Re: Bonding Rail cars for unloading Flammables
friebel -
I want to be real clear that I am not downgrading any of the safety aspects your are talking about. I believe you are correct in thinking static electric discharges can be dangereous.
However, some of the concepts you stated do not match up with my research or experience.
Originally posted by friebel:
... Let me give you an example of a job that I had of grounding of rail cars to eliminate Static Electricity when unloading or loading. This was in a hazardous area, classified as 1-2-D.
I purchased a unit from the Crouse-Hinds Company that made sure that you had a good ground connection to eliminate a build-up of static electricity. ...
I'll bet a cup of yuppie coffee the CH unit did not check the ground connection. Rather it checked the bonding wires were attached to a low impedance (metallic) path. - two ways I've seen this done:
1. The bonding cable has two conductors, connected to the jaws of a bonding clamp. The unit checks to see if there is a low resistance between the two clamp jaws. This type works well when clamped to a piece of galvanized steel and thrown in the dirt. Administrative controls are required to ensure the ground/bond clamp is used properly.
2. The bonding cable is terminated in a proprietary plug. A matching receptacle is required on the tanker. This type still only checks that there is continuity between two of the pins - again not checking any grounding.
The units depend on the installation to provide a good ground to the clamp and administrative controls to use it instead of cheat it.
Originally posted by friebel:
... grounding rail cars for unloading or loading to eliminate static electricity. You would want a reading to ground as low as possible. ...
According to the API spec, bonding is important for protection against ignitions, but grounding does not reduce the risk. The API spec does point out there are other considerations that determine the required grounding.
Originally posted by friebel:
Static Electricity is a very dangerous situation, especially in a hazardous area, and you need to have personnel knowledgeable to know how to eliminate a Static build-up.
Okay, this one is touchy. I don't want to say it is not dangerous. Like most everything else, if one does not know what he are doing ...
APR RP 2003, para 4.2.5.6
In most cases, static-related fires within tank truck compartments have involved either the loading of an intermediate vapor pressure product or switch loading (see Section 4.1.4.2). Recently, it has been estimated that the frequency of static related tank truck loading ignitions is about one per one million loadings and have involved at least one of the two previously mentioned conditions. In most of these ignitions, the cause of the incident was attributed to the failure to follow recognized procedures and guidelines. However, in the few incidents where all safety procedures appear to have been followed, many of the risk factors were present at levels close to established safety limits.
I absolutely agree that one needs to be knowledgeable to mitigate the risks.
carl