe use of machinery BS EN 60204 many parts   Safety of machinery. Electrical equipment of machines. BS EN 61069, Parts 1-8 1991-1999 Industrial-process measurement and control. Evaluation of system properties for the purpose of system assessment. BS EN 61310, Parts 1,2,3 2008 Safety

Common Terms Specifications: BS 7671 – British Standard Also known as the IEE (Institute of Electrical Engineering) wiring regulations and is the standard that all electrical installations must adhere to. Circuit An assembly of electrical equipment supplied from the same origin and protected against over current by the same protective device(s). Circuit Breaker or RCD A device capable of making, carrying and breaking normal load currents and also making and automatically breaking, under pre-determined conditions, abnormal currents such as short-circuit currents. It is usually required to operate infrequently although some types are suitable for frequent operation. RCD – Residual Current Device Residual current device is a safety device that switches off the electricity automatically when it detects an earth fault, providing protection against electric shock.Distribution Board An assembly containing switching or protective devices (e.g. fuses, circuit-breakers, residual current operated devices) associated with one or more outgoing circuits fed from one or more incoming circuits, together with terminals for the neutral and protective circuit conductors. It may also include signalling and other control devices. Means of isolation may be included in the board or may be provided separately. Overcurrent Electrical current (in amps) that exceeds the maximum limit of a circuit. May result in risk of fire or shock from insulation damaged from heat generated by overcurrent condition. Part P The specific section of the Building Regulations that provides minimum safety standards for domestic electrical installations.  The Building Regulations are a devolved power so the actual requirements may vary across the UK dependent on which country the work is being done in. Portable Appliance Testing (PAT) Inspection and testing of electrical equipment including portable appliances, moveable equipment, hand held appliances, stationary equipment, fixed equipment/appliances, IT equipment and extension leads. Periodic Inspection Report (PIR) An electrical survey to reveal if electrical circuits are overloaded, find potential hazards in the installation, highlight any lack of earthing or bonding and carry out tests on the fixed wiring of the installation. The report is known as an Electrical Installation Condition Report (EICR) and will establish the overall condition of all the electrics, state whether it is satisfactory for continued use and detail any work that might need to be done. Prospective fault currentThe value of overcurrent at a given point in a circuit resulting from a fault between live conductors. Categories

CE Mark CE is an acronym for the French phrase “Conformite Europeene” and is similar to the UL or CSA marks of North America. Unlike UL or CSA which require independent laboratory testing, the CE mark can be applied by the manufacturer through a “self-certifying” procedure that verify that products are designed to the appropriate standards. The European Union has issued 24 directives related to the CE mark. Before manufacturers and exporters can CE-mark their products and legally sell them to, or within, the European common market, they must be in compliance with the applicable CE Marking Directive. The CE mark states that the manufacturer confirms the product to be within applicable EU directives. Note! The CE Marking is not a safety mark and must not be confused with a certificate. CE marking will never be granted by a third party test house or a certification body.1) The manufacturer is responsible for non-compliance and liable for any damage caused by the product. If the manufacturer (or his authorized representative) is not based within the EU, the importer is responsible for the product in Europe. If a product is not in compliance with the directives, it may be restricted, prohibited from sale or even withdrawn from the market. 1) Be aware that this is not always true. It depends entirely on which European Directive the CE-marked product has to comply with. For example the Pressure Equipment Directive # 97/23/CE requires a 3rd party (“notified body”) for some products that have specific pressure & dimensional characteristics (that are specified in the directive), so you are not allowed to apply the CE mark (i.e. you can’t sell your products & issue the CE certificate) if no notified body has approved your design/quality/manufacturing documents. Categories

ATEX ATEX is the name commonly given to the two European Directives for controlling explosive atmospheres: 1) Directive 99/92/EC (also known as ‘ATEX 137′ or the ‘ATEX Workplace Directive’) on minimum requirements for improving the health and safety protection of workers potentially at risk from explosive atmospheres. Specifications: An explosive atmosphere is defined as a mixture of dangerous substances with air, under atmospheric conditions, in the form of gases, vapours, mist or dust in which, after ignition has occurred, combustion spreads to the entire unburned mixture. Gases, vapours, mists and dusts can all form explosive atmospheres with air. Hazardous area classification is used to identify places where, because of the potential for an explosive atmosphere, special precautions over sources of ignition are needed to prevent fires and explosions. Categories