Nitrogen Not So Safe
Re: your October 2010 Editor's Page ("Change the Game," www.ControlDesign.com/change), you are aware that nitrogen is not a "safe" gas. Fatalities occur every year because of nitrogen exposure. I don't know the process used to machine titanium, but a single oxygen sensor (possibly with its own internal alarm) would not provide a safe environment safeguard in an indoor application. I think a dual or triple redundant sensor system with external TMR safety system would be more appropriate to meet OSHA requirements. An emergency exhaust system might be called for to be automatically tripped by voting on several sensors.
A hazard and operability analysis (HAZOP) and safety integrity level (SIL) analysis on the process are in order. A company I worked for had a fatality because a man simply stepped too close to an open flange on a vessel containing nitrogen in an outdoor environment. There is no warning smell or feeling. Many times the rescue people are killed trying to save the first one down.
Has the vendor thought of using compressed or liquid air as the cooling medium? If the small quantities of gases other than oxygen would be a refrigeration problem, perhaps a special mixture of 80% nitrogen and 20% oxygen could be used as the refrigerant. This would take the entire hazard away if the refrigerant is checked for composition as it is received and used.
Joseph "Dal" Dalferes, PE,
Principal Control Systems Engineer,
Jacobs Engineering, www.jacobs.com
Listen to Those Voices
I hope more manufacturers of machines will listen to the voice of the customer and view your Embedded Intelligence column ("Listen for the Change," www.ControlDesign.com/listen) as an opportunity.
We can no longer afford to have one-off brands or even spares of brands. We need consistency and backward compatibility of existing items. And what everyone would like (and some provide, thankfully) is to have legacy compatibility with something manufactured last year or five or more years ago, without purchasing a whole new left-handed XYZ. People do not like the crossed-finger moments waiting on a rep who knows someone who knows someone who might have something from an OEM surplus event or cannibalized from someplace with unknown lineage.
Len Walsh, Engineering Fellow,
Pratt & Whitney, www.pw.utc.com
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