Perhaps the LDH is Angus “Black Angus” hose? Angus were reputedly the first to introduce LDH in the UK, and the idea of having it colored black was a marketing pun. Bull? The Home Office had already issued six inch hoses to the AFS several years earlier, but I never saw any so I have no idea what color it was. Angus marketed their “ new “ big hoses in the US too, until local firms started to supply their own large diameter hoses - usually in five inch ( 125 mm ) diameter, but it was always natural light grey back then.
Now LDH comes in all kinds of colors, just like every other size fire hose, and some fire services color code their hoses according to diameter, although there does not seem to be any specific standard way of doing this.
I would have thought black is the last color you want to stretch along a roadway, especially at night...
Added by Rob Johnson on 10 August 2019.