Fireproofing, also known as passive fire protection, refers to the process of increasing the fire resistance of structures or materials. The term fireproofing does not necessarily mean that the fire won't affect the fireproofed item or the fireproofed item cannot ever burn. When an item is fireproofed, it means that the item gets protection from the fire to a certain time or duration based on the measured performance of the fireproofing material under certain tests and evaluation.
Fireproofing is divided into two disciplines, that are active fire protection and passive fire protection. Passive fire protection is used in oil refineries or industrial process plants to minimize the escalation of fire that could result from structural failure and overheating of pressure vessels. Damage that the fire could do too soon can add significant fuel to the fire.
The traditional fireproofing method used earlier was to pour the concrete or gunite in place around the item to be fireproofed. Such fireproofing systems are too heavy and make life difficult to install at higher elevations or areas where heavyweight are not allowed (e.g. offshore). the fireproofing industry has come up with a solution by discovering the fireproofing system based on vermiculite and epoxy instead of concrete.
The vermiculite-based fireproofing systems are lighter in weight and are installed at all elevations, however, they are not so strong as the concrete-based fireproofing, and are prohibited to use at lower elevations or areas prone to mechanical abuse. There is a trend of using concrete-based fireproofing from the ground to 1 meter followed by vermiculite-based fireproofing to the rest parts of the structures.
The purpose of Fireproofing
Basically, fireproofing is used to protect the structural steel that carries risky or valuable equipment. The breakpoint of steel is commonly referred to as 535˚C, as this is the point at which the steel loses approximately half (i.e. 50%) of its strength. So the goal is to keep the steel from reaching 535˚C for a certain period of time. The time we buy or want the fireproofing to maintain the integrity of the steel in the event of a fire is between 15minutes to 240 minutes. The time period that a fireproofing gets after certain testing in an independent laboratory is known as the time rating or fire resistance period (FRP).
Over time, the fireproofing may degrade or get damaged from the element's in daily plant life so it is at most important to protect and maintain the fireproofing so that in the event of a fire, the fire resistance properties remain constant in order to fulfill the intended functions.
Daily exposure in the plant includes but is not limited to the following;
Contact with oils, solvents, chemicals, etc.
The term fireproofing may mislead many people because no material is completely fireproofed. All materials used in the construction are susceptible to fire. What we mean when we say fireproofing is the fire-resistance, which means, we try to withstand potential fire situations over a period of time. The goal of fireproofing is to minimize the overall damage caused by the fire. The fireproofing enables us to take action, while we are in the fire resistance period. The fire resistance period gives us time to extinguish the fire, turn off the fuel supply to the fire and try all possible ways to evacuate the personnel and to stop the process (fire).
The decision to make the industrial process plant fireproof is made on the basis of risk analysis. First, consider the type of fire and then evaluate the required fire life for a variety of equipment including structural steel, pressure vessels, exchangers, pipes, and the like. The location of certain equipment in a process plant is just as important as the location of the plant in relation to neighboring facilities.
The fire resistance period and test methods
No single fire test method is representative of an actual fire situation and therefore there is no best or accurate test method available. Standardized tests simply provide a basis for relative comparisons of fire-resistant materials and structures.
When fire protection is required, the degree of fire resistance depends on the application in the process plant. Typical requirements for the protection of an oil refinery or process plant may be as follows;
For structural steel, installation may require a 2 to 3 hours fire resistance period (FRP). A thickness between 50mm to 75mm may be appropriate to achieve the said FRP. Lightweight cementitious (vermiculite based), or Epoxy-based intumescent are common materials for use, however, the traditional fireproofing material based on concrete may also be an option.
Equipment may require 1 to 2 hours FRP with 40mm to 50mm fireproofing thickness. The fireproofing materials that provide the equivalent fire resistance period may be used to protect the equipment from fire.
Plates and frame heat exchangers are of particular interest because of the rubber gasket material used between the plates. These heat exchangers are equipped with a protective cover designed to prevent the maximum operating temperature of the heat exchanger from exceeding approximately 1 hour. The maximum operating temperature is the temperature specified by the equipment manufacturer (or vendor) and is common at <150˚C.
Passive fire protection generally falls into the following three categories:
Lightweight cementitious based on exfoliated vermiculite
Intumescent based on epoxy or acrylic
The potential of concrete as a fireproofing material has long been recognized. Many refineries built before World War II used dense concrete extensively as fire protection. This material is inexpensive and is known to withstand extreme temperatures. However, problems quickly arose: the concrete was heavy, resulting in excessive demands on the steel structures; This also means high labor costs, since forming concrete around the steel is a laborious, and multi-step process.
It has also been found that rapid cooling after a fire causes the concrete to crack and in some cases severely compromises the structural integrity of the material. This damage is sometimes difficult to detect and can be hazardous to those working on site. Dense concrete as fire protection has been largely abandoned in favor of new methods that provide superior performance and less inconvenience.
The lightweight cementitious fireproofing retains the advantages of being based on inexpensive raw materials (vermiculite) and not having the problem of being overweight. As the name suggests, the material is considerably lighter than concrete and therefore does not require excessive design specification However, lightweight fireproofing retains the high labor costs.
The major disadvantage with lightweight cementitious fireproofing is it tends to crack if inappropriately applied, and may create an inevitable space between the fireproofing and the substrate it was applied to. This space tends to collect moisture, which in turn causes corrosion under the fireproofing.
Intumesce means swell, so the fireproofing tends to expand in its thickness to several times in the presence of extreme heat generated by the fire, thus, an increase in volume and a decrease in density slow down the heating of the substrate, which increase the time before the steel loses its load-bearing strength or melts. The expansion, which is also known as the char, basically creates a larger barrier between the fire and steel.
The epoxy intumescent fireproofing tends to create the char up to 5 times the actual fireproofing thickness, and the acrylic-based intumescent fireproofing swells up to 50 times to its original thickness. The thickness of the char and the time that the fireproofing char remain in its place decides the fire resistance period.
The advantage of the intumescent fireproofing is that the fireproofing is lighter in weight among all and may fight corrosion in much the same way as traditional protective coatings.
While there are several standards available to use for the fireproofing work, some of the common standards that you may find helpful are listed here;
API RP 2218
API RP 2001
DNV GS D301