Safety


Unfortunately, that is not enough. Another signifi cant source of energy is static electricity. If a polymer case is used in the design of an intrinsically safe device, then the plastics themselves must be tested to be anti-static. This process involves conditioning - again - and then a surface conductivity test to confi rm that a charge cannot be created.


Even if all these challenges are successfully met, the unit must still pass what is called an ingress protection or IP test and a drop test.


The drop testing requirements for an intrinsically safe device are severe. In the case of the camera shown in Figure 2, the entire device is frozen to -10 degrees C for an extended period. Then the device is dropped multiple times onto concrete.


If the drop test does not result in noticeable damage, the IP testing is subsequently performed ON THE SAME TEST SAMPLE.


13


This is different from a standard ISO 9001:2000 quality management system and far more stringent with respect to inspection, testing and acceptance. For Nationally Recognised Testing Laboratories (NRTL) certifi ed devices, additional quality control is needed, as are additional audits. This is the case even if the manufacturer already manufactures ATEX equipment and vice versa.


As a manufacturer adds certifi cation marks to the device, the requirement for additional quality control and subsequent third-party audits also increases.


Typically, for devices certifi ed for use in the United States or Canada, these audit frequencies are once per quarter. For European ATEX certifi ed products, the audit is generally on an annual basis.


Conclusion


Whether the device uses intrinsic safe, explosion-proof, purge and pressurised, or any other protection concept, the aim is the same: To create a device or system that is safe to use in the environment for which it is intended.


Typically, hazardous area devices are more expensive than those intended for use in safe areas and it is easy to see why.


The challenges and risks associated with certifi cation mean that design cost and time are dramatically increased. Once a device is certifi ed, the cost to manufacture is also far higher than for a non-certifi ed unit. Special material and processes, increased quality control and multiple audit costs result in a higher cost to the end user.


However, this price is insignifi cant when compared with the time required to raise permits for non- certifi ed devices, not to mention the potential cost of fi nes and litigation should a non-certifi ed device cause harm by virtue of its use.


Figure 3 shows the fi nal result of the IP5X testing, after the drop test.


Quality Control


Now that we have established the design parameters, created a product and had it certifi ed, we can start selling it, right?


Unfortunately, not!


Quality control is a major challenge with the creation of any explosive area device. As a safety- related device, the control and repeatability of manufacture is paramount. In Europe, ATEX certifi ed equipment requires a separate Quality Assurance Notifi cation (QAN) for the device to be legally sold.


Figure 3: Pre and post IP5X testing About the Author


Tony Holliday currently serves as Director at a number of design and manufacturing establishments. Holliday began his careers as a Design Engineer creating intrinsically safe and explosionproof metering and control systems primarily for use in the Oil & Gas Industry and progressed into automated switchgear design and commissioning before taking a role as International Sales Manager for Cockburn Thermal Imaging Ltd. Subsequent roles include Sales & Marketing Director at Hawk IR International Ltd. and General Manager for Fluke Electronics IR Window business.


A published technical author and presenter, Tony brings a wealth of experience and knowledge across a broad base of industrial sectors.


All of our articles are online! To view and download them, visit: www.petro-online.com


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