感謝前警員爆料，向眾志披露警隊內部戰術文件，唔知幾時檔案會被刪，歡迎各位有心人盡快BACKUP： tiny.cc/HKPtactics
// 從文件内容得知，警員發射催淚彈前，要考慮「風速及漩流可能受到地勢之影響」，「街道兩旁圍着高層之建築物會引致漏斗效應」，影響催淚煙擴散走向。可見昨日警方在元朗靠近民居及老人院區域施放催淚煙，實險像橫生，犯上戰術錯誤。
文件上有圖解戰術例證，指示「在場之高級人員須確保當向人群使用催淚煙時，需留有逃走之路線。此點非常重要。群眾如無逃走之機會則不應向其使用催淚煙—因群眾會產生恐懼而盲目地向人襲擊。」//
Generally, the funnel effect describes the phenomenon where winds will tend to increase in speed as they squeeze through narrow valleys and it can be explained by Bernoulli’s theorem. According to this, the pressure is least where velocity is greatest and in the same way pressure is greatest where velocity is least. The same phenomenon can be observed in urban areas and especially in city center where the built density is higher than in rural areas (Fig_06). So, referred to urban areas, the funnel effect, or double corner effect is where two adjacent surfaces squeeze the air between them, resulting in an increase in wind speed (Reiter, 2010; Abohela, 2012). The wind can accelerate between linear urban arrangements and create an unpleasant and a lot of times dangerous environment for the pedestrians. When designing an urban space, knowledge of wind pressures, speed, velocity is often required to allow the prediction of “well-use”. Even in existing spaces and environments the data in these conditions are useful in order to locate problematic areas. This kind of data can be generated either through wind tunnel measurements or computational fluid dynamics (CFD) predictions. The wind data can be found out by these techniques even in the scale of pedestrian level evaluating the flow of wind and analyzing the outdoor comfort criteria. (Wu et al., 2012).
Fig_06
