Anton Burrows, 24, was helping a telescopic forklift truck driver lift the beam on to two brick pillars at a Huddersfield housing construction site on April 7 last year.
As the forklift withdrew, it dislodged the beam which fell on Mr Burrows as he walked into that particular area of Strata Homes Yorkshire Ltd's Suede Development.
Mr Burrows, from Bradford, sustained severe spinal injury and is now quadriplegic.
The Health and Safety Executive (HSE) prosecuted Strata Homes Yorkshire, of Quay Point, Lakeside, Doncaster for its role in the accidents at work.
The company pleaded guilty to breaching Regulation 8 of the Lifting Operations and Lifting Equipment Regulations 1998 and was fined £30,000 and ordered to pay £16,062 in costs.
After the hearing, HSE Inspector Alasdair Green said: "Had the lifting operation been properly planned and supervised, in line with the regulations, the Approved Code of Practice and HSE's guidance, this devastating incident which could have very easily killed someone, would have been avoided."