PVC and Fire

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PVC in Building Construction, PVC Products and Fire

PVC and Fire

Toxicity levels of PVC end products in fire

Building & construction industry accounts for 35-37% of the total consumption of PVC. It is estimated that more than 4 million tons of PVC is used in this sector. PVC is considered as a prime polymeric material for building & construction industry on account of:

		PVC products are cost effective polymeric material & have a long life span from minimum of 5 years to as high as 50 years. This is one of the prime reasons for its use in the building & construction industry.
		Fire resistance is required to be assessed in several aspects. First is ignition of the product. Ignition temperature of PVC is 390 degree C compared to 240-250 degree C of wood. PVC is therefore more difficult to get ignited compared to the standard wood that is very widely used in the building industry. Fire resistance of PVC product depends upon the amount of plasticizer. Higher level of plasticizer reduces resistance to fire. PVC corrugated sheet being mainly rigid, contains no plasticizer. Hence PVC corrugated sheet has high resistance to fire. PVC products including pipe, window profile, wire/cable & corrugated sheet are excellent in their resistance to fire.
		Another aspect that requires to be measured is the amount of oxygen in the environment that will initiate fire in a product. PVC containing more than 55% chlorine has excellent property. It requires 40% of oxygen when the atmospheric oxygen content is merely 21% at ambient temperature. At its ignition temperature, PVC requires 21% of oxygen. In other words, PVC will catch fire only at 250 degree C under normal atmospheric condition.
		When product catches fire it releases heat. PVC product generates 20000 KJ/ Kg, while the most widely used polyolefin product would release 46000 KJ/KG & gasoline would release 44000 KJ/KG. PVC is therefore superior in this aspect also.
		Once a product catches fire it could smoke. While polyolefin does not emit smoke, PVC is deficient in this aspect. PVC emits smoke. Specific optical density of gases arising from burning of PVC is 400 while wood typically has optical density of 550-600 depending upon type of wood. Special additives like zinc borate, aluminum hydroxide etc could reduce smoke density notably. PVC wire product is designed with such additives to control smoke density.
		During smoke generation, some toxic gases could also emerge. PVC on burning generally produces hydrochloric acid in the form of gas. This acid being corrosive could damage the plant equipment. It would also cause rusting of wall of an incinerator. This could reduce waste disposal of PVC after fire. Incinerator could be designed on stainless steel so that acidic hydrochloric acid would not corrode the wall of incinerator. However, this design would increase capital cost but on a long term when capital is amortized it contributes a very little amount higher than that for normal material of construction of incinerator.
		During smoke generation, toxic gases would also be emitted. PVC on burning typically generates hydrochloric acid, carbon monoxide & carbon dioxide. Water is also generated along with these 3 gases. Carbon dioxide is considered as low toxic material. L/D 50 value for carbon monoxide is 1300. Carbon monoxide & hydrochloride both are considered toxic Their L/D 50 values are 27 & 22 respectively. It is advisable to stay away from PVC fire, but if not possible then face should be covered by mask and should be accompanied by a respiratory system.
		In burning of PVC, along with the major portion of the above 3 gases, small amount of dioxin & furan. These are toxic. However their generation is actually very small. In fact, burning of wood generates more dioxin & furan compared to burning of PVC. The laboratory analysis conducted by Swedish authority found that only 1/1000 th amount was of both dioxin & furan was measured on a gram of PVC. L/D 50 value of dioxin is 0.025.
		In short, PVC is considered to be safe for use in building & construction industry. It can be safely said & concluded that PVC is not harmful & is comparable to timber product. Only precaution is required that face should be covered with mask to prevent from suffocation, nausea & fainting.
		PVC corrugated sheet is not compared to timber but is compared to asbestos or glass or fiberglass reinforced product since PVC corrugated sheet is an alternative to these 3 materials. Asbestos could cause cancer. It is therefore seen that asbestos corrugated sheet is phased out except in the developing & economically weaker regions.
		Glass is brittle compared to PVC corrugated sheet. Unbreakable glass would be equally expensive or even higher. PVC would be favoured on price. Fiberglass reinforced sheet also would be more expensive.

Disposal of PVC product in fire

		PVC products having majority of its applications with long service life generally has limited presence in municipal waste beyond which PVC can not be recycled without deterioration or any conventional waste. Packaging that has service life of less than 1 year is only a small application of PVC. Only about 10-15% of PVC is used in packaging. Besides, its usage is gradually reducing. It is therefore only surprising that only less than 0.2 % of PVC is found in waste.
		PVC product including corrugated sheet used in building & construction appear in waste only after minimum of 5 years. Typically the service life is at least 25 years. However its disposal needs to be understood.
		PVC can be disposed ideally by recycling. Significant quantity of PVC can be recycled since PVC product comes in different mechanical properties from very soft (like footwear) & flexible to very rigid such as corrugated sheet. Typically rigid PVC product is recycled in less demanding applications of flexible plasticized. However, there is a limit beyond which PVC cannot be recycled without deterioration of mechanical properties & therefore of performance.
		Second waste disposal system that can be used for PVC is that of land filling. However, over the last 50 years & gradual use of this method for waste disposal has now reduced the spare place that can be land filed. It will not be possible to consider this option as one of the waste disposal for PVC very soon.
		Third waste disposal system that can best be adopted for PVC is that of incineration in which PVC is put in furnace & heat or energy is generated. All polymers are rich in energy content since they are all derived from oil & can be considered as solidified oil with some chemical modification. For instance PVC because of only 43% of organic content generates less heat or energy compared to polyolefin. The only problem with incineration of PVC is that it would emit hydrochloric acid, which in turn will make the incineration plant from inside corroded. Higher capital cost would be required in order to design incinerator with material that will not corrode. However on a long term the amortization would increase the cost only marginally. Incineration is therefore the most suitable method of disposal for PVC.
		PVC in fire would generate hydrochloric acid, carbon dioxide, carbon monoxide in greater proportion. Dioxin & furan will be generated in very small quantities (less than 0.05%). All of these being gaseous in nature at higher temperatures that will exist in fire will get lost to the atmosphere. Only very minute quantity of ash will be generated arising from additive such as heat stabilizer, lubricant & fillers etc. This ash can easily be removed after the fire gets extinguished. In other words the disposal of PVC in fire does not require any special treatment.

Life of PVC product

		Life of PVC product depends upon compound formulations. Typically rigid PVC products such as pipe, window & other profiles & corrugated sheet.
		PVC corrugated sheet being rigid contains very small quantity of low molecular weight additives. These additives are responsible for reduction of life time of PVC product. Due to presence of very small amount of additives, PVC corrugated sheet has longer life.
		Corrugated sheet being exposed to ultra violet light is liable to degrade & deteriorate unless it is stabilized with special light stabilizer. Generally corrugated compound formulation always contains light stabilizer to the extent so that it could provide longer life. Typically corrugated sheet is designed to provide at least 10 years life. Most of the suppliers design their compound formulation to provide life of 15 years.
		When fire takes place all PVC products cease to survive & therefore end their life prematurely. Only metal products can survive & can be used again after cleaning etc. PVC as well as all plastic can not survive & end their life.