A scrapyard wall that collapsed on five men, crushing them to death, "could have gone at any time", an inquest has heard.
Health and Safety Executive expert Martyn Ostcliffe said the 11.8ft (3.6m) wall collapsed in Birmingham in 2016 due to an "overloaded bay of scrap".
The inquest previously heard hundreds of tonnes of metal spilled on top of the men at Hawkeswood Metal Recycling.
Mr Ostcliffe told the inquest: "This wall was overloaded and not safe."
Ousmane Diaby, 39, Bangally Dukureh, 55, Saibo Sillah, 42, Muhamadou Jagana, 49, Alimamo Jammeh, 45, died at the plant on Aston Church Road in Nechells.
The men had been clearing out a scrap metal storage bay at the time, when the wall of an adjacent bay fell on them.
Birmingham Coroner's Court heard evidence from Mr Ostcliffe, a civil engineer, who had visited the scene on 15 July, days after the incident.
Coroner Emma Brown asked how he established the wall collapsed.
He replied: "I'm experienced enough to know ... from the density of one brickette that the wall collapsed because it was overloaded."
Mr Ostcliffe told the inquest he carried out various calculations on the forces pushing and resisting against the wall to establish "factors of safety" used in engineering.
Any factor of less than one is a failure, he said.
Only needed a trigger
Mr Ostcliffe said: "This wall was overloaded and not safe. All factors of safety came in as less than one.
"In my view it could have gone at any time. It only wanted a trigger to give it that last - just something that would just sent it over."
A height of 1.7m would have been a safe height for the brickettes against the wall but on the day it was 3m, he said.
Mr Ostcliffe made a number of suggestions about what caused the wall to fall including the removal of material from the bay the men were working in, the use of machinery in the bay or the brickettes expanding due to temperature.
He said there were no risk assessments in place and he would have expected routine inspections of structures roughly every week or more.
When asked by Frank MacGuinness, who is representing the families, about the safety inspections carried out by Hawkeswood senior staff, he agreed they were "a tick-box exercise".
"It wasn't a reliable system to me," Mr Ostcliffe added.
The inquest continues.