Hazardous Atmosphere

A hazardous atmosphere is one where a substance is mixed with oxygen to produce the potential for explosions.  A wide range of substances can cause this condition.  Some such substances are volatile liquids such as petrol or gasoline, or explosive gases such as methane, hydrogen or propane.  The risk is not confined to volatile fluids. Combustible solids such as grain flour, coal dust or wood dust can also be lifted into the atmosphere to create dangerous conditions.

A number of international standards exist, including ATEX in Europe and IECEx internationally.  These standards identify hazardous environments as Zones or Classes and Divisions, based on the level of risk. Under ATEX, Zone 0, Zone 1 and Zone 2 are used to classify areas containing gases, mists or vapours.  Zone 20, Zone 21 and Zone 22 are used to describe areas containing combustible dust.

Equipment manufacturers design products that are intrinsically safe.  These products are sometimes described as explosion proof, but this is not entirely accurate.  Intrinsically safe equipment is designed so that their normal operation is unlikely to cause an explosion when used in a hazardous environment, normally by preventing them creating an effective ignition source.  The equipment manufacturers use a number of techniques to prevent the creation of an effective ignition source, including shielding, insulation and isolation.  In addition, the manufacturers may use different materials specifically to reduce or remove the chance of creating an effective ignition source.

Components that may be ATEX or IECEx rated include connectors, plugs and sockets; switches; boxes, cases, enclosures and cabinets; cable glands; luminaires and light fittings; sounders and beacons;   In addition, equipment that also might be certified could include: cameras and imaging equipment; grounding clamps; sensors.  Manufacturers who supply ATEX rated products include CEAG, Cordex, HARTING, Lapp, Newson Gale, Pepperl + Fuchs, PR Electronics, Rittal, Turck, Vega.

These effective ignition sources can include naked flames, sparks caused during the electrical or mechanical operation of the equipment, high surface operating temperatures or electrostatic discharge.

Manufacturers will usually specify the suitable zone in which their equipment may be safely used.  They may also mark the equipment with suitable labels for clear identification.

The ATEX rating is a European directive.  In the UK, the standards are applied under DSEAR (The Dangerous Substances and Explosive Atmospheres Regulations of 2002).  The equivalent in the US is the HAZLOC standard.  Internationally, the IEC (International Electrotechnical Commission) use the IECEx system.

Industries that may generate or be subject to hazardous atmospheres include the oil exploration, oil extraction and refining industries; gas extraction and distribution industries; mining; food handling; power generation; the manufacturing sector; and the research industry.

 

Harsh Environment

Equipment is often required to function in less than ideal conditions.  Equipment might be exposed to extremes of temperature, vibration, shock, water or chemicals.  Equipment manufacturers will provide information to explain how their devices can be used.

Many engineers use the IP rating to describe a device’s protection against water ingress. IP stands for Ingress Protection.  The rating is written as (for example) IP65.  The two digit number describes the protection of the device.  It is sometimes followed by a suffix.  For example, a rating of IP64 describes protection against splashing water, IP68 protects against immersion in water beyond 1 metre in depth (often up to 3 metres), and IP69K describes protection against high-pressure jets of water (as in spray-down or cleaning situations).

The suitability for operation in extreme temperatures will be noted by an operating temperature.  This will usually consist of a minimum and maximum temperature, and will usually show the temperature range within which a device may be expected to perform indefinitely.  Sometimes an extra temperature will be stated, usually a maximum temperature and an associated time period. This is a temperature that a device can resist for a short period of time, before the temperature needs to be reduced to within the standard operating temperature.  This is important for a component that is soldered, which will be subject to higher temperatures for the time it takes to solder.  It is also important to remember that high temperatures combined with other conditions may require additional protection.  For example, salt water / seawater that is heated to a higher temperature can have adverse effects on certain materials (e.g. unprotected aluminium).

IP ratings are often applied to: connectors, backshells, plugs and sockets; switches, keypads; fans and HVAC equipment; boxes, cases, enclosures and cabinets; cable glands, conduit and trunking; luminaires and light fittings; sensors and transducers.

Manufacturers who supply IP rated products include, Amphenol, APEM, Bulgin, Carlingswitch, Cherry, Deutsch, Fibox, Fischer, Hellermann Tyton, Lapp, Lemo, Lumberg, Molex, Otto, Panasonic, Pepperl + Fuchs, Souriau, Switchcraft, TE Connectivity

Equipment that is attached to moving or powered machinery may be subjected to vibration or shock.  Vibration is measured in hertz (cycles per second), or with reference to cycles per minute.  Acceleration is measures in metres per second per second (m/s2) or with reference to the gravity at the surface of the earth noted as G where 1G = 9.81 m/s2.  The amplitude of the vibration (the distance that is displaced away from the rest position) might also be measured.  Shock is usually measured as a force, often again in units of gravity (G)

 

Materials

A thorough understanding of the conditions likely to be encountered will be vital to help make choices regarding materials, but even then this choice will be a compromise between several competing requirements.

As an example, aluminium is a lightweight, electrically conductive metal that has applications across many industries, but it is very vulnerable to salt water corrosion.  As an alternative, plastics are less vulnerable to corrosion and are also lightweight, but they are not electrically conductive and can be vulnerable to UV radiation damage.  If very high tensile strength is required, both aluminium and plastic would be poor choices compared to stainless steel, but this would have a considerable impact on weight.

It is also interesting to note that materials are vulnerable in environments that might appear safe at first glance.  The domestic kitchen, for example, presents a number of hazards to product designers.  The presence of highly acidic fluids (orange juice), aggressive chemicals (cleaning materials) and high temperatures can all play havoc with materials.

Materials that might be considered for harsh environments include aluminium; nickel aluminium bronze alloy; stainless steel, titanium; PEEK; PBT; Liquid Crystal Polymer; ceramics and porcelain; phosphor bronze; composite materials; rubber and silicon rubber.