Smoke floats were pretty dodgy cargo. Made in light gauge metal they had a habit of splitting open and depositing corrosive chemicals on the deck and /or sailors. As a result they were never stowed below decks and always close to the stern where they could be jettisoned double quick. They could be ignited on the deck but only if stood on a steel plate usually they were lit and thrown overboard. They usually floated for about an hour. On deck they may have been chocked on the deck but I suspect they were never heavily lashed down and disposed of with the prospect of heavy weather.