Intrinsic safety mitigates the explosive potential of hazardous areas
This is a two-part article on intrinsic safety. Read part two here.
Customers may request engineers to build safe machines. Engineers assume safety because most of us do not intentionally set out to not be safe. However, there are intrinsic safety design standards that are used in industry to try and guarantee safe environments and safe machines. Use of these guidelines can prevent incidents.
Intrinsic safety is a design technique that incorporates limiting the amount of energy available for ignition in a hazardous area. The kind of applications calling for intrinsic safety are boilers, power houses, fuel stations, fuel cell testing, chemical transaction areas, mines, kilns, fluid beds or any applications that could be susceptible to ignition due to gases, fumes, dust or fibers.
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For instance, certain metals may be flammable, and, if you pile shavings from making airplane parts and then provide an ignition source, a fire could be started that is not put out by water. Temperature plays a huge role in the processing of certain flammable materials, and so does water. Note that oxygen is included in air. What are the three things needed to make a fire? Fuel, heat and oxygen.
Fire engineering studies the fire triangle, and results are used to warn firefighters on how to treat certain types of fires. This knowledge also applies to making a machine safe—how do engineers deter a fire or combat and isolate a fire if it does occur?
Materials and technology changes beg that engineers and machine designers stay abreast of changes. Some fires are not extinguishable with water. Other materials must burn themselves out. Dismissing the pillars of intrinsic safety could be devastating.
Engineers comply by building machines with low-energy signaling—24 V— in hazardous areas. Intrinsic safety is designed to protect low-energy systems or signals.
Create safety barriers that limit the times of transmissions and reduce heat, dust or any kind of combination that could cause an explosion. Purchase cards and equipment that meet International Electrotechnical Commission Explosive (IECEx) certification, the European Union's Atmosphères Explosibles (ATEX) directive and explosion-proof environment standards. In short, these are governing bodies that provide legal and regulatory frameworks to create electronics usable in a potentially explosive environment.
ATEX certification shows a machine to be compliant with European Union directives for proving safety in specific environments and explosive atmospheres. Products complying with these standards will be labeled.
Machine builders wanting to meet European standards will be required to certify their builds, much like Underwriters Laboratories (UL) builders do.
Occupational Safety and Health Administration (OSHA) has similar standards for installing machines in hazardous areas, which require specific wiring methods, classified locations and air flow. These standards reference the National Electric Code (NEC) and National Fire Protection Agency (NFPA).
There are physical requirements and electrical requirements, as well as wiring measures that reduce sparks or threat of ignition. For instance, electrical boxes need to prevent dust entry in a hazardous environment. OSHA also has marking standards that include the area classification, symbols, type of protection designations, gas classification group, if required, and temperature classification.
Class I, II and III are noted by NFPA 70 and then divided into two divisions and then up to four groups. These classifications are based on gases or vapors, combustible dust and ignitable fibers.
How do we fight the potential for combustion in these categories? Engineers set up boundaries, use air flow and reduce flammability reactions based on wiring, conduits and ductwork.
Software-wise, alarms are set up to protect an area and to shut down faulted equipment and turn on air flow to evacuate the area of combustibles. If the machine is in an area that houses many of these machines, then the machines are daisy-chained so that, if one machine faults, they all shut down due to the flammability in the area.
This adheres to machine zoning and the control of the process. Zoning hazardous areas is critical due to having controlled entry and controlled actions such as no smoking, no cell phones and no naked lights. Automation engineers can deploy safety gating and regulate zones with badges or keys or operator-control-room interface and request-to-enter gates.
Part II of this article covers PLCs and HMIs in hazardous areas.
