Plants With Hazards to Spare

Plants With Hazards to Spare

Cat crackers for refining oil are shown along with unprotected steel pipe and supports. Oil heater is at lower left.Pipe maze, with distillation towers in background is typical in petroleum plant. Note horizontal LPG storage vessels.

The oil refinery and the chemical plant are two of the occupancies that represent every facet of a fire fighter’s nightmare. In these occupancies are such traps as unprotected steel supports, chlorine and hydrogen in both high-temperature ignition sources and high-pressure/high-temperature processing units.

All of these plants, by the nature of their business, must handle materials in bulk, which means that most have unprotected truck and/or rail loading racks, pipeline terminals usually supported by unprotected steel, or large high-hazard warehouses for solid materials and liquids up to drum-size containers. At the same time, undiked and poorly drained aboveground tanks are usually present in abundance to complicate exposure protection.

And the workhorses of the industry are not limited to solids and liquids. The gases have their place and must be handled differently, even though a large percentage of them are actually processed in the liquid state.

Plant components

Most chemical plants and refineries must contain the following fundamental components: (1) fractional distillation towers, (2) stripping and scrubbing units, (3) reactors, (4) pipe racks and trenches (with associated valves, fittings, etc.), (5) loading racks and (6) refrigeration machinery. It is the intent of this article to deal with these components and their relation to the petrochemical industry because they are problem areas common to most plants no matter what their location.

A fractional distillation unit usually comes in the form of a tower 25 to more than 200 feet high. It is used to separate materials having different boiling points. Crude oil, for example, is a mixture of many hydrocarbons and can be separated by distilling. At lower temperatures, the lighter portions (methane, ethane, propane, etc.) vaporize, and these lighter ends are collected off the top of the tower. At higher temperatures, the heavier portions can be pulled off.

The tower is usually steel, with its base raised off the ground to facilitate piping. Supports are usually constructed of reinforced concrete, but unprotected steel supports are still to be found. Of particular interest to fire fighters is the question, “Which way is the distillation tower going to fall in a fire?” Most of these towers are selfsupporting, rather than guyed. An exposure fire of any duration will take a heavy toll on unprotected steel because the rate of heat release of many hydrocarbon fuels is often many times that of wood.

A 100-foot tower filled with flammable gases and buckling under impinging flame would be a catastrophe, particularly if it buckled at the base and tore out pressure piping as it fell. Piping damaged by the fall would be quite another problem. The tremendous Btu release in a fire of this nature makes master stream devices not simply desirable, but absolutely necessary. Personnel cannot operate in the elevated temperatures that characterize distillation unit fires. Chief officers are fortunate if they get portable deluge sets close enough to a fire of this type for the stream to be effective.

Reactors and shortstops

Reactors may create quite a different problem when exposed to heat. Reactors are often pressure vessels constructed substantially enough to control temperature and pressure without undue loss to the atmosphere. Feed of products to the reactor is usually by piping, although inhibitors (shortstops) may be added by gravity, or top dispensing, from drums and barrels.

Horizontal vessels hold propane, butane and propylene.

Various products known as shortstops may be added to a reaction when its vigor begins to exceed the satisfaction of the process engineer and the design limits of the system. The shortstop will inhibit the speed of the reaction. In the plastic and rubber industries the primary reaction is polymerization, a chain reaction forming large complex molecules with a subsequent release of large amounts of energy, particularly heat.

The normal hazards, such as metal fatigue and corrosion, are present in reactor units, but the primary concern is control of the speed of the reaction. Such control may be maintained by refrigeration (such as ammonia systems); isolation of a reactor from a chain of reactors by closing valves (with the addition of a shortstop); stopping the flow of feedstock; or as a last resort, blowdown. Most production managers would rather do anything short of blowdown. The name of the game is still money, and blowdown is a complete loss of valuable products in most cases.

Two types of processes

Chemical processes usually run one of two ways, continuous or batching. In a continuous process, there is no convenient time to shut down the process for preventive maintenance, but in batching there is time available between batches. In the continuous process, it is necessary (1) to duplicate all components of the system, a very costly operation; or (2) to shut down the entire system for preventive maintenance and testing, also very costly; or (3) to run the process until it collapses at some failure point, often with disastrous results.

It is important in reactor areas to provide for a second line of defense. In addition to sprinklers and other automatic systems, monitors should be provided 50 feet but not more than 100 feet from reactors. Sprinklers serve their purpose, but an explosion is apt to take the sprinklers out of service. It also becomes important at this point to emphasize isolation valves on sprinkler systems to keep an open sprinkler riser from robbing precious water from monitor nozzles.

Single point failure analysis is also important in a chemical plant. The question is, “What can the plant do without?” In many continuous processes, the answer is “nothing.” Equipment such as electrical transformers, process compressors, boilers, etc., cannot be lost. Unless spares are provided on the line, there are no alternatives. Business interruption losses resulting from loss of these items is simply an unacceptable risk. They must be completely protected and maintained.

Pipe racks and trenches

Most inspectors and pre-fire planners are appalled by the vast quantities of pipe that process engineers can hang on process units. In spite of their need to be efficient and to properly support the process, pipes, racks and trenches seem to warrant little attention in some plants until, after 30 or so years of service, they malfunction. Most pipe in the chemical industry is subjected 24 hours a day to heat, cold, pressure, vacuum and vibration.

Pipe rusts, erodes and becomes brittle, leading ultimately to leaks and blowouts. Valves and fittings are subjected to these same conditions. Valves become difficult to manipulate. Fittings leak, often in the rack or trench where the leak is most difficult to detect, isolate and repair.

One problem that receives even less attention is elbow washout. In the course of pumping product through a pipe, the elbows where piping turns comers are subjected to greater than normal erosion. Tees are also susceptible to this same wear. Flange bolts tend to stretch under heat and stress. Gaskets become brittle and blow out.

Danger during fire

When subjected to the intense heat produced by fire in a refinery or chemical plant, pipe stretches and blows out, the flange bolts stretch from internal pressure, valves freeze in whatever position they are in and usually, with nothing to support it but unprotected steel supports, the whole fiery mess either falls to the ground or explodes in a photographer’s dream.

Dangers such as these can be avoided by use of low and high-pressure alarms in piping, periodic testing or inspection, product-detection systems that activate deluge or special extinguishing systems in milliseconds, and low and high-temperature alarms.

Pipe trenches, where vapors can accumulate and travel throughout the trench system, should, if not protected by automatic leak-detection systems, be monitored by personnel with flammable vapor detectors at least every four hours or once per shift. Any positive reading should be thoroughly investigated and the source eliminated immediately. Waiting for the next shift may be fatal.

Protection for pipes

Pipe racks should have a minimum of two-hour fire protection, with at least spray protection for the piping in the racks. Piping exposed to corrosive atmospheres should be painted or otherwise suitably protected to prevent deterioration of wall thickness.

Plant or emergency personnel should be able to isolate piping by closing valves or at least stop the flow of product through affected piping. Valves should be clearly marked. A comprehensive color code system is highly recommended so that each product may be readily identified.

Fire fighters should be alert for any coding system in their pre-fire planning. In this area, it is increasingly important for plant personnel to cooperate with and participate in training sessions for municipal fire companies responding on the first alarm and for municipal personnel to take full advantage of the information provided in their training sessions. Overhead piping is exceptionally difficult to deal with in emergencies.

It should also be noted at this point that in case of a high-pressure leak of any kind, but particularly gas or steam, noise levels will be such that verbal communication, including radio transmission, will be virtually impossible. A predetermined set of hand signals is an absolute necessity in such situations.

Separation by scrubbing

Stripping and scrubbing are, much like fractional distillations, the separation of products. Scrubbing usually consists of the addition of a compound to a solution to scrub out one or two elements of a compound by dissolving them.

This is better explained by example. Butadiene, used extensively in the rubber and plastics industries, is inhibited for transportation. The inhibitor imparts stability to an otherwise delicate substance. The inhibitor must be removed from the butadiene before introduction to a process because the inhibitor will keep it from reacting or polymerizing. This removal is done by bubbling the inhibited butadiene through a caustic solution. The inhibitor is dissolved in the caustic, and the uninhibited butadiene is pulled off the top.

In a scrubbing process such as this, not only does the fire fighter have to deal with a highly flammable and reactive substance, but with a highly corrosive one as well. Corrosiveness also increases maintenance. The scrubbing unit must be continually maintained in the above example because caustic will cause rust and decay in the system.

Stripping explained

Stripping is the removal of a product from a liquid by evaporation, distillation or the passage of a gas through the liquid. This process utilizes a difference in volatility to separate products.

A good example of this is the introduction of steam into a column to strip unpolymerized or unreacted styrene from rubber latex. The steam serves to heat the styrene and the styrene floats to the top of the column where it is pulled off to be recycled through the process. The problems that can arise in stripping are as unlimited as the products that can be used.

Primarily, fire fighters must realize that products with very different properties may be involved. In the example above, for example, rubber latex is a water solution, while styrene polymerizes violently with a tremendous heat release.

Refrigeration

Refrigeration in a petrochemical installation not only controls the environment within buildings, but also is instrumental in the control of reactions. The loss of the refrigeration may make the difference between the reaction going critical and remaining under control. The refrigeration system often uses a gas as a heat transfer medium. The heat contained in a vessel being cooled changes the refrigerant from a liquid to a gas and then the compressor changes the gas back to a liquid.

Industry uses a number of gases for this job, depending on what is the most efficient for the money. Some processes have a gas for a byproduct. If this gas is a good refrigerant, it will be used. The point is that seldom is any consideration given to flammability or toxicity. It is a common practice to use flammable gases as refrigerants. Gases that are used include methane, ethane, propane, ethylene and propylene.

Fire fighters should be alert for these gases in fire situations and should attempt to uncover their use in pre-fire planning. The release of these gases in a fire situation is sure to increase personnel fatalities.

Fire fighters also should be alert for diffusion systems around refrigeration systems. These consist of a tank filled with water or other solvent to which the refrigerant may be released in an emergency. In ammonia systems, this tank contains water which readily absorbs ammonia. After absorption, the water may be released to a waste collection system. These systems save personnel from exposure to toxic situations if they are properly used.

Action by fire fighters

Some diffusion systems may require that fire fighters pump water into the systems for mixture with the refrigerant. This will depend on individual systems and should be investigated during pre-fire planning. In case of unexpected release of refrigerants, selfcontained breathing apparatus will be an absolute necessity. If these units are not provided in adequate supply by public agencies, the plant should be required to supply them.

Another coolant process that deserves mention is the use of high flash point liquids such as kerosene to cool high heat processes. Most systems of this type consist of a tank, a closed piping system and a pump. In some cases, these liquids may be used to cool a high heat process and heat a low heat process, making use of waste heat.

As was stated before, the name of the game is money. Granted, these liquids have high flash points, some as high as 250 degrees, but in a pressure system containing no air, the liquid temperature may be on the order of 600 degrees. Any leak in a pipe, pump packing, etc., will likely be ignited on release. If not ignited, the fire fighter will have a tremendous vapor cloud to contend with which is capable of releasing thousands of Btu in milliseconds.

Loading racks are of particular concern in a chemical plant because this is possibly the only place in the plant where all the materials used in the process will be together at the same point in time. Knowledge of the reactions possible between materials is a must in the loading rack area.

Spill control in this area is likely to be critical. It is important that drip pans be provided to catch product left in fill hoses when loading and unloading is completed. Provisions must also be made for proper disposal of drip pan contents.

Aside from the normal loading rack provisions for static grounding, explosion-proof electrical wiring, portable extinguishers and good personnel discipline, remote control valves should be provided as well as automatic extinguishing systems that protect both the rack and the vehicle.

A second line of defense is also necessary at multi-product, racks. Monitors should be provided in sufficient quantity to adequately protect the area. These monitors should be predirected to properly cover the area and should be activated by detection devices.

Drainage is another situation that is apt to be critical in the loading area. The best automatic systems cannot be expected to control a flammable liquid fire if the flammable liquid is not contained in a well-defined area. Loading racks should be constructed below grade or curbed or properly drained to a sump pit. Drains should be provided with flashback traps to prevent propagation of the fire to sump systems. Any variations from the above precautions should be taken into consideration and, if possible, corrected.

Pre-fire planning needed

All the processes and mechanical difficulties mentioned will continue to maim or kill operators and fire fighters until we in the fire and safety field take an aggressive position on pre-fire planning and correction of faults. The items mentioned are only as safe as people make them. The “hands off attitude” by authorities and the willingness to stay away have not altered the situation and never will.

Just as there are people out to make a fast buck, there are corporations out to do the same. But in this industry, the price of that buck is apt to be a human life. How much is one worth? Explosions caused by these problems are not particular about whom they kill.

The fire fighters who survive these incidents are the ones who have the knowledge to cope with the situation.

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