No abstract

No abstract

No abstract

No abstract

No abstract

Corn is an example of an agricultural grain with a specific combustibility level and can promote smoldering fires during storage. This paper conducts an experimental design to numerically evaluate how three parameters, namely particle size, moisture, and air ventilation, influence the smoldering velocity. The work methodology is based on Minitab’s experimental design, which defined the number of experiments. First, a pile of corn is heated by a hot plate and a set of thermocouples registers all temperature variations. Then, a full-factorial experiment is implemented in Minitab to analyze the smoldering, which provides a mathematical equation to represent the smoldering velocity. The results indicate that particle size is the most influential factor in the reaction, with 35% and 45% variation between the dried and wet samples. Moreover, comparing the influence of moisture between corn flour and corn powder samples, a variation of 19% and 31% is observed; additionally, analyzing the ventilation as the only variant, we noticed variations of 15% and 17% for dried and wet corn flour, and 27% and 10% for dried and wet corn powder. Future studies may use the experimental design of this work to standardize the evaluation methodology and more effectively evaluate the relevant influencing factors.

This article describes the development and demonstration of a non-intrusive method for the quantitative determination of speed of air movement along the ground and inside an isolated subsurface structure, a type of confined space. Natural ventilation occurs continuously and reduces risk to entrants from contact with a hazardous atmosphere. One of the most important parameters still undetermined was the speed of air movement during the process. Small puffs of artificial “smoke” were used to visualize air movement. Tracker, an open-source physics program, provided the capability to analyze this movement. Measurement of air speed requires access to individual frames in the video, capability to move forward and backward, and the means to manipulate the image to highlight the “smoke”. Background subtraction, control of brightness and contrast, and conversion of color to greyscale were essential for obtaining these measurements. Measurements for a single opening indicated that flow along the ground was borderline turbulent (Reynolds number ~3000) and in the opening and inside the airspace, within the bounds of laminar flow (Reynolds number <2250). Video obtained during this work showed behavior observable in laboratory studies of Helmholtz resonators. Results provide the basis for a larger study of the ventilation process to facilitate design improvements.

This article describes development and confirmatory testing of a method to study the evaporation of a volatile solvent containing ignitable ingredients in an isolated subsurface structure, a type of confined space. Accidental spillage and surreptitious disposal of chemical products in streets create a risk of fire and explosions in these structures. Development of the method included consideration about instrument safety; personal exposure; volume of the structure (2.5 m3); evaporation rate; temperature of the airspace; and number of opening(s) in the manhole cover. Confirmatory testing utilized 10 mL of lacquer thinner (60% to 80% toluene, 10% to 20% methylethyl ketone (MEK), 5% to 10% methanol and 1% to 9% acetone) on a wetted paper towel positioned near the bottom of the structure. This methodology produced a maximum of 2150 ppm of ‘isobutylene units’ on a PID (PhotoIonization sensor) positioned about 15 cm above the sample. This concentration corresponds to about 1140 ppm of toluene (less than 10% of the Lower Flammable Limit of 12,700 ppm). This method offers a stable, safe platform for study of the process. Evaporation of solvent and exchange between the external atmosphere and the airspace regulate the concentration of vapor, which can typically persist for 24 to 48 h.