An Evaluation of Smoke Toxicity and Toxic Hazard of Electrical Nonmetallic Tubing Combustion Products

Abstract

Small-scale smoke toxicity tests were performed on polyvinylchloride-based electrical nonmetallic tubing (PVC/ENT) using the National Bureau of Standards (NBS) protocol for nonflaming combustion. An LC 50 of 28.5 mg/L ( & p l u s m n ; 9.25) was determined, placing PVC/ENT smoke in a toxicity category comparable to smoke from wood.Four large-scale tests were conducted in a 21,734-L room (8 x 12 × 8 ft). In tests involving 18 to 30 linear in. of PVC/ENT with and without fuelcontributing heat sources, it was learned that: a) 30 in. of PVC/ENT developed a 3.3-mg/L smoke concentration and an insufficient HCl concentration to cause death or significant symptoms in test animals (rats) and b) in the presence of a relatively small fire (5-lb wood crib), heat and carbon monoxide became lifelimiting prior to HCl. In additional tests involving approximately 60 in. of PVC/ENT degraded under 2.5 Watts/cm 2 heat flux, a smoke concentration of 7.6 mg/L was developed. Animal fatalities in these tests were shown to be from heat stress rather than smoke inhalation. The measurable percents of theoretical yield of HCl in small-scale tests ranged from 64 to 96 percent and in large-scale tests from 23 to 50 percent. The reasons for these differences are discussed.

Hydrogen Chloride Transport and Decay in a Large Apparatus: II. Variables Affecting Hydrogen Chloride Decay

“…There are many similarities between the experimental set-up used by Packham and Crawford for the work referred to in the previous paragraph [22] and some of the experiments carried out for the present work. It is, therefore, important to calculate the experimental yields of HCI obtained, as well as some of the implications, of their work.…”

“…One paper of particular interest is an attempt [22] to scale up one of the small-scale combustion toxicity tests, viz. the University of Pittsburgh test [26,27]: PVC-based electrical non-metallic tubing (PVC/ ENT), surrounding THHN-insulated wire (which also contains PVC), was decomposed in a 21,734 L (8 ft x 12 ft x 8 ft) room.…”

Use of an Approximate Lethal Exposure Method for Examining the Acute Inhalation Toxicity of Combustion Products

“…Since the flaming experiments did not exhibit this variability, it is most likely due to slight differences in the combustion conditions of the test material. The production of toxic gases during sample combustion has been previously shown to be dependent on temperature [4,12,20], presence of flame [2,12], and oxygen availability at the site of combustion [21,22]. However, since those conditions were unlikely to vary substantially under the prespecified heating conditions, it is possible that sample heterogenity may have been a factor.…”

Hydrogen Chloride Transport and Decay in a Large Apparatus I. Decomposition of Poly(Vinyl Chloride) Wire Insulation in a Plenum by Current Overload

“…Hydrogen chloride was monitored by two different procedures: (a) soda lime tubes (SLT) [8,20,22] and (b) syringes (SYR) [6,19]. In the SLT method, a stream of chamber atmosphere was drawn through a 1/8 in.…”

“…Although numerous examples exist of small-scale toxicity tests [4] and of small-scale experiments, it has generally been found difficult to correlate the results with those of large-scale fires [19,20]. It is therefore important to carry out such experiments in a scale which is large enough to be representative of a real fire.…”