The Health and Safety Executive (HSE) has warned contractors that allowing workers to sleep on construction sites increases the risk of work injuries.
Contractor Asaad Al-Helu was prosecuted after allowing five migrant Polish workers to use a site in Hull as sleeping accommodation on premises which contained a large amount of flammable material.
Employees were put at risk as there was no means of escape or raising the alarm in the event of a fire, which could have led to heavy injury compensation claims for Mr Al-Helu.
It is also understood that the contractor had not prepared a construction plan before work began on the site in addition to a lack of safe working practices in being put in place.
"One carelessly discarded cigarette could have had serious and possibly fatal consequences, not only for them but also for local residents," warned HSE inspector John Rowe.
Landlords have also recently been advised of the danger fire risks pose to their tenants, following the prosecution of one property holder from Cambridgeshire who was fined £14,000 for failing to obtain a gas safety certificate.