Running group Seletar Hash House Harriers yesterday apologised for the alarm and inconvenience it caused when three of its members used flour to mark a running route through Woodleigh MRT station.
Their actions set off a security scare and the station was closed for three hours on Tuesday.
The group, in a statement, said three of its members were marking a trail for its Tuesday evening run from Bidadari to Woodleigh Close.
The trio, who chose a route that ran through the station, left a little flour at three to four points in the MRT station to mark out the trail, as "this provided the safest route to cross Upper Serangoon Road".
One of its members, a 69-year-old man, was later arrested for causing public alarm. He is believed to be out on bail. The other two members, aged 53 and 70, are helping the police with investigations.
The station was closed after SBS Transit staff found a suspicious white substance and alerted the police. The Singapore Civil Defence Force's hazardous materials team was also deployed.
"In retrospect, they should not have placed any markings in the station, and instead, should have used directional signs outside the station," the statement said.
It added that the three members "stepped forward immediately to identify themselves and have cooperated fully with the authorities", after learning of the security scare.
"They are sorry that their actions caused public alarm and inconvenience," it said, noting that the incident emphasised the seriousness of the security threat in Singapore.
The group was set up in 1980 and now has around 100 members.
The members of the running group were following guidelines used around the world in marking a hash run, which is a mix of cross-country running and a treasure hunt. Flour or chalk is used to mark trails as they are organic, non-polluting substances that can be washed away easily, the statement said. In nature reserves and parks, only paper can be used but it must be cleared within 24 hours.
There are currently about nine registered hash running groups in Singapore, which is said to be home to the second-oldest hash movement in the world after Malaysia.
Runs are held almost every day of the week and members gather for food and drinks after the run.
Mr Ken Ong, who heads Hash House Harriers Singapore, said hash running started as "an underground sort of activity and attracted mainly colonial Englishmen through word of mouth".
Since then, it has expanded to include women-only and children's groups, as well as one involving dogs and their owners.
Mr Ong, whose group was founded in 1962 and is the oldest in the country, said hash running groups here will have to rethink using flour markings after Tuesday's incident. They may even decide to avoid places like MRT stations, major roads, shopping malls and pedestrian walkways during their runs.
Mr Charles Corrigan, a Singapore Sunday Hash House Harriers committee member, said while his group usually runs in forested areas, they are sometimes forced to run along roads or in public places. "Sometimes, there is just not enough forest left, and we will have to run on the street to connect up," he said.
His group, which organises runs that take place every fortnight on Sunday evenings, sees about 25 to 40 runners each time. They range from those in their 20s to those in their 60s. He said: "We have run past MRT stations before, without much trouble. It was unfortunate that this happened."