Food Protection Trends - May/June 2024 - 154

FIGURE 1. Floor plan of fruit and vegetable processing plant. Red X shows the placement of the superheated steam source.
Green circles show the placement of RH and temperature data loggers. In total, there were eight probes that were placed at 0.3
and 1.5 m away from four locations, including the superheated steam nozzle, vents, walls, and entrances, respectively. Black
squares show the vent locations in the facility. The blue shade represents areas within the enclosed space of a facility.
Ambient RH and temperature measurement
Baseline RH levels and temperatures were measured by
using data loggers (EL-WiFi-TH, EasyLog, Erie, PA) over 30
min. The data loggers were equilibrated for 1 h prior to the
start of experimentation. A schematic floor plan of the fruit
and vegetable processing plant and the placement of the eight
data loggers recording RH and ambient temperature within
the space are shown in Fig. 1. The superheated steam source
was positioned in the approximate center of the space (red
X), and the data loggers (green circles) were placed 0.3 m (1
ft) and 1.5 m (5 ft) away from the superheated steam nozzle,
entrances, and vents. All loggers were placed at the same
height that the superheated steam nozzle was positioned
above the floor. Distances (0.3 and 1.5 m) between the
superheated steam nozzle outlet and surfaces were selected
in accordance with the operating guidelines for the superheated
steam unit for sanitation efficacy. The RH at each
location was recorded continuously, and the temperature was
recorded every 15 min for up to 5 h. The superheated steam
equipment remained stationary at the same position throughout
the 5-h treatment time.
Superheated steam system and setup
The temperature of the superheated steam unit (HGA-S,
MHI Inc., Cincinnati, OH) was set to 135 ± 1°C, a typical
temperature for superheated steam application. The
superheated steam outlet temperature was equilibrated for
15 min and measured to be 135 ± 1°C between replications.
Approximately 1 liter of water was used over 5 h. Coupons
(30.5 by 30.5 cm and 0.15 cm thick) composed of stainless
154 Food Protection Trends May/June
steel (grade 304 2B; Rose Metal Products, Springfield,
MO) were placed vertically with the flat side facing the
superheated steam outlet and at a distance 0.3 m from
the superheated steam outlet to detect any condensation
formation (Fig. 2). Images showing surface condensation
on stainless steel coupons were captured every 5 min for up
to 15 min to qualitatively assess saturated steam formation
during the superheated steam application.
Ventilation rate assessment using a CO2
(6). The CO2
decay method
ACH was calculated for each space as previously described
level of the air outside of the test space was first
measured for 5 min near the air intake of the ventilation system
outside the building before each experiment. Then, CO2
decay
levels were determined inside the test spaces. To raise the
peak CO2
well mixed in the room. The CO2
levels inside the facility spaces to at least 2,000 ppm,
approximately 250 g of dry ice was placed in a cardboard box
and left in the room for 2 min. A small oscillating fan was used
to keep the CO2
level was
then measured at 1-min intervals by using a CO2
using the CO2 concentration decays (1, 22)
ACHDI = 1 Δt ln [(C1
handheld gas
detector (range 0 to 9,999 ppm, accuracy ± 50 ppm; GasLab
Plus, Ormond Beach, FL) for up to 2 h. The ventilation rate
was determined by CO2
clearance with dry ice (ACHDI) by
-CR) / (C0
-CR)](1)
where Δt is the period between measurements, C0
and C1
are
CO2 levels measured at the beginning and the end of the decay
period (ppm), and CR
is the CO2 level in outdoor air (ppm).

Food Protection Trends - May/June 2024

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