FOCUS
FIREX International 2018
was faster at the centre and decreasing going outwards. With increased pressures, a similar pattern emerged – droplets were consistent and of a similar shape. The total data collection found that droplets with a larger surface area would have a greater heat transfer, but this was difficult to accurately calculate. Issues included that not all droplets were of the same size, while size was also inconsistent across the spray pattern (but larger on average at the edge). The tests allowed the laboratory to calculate
the total surface area and volume of the droplets, and estimate surface area for any given volume of water on a proportionate scale. Overall results found that pressure and surface area increased concordantly, with a strong positive correlation.
Crowd behaviour Watermist systems
The FPA’s John Harbottle and George Edwardes explored research, development and testing of watermist systems, Mr Harbottle noting this project focused on pressure affecting spray pattern and droplet size. Testing aimed to find out how much water is dispersed by each nozzle, with 25 tested across different pressures. Mr Edwardes spoke about the spray angle
test, which used a solenoid valve to activate and turn off water. The framework was kept still and the tank pressurised, a mounted camera on a tripod taking images processed to calculate angles, which tended downward as pressure increased. Also tested was the K-factor, or relationship
between water discharge and pressure, and results showed it remained consistent across most pressures. In terms of droplet size and velocity, smaller droplets were found to have a larger surface area to volume ratio and thus more momentum, achieving better penetration and reaching the seat of the fire. Mr Edwardes added that droplet size was also studied using a laser analysis system and a high speed camera. Around 10,000 droplets were captured
in 60 seconds, figures taken from the centre of the test to 40° allowing for estimations of droplet diameter, volume and surface area. At 0°, droplets were 50 microns; 100 microns at 20°; and 250 microns at 40°, despite having a smaller surface area. Consecutive images spotted duplicates and established each droplet’s velocity, with the slowest found at the centre and fastest at 40°. A separate test studied spray cone distribution, with a custom built table featuring 100ml concentric rings collecting water, which
34 JULY/AUGUST 2018
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University of Brighton’s Dr Chris Cocking stated that the ‘irrational’ view of crowds as barbaric mobs influences response planning, viewing them as an ‘actual or potential threat’. It ignores social context, creating mistrust and assuming fear causes emotion to override reason, collective identity breaking down in a ‘contagion spread’. Withholding information – treating crowds as a problem not a resource – can delay evacuation. This has only been unpicked in the last 30
years, evidence finding the ‘total opposite’. Mass panic in emergencies is rare – in the 7/7, 9/11 and Grenfell events it was ‘noticeable by its absence’. Less than 1% of people escaping the World Trade Centre panicked, while Dr Cocking was on the Underground on 7/7, and he noted individual fear or distress, but also general calm, quiet and cooperation. Social bonds are created, people feel
they are ‘all in it together’, and ‘orderly, altruistic behaviour’ emerges, overruling selfishness, while lack of cooperation is often down to ability or physical constraints. Evidence showed antisocial behaviour was rare and ‘almost never spreads’, while wave management studies show tragedies are misinterpreted as mass panic or stampedes, detailed post analysis finding the opposite. Panic is often used to ‘deflect’ from ‘potentially neglectful management’, painting ‘victims as villains’. Pushing is ‘often unintentional’ due to pressure waves and dangerous density, also causing unintentional trampling. False alarms make it easy to criticise those unaware of details, and real warnings may be ignored in future. Like Grenfell’s community spirit and social justice campaign, Dr Cocking believes there is ‘a degree’ of shared identity post experience, warning that politics of resilience lead to assumptions that people will be fine, which can be used to cut infrastructure or guidance.
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