Is 'Defensive Engineering' Next?

With an out of control regulatory environment in Washington, we expect doctors to practice defensive medicine. Is defensive engineering next? What happens when OSHA regulators disagree with state fire marshals? We now have an example of Obama-engineering to consider.

One company in Illinois has been told by an OSHA inspector to install an emergency pressure relieving device on a water tank to handle the admittedly rare but ominous "fire case." The Illinois State Fire Marshal told the same company not to bother. So who should prevail in this case of dueling regulators? You decide.

The state relies upon the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. That code differentiates between fired pressure vessels, such as boilers and water heaters, and unfired pressure vessels. It requires pressure relieving devices such as relief valves or rupture discs in cases where there exist scenarios where there is a reasonable chance that a pressure excursion will occur due to some defined source. The ASME was founded in 1880 by engineers in response to a rash of fatal boiler explosions. Water in a closed pressure vessel that is subjected to a heat source can eventually heat up to the boiling point and begin to vaporize into steam. As the amount of steam increases, so does the pressure. Too much pressure can lead to an explosion due to the vessel walls failing under the stress. These scenarios are known as "cases" and are evaluated for the purposes of sizing any relief devices.

A "fire case" is one where there is an external source of heat due to a fire surrounding the vessel. Normally, fire cases are developed only for vessels containing flammable liquids. Fires can radiate huge amounts of energy onto the walls of the vessel, thereby heating its contents. If, for example, a pipe used to fill the tank with gasoline developed a leak and the resultant pool of gasoline was ignited, one can easily see why it makes sense to have an emergency relief vent to prevent the tank from exploding and spreading flaming gas everywhere around it.

But why would one do the same for a simple tank containing only water? The fire marshal, having practical experience in fighting real fires, is unconcerned. He understands such basics as the "fire triangle", where to have a fire you need three things, fuel, oxygen and a source of ignition. You can't have a fire without fuel. Without a fire to provide the heat source, the threat of a water storage tank explosion is negligible. The wet-behind-the-ears OSHA safety inspector has federal government regulations to use to threaten plant managers with fines to get his way.

As a plant manager, would you buckle under the threats and install a "Potemkin village" emergency vent to get the OSHA inspector to go away? Would you practice defensive engineering? Or would you embarrass the Federal Government by exposing the idiocy of its safety inspectors? Fortunately, for the plant manager, he asked someone on the outside with a public platform on the American Thinker for advice. As a service to plant managers everywhere, let me offer a solution.

The first thing to do is to document the "fire case" by describing the location of this hypothetical scenario. It is inside a masonry building with ceramic tile floors. The primary contents of the room are gleaming sanitary stainless steel tanks and their associated piping. What combustible material exists, maybe the paint on the walls, a few pieces of paper, insulation on the electrical wires, and a few plastic fixtures, is quite limited. But the theoretical chance of a fire does exist. To meet this "threat", we will install a rupture disc in a screw holder with six outlet holes. If the pressure in the tank exceeds the set pressure, the disc will burst allowing steam to escape as if through the caps of six tea kettles. This will produce a warning sound to alert the occupants to the problem. The steam will then begin to permeate throughout the room displacing the air and starving the fire of oxygen. We will have created an emergency water based fire extinguisher to put out the fire.

Do you think OSHA will buy the concept?

Bruce Thompson


With an out of control regulatory environment in Washington, we expect doctors to practice defensive medicine. Is defensive engineering next? What happens when OSHA regulators disagree with state fire marshals? We now have an example of Obama-engineering to consider.

One company in Illinois has been told by an OSHA inspector to install an emergency pressure relieving device on a water tank to handle the admittedly rare but ominous "fire case." The Illinois State Fire Marshal told the same company not to bother. So who should prevail in this case of dueling regulators? You decide.

The state relies upon the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. That code differentiates between fired pressure vessels, such as boilers and water heaters, and unfired pressure vessels. It requires pressure relieving devices such as relief valves or rupture discs in cases where there exist scenarios where there is a reasonable chance that a pressure excursion will occur due to some defined source. The ASME was founded in 1880 by engineers in response to a rash of fatal boiler explosions. Water in a closed pressure vessel that is subjected to a heat source can eventually heat up to the boiling point and begin to vaporize into steam. As the amount of steam increases, so does the pressure. Too much pressure can lead to an explosion due to the vessel walls failing under the stress. These scenarios are known as "cases" and are evaluated for the purposes of sizing any relief devices.

A "fire case" is one where there is an external source of heat due to a fire surrounding the vessel. Normally, fire cases are developed only for vessels containing flammable liquids. Fires can radiate huge amounts of energy onto the walls of the vessel, thereby heating its contents. If, for example, a pipe used to fill the tank with gasoline developed a leak and the resultant pool of gasoline was ignited, one can easily see why it makes sense to have an emergency relief vent to prevent the tank from exploding and spreading flaming gas everywhere around it.

But why would one do the same for a simple tank containing only water? The fire marshal, having practical experience in fighting real fires, is unconcerned. He understands such basics as the "fire triangle", where to have a fire you need three things, fuel, oxygen and a source of ignition. You can't have a fire without fuel. Without a fire to provide the heat source, the threat of a water storage tank explosion is negligible. The wet-behind-the-ears OSHA safety inspector has federal government regulations to use to threaten plant managers with fines to get his way.

As a plant manager, would you buckle under the threats and install a "Potemkin village" emergency vent to get the OSHA inspector to go away? Would you practice defensive engineering? Or would you embarrass the Federal Government by exposing the idiocy of its safety inspectors? Fortunately, for the plant manager, he asked someone on the outside with a public platform on the American Thinker for advice. As a service to plant managers everywhere, let me offer a solution.

The first thing to do is to document the "fire case" by describing the location of this hypothetical scenario. It is inside a masonry building with ceramic tile floors. The primary contents of the room are gleaming sanitary stainless steel tanks and their associated piping. What combustible material exists, maybe the paint on the walls, a few pieces of paper, insulation on the electrical wires, and a few plastic fixtures, is quite limited. But the theoretical chance of a fire does exist. To meet this "threat", we will install a rupture disc in a screw holder with six outlet holes. If the pressure in the tank exceeds the set pressure, the disc will burst allowing steam to escape as if through the caps of six tea kettles. This will produce a warning sound to alert the occupants to the problem. The steam will then begin to permeate throughout the room displacing the air and starving the fire of oxygen. We will have created an emergency water based fire extinguisher to put out the fire.

Do you think OSHA will buy the concept?

Bruce Thompson


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