CARTAGENA, Colombia, April 24 (Reuters) - BHP Billiton is flying workers into its ferronickel plant in Colombia with a hired helicopter to resume production as laborers block access to the site in a stoppage the company says is illegal, an official said on Friday.
Unionized workers have been blocking access to the Cerro Matoso ferronickel mine and processing plant for about 10 days in protest over a change to 12-hour shifts from eight previously.
BHP Billiton says the measure will boost efficiency amid comparatively low nickel prices while workers say it heightens risks to their health. London-traded three month nickel rose to $13,196 per tonne on Friday.
Ferronickel production was halted altogether at one point during the stoppage, but the company has resumed a small amount of processing again since it began flying workers into the premises for two-day stints during which they sleep on site.
"We have adapted the facilities so they can spend the night. We have been able to start production again which is very good news," Vice-President for External Affairs, Luis Marulanda told Reuters at the Colombian Mining Association conference.
Though production volumes are only a fraction of usual output, a resumption of processing will help avert damage to the plant's furnaces, worth tens of millions of dollars, by cutting the amount of time they tick over on lower power.
The purpose of the reduction to two daily 12-hour shifts instead of three shorter eight-hour shifts is to boost productivity by reducing working time lost during hand-over processes, Marulanda said.
"In this scenario of lower prices, you need to produce at a lower cost," he said.
Marulanda said the company remains open to dialogue with the workers who represent about half the total employees. Union leader Domingo Hernandez said the longer shifts will raise health risks from lengthier exposure to harmful substances.
The company says the stoppage is illegal because the union does not have enough members to meet the 50 percent plus one of total workers required to declare a strike. Hernandez, however, says unionized workers make up a little over half the total. (Reporting by Peter Murphy; Editing by Grant McCool)