How Pretius digitized on-site safety with an offline-first mobile app

The client is one of the largest and best-known construction companies in its market, running building contracts across the whole country. A general contractor of that size doesn't manage a workforce so much as a constantly shifting population: thousands of its own employees plus the employees of its subcontractors, arriving at and leaving dozens of sites, each of which has its own safety requirements, permits, and daily rhythm.

Safety supervision at this scale is a genuinely hard logistics problem before it is a software problem. Every worker on a site needs to be the right worker, with valid qualifications and up-to-date safety training, and every day begins with briefings that have to actually reach the people doing the work. Done on paper, as it had been, this generates exactly the failure modes you would expect at scale: gaps in verifying who is qualified for what, hazard information that moves too slowly, and processes that leave no clean audit trail behind them. The business consequence is not abstract. On a construction site, a gap in safety verification is an increase in the risk of an accident. Closing those gaps, and making the whole process auditable, was the reason for the project.

Pretius delivered a dedicated mobile EHS application for iOS and Android that took the core safety processes off paper and made them digital, fast, and, crucially, resilient to the absence of a network. Workers are verified in seconds by scanning QR codes. Daily briefings run entirely offline. Photos and video can be captured as evidence directly at the scene of an event. And when connectivity returns, an automatic synchronization module reconciles all of it back to the central systems without anyone having to think about it.

The app was built to integrate with the client's internal engineering and partner systems and to fit the company's specific data model, so that the digitized safety process and the existing workforce and permit systems operated as one. It runs on Microsoft Azure. The scope was deliberately bounded: work on the client's separate infrastructural and external systems was kept outside the project, so the effort stayed focused on the safety application itself.

The engagement ran for about six months on a fixed-price model, moving through analysis, development, a week of user acceptance testing, stabilization, and production rollout. A full-time, seven-person core team delivered it, and the collaboration later extended into additional commissioned work covering areas such as contractor-data snapshots and training statuses.

A field application like this meets obstacles that never appear in an office system, and the team planned for the ones that mattered.

The client did not need a generic safety app. It needed to digitize briefings, verify a huge and shifting workforce in seconds, and capture real evidence from the field, all on construction sites where the network frequently isn't there, and all wired into the company's own workforce and permit systems. By building the app in Flutter for a single cross-platform codebase, backing it with a Hive local database and an automatic synchronization module for genuine offline resilience, securing it with Keycloak, and running it on Azure, Pretius delivered exactly that.

The result improved safety across dozens of sites, sped up daily briefings, cut the errors of manual handling, and proved itself in formal audits, all while integrating deeply with the systems the client already relied on. For any organization whose work happens where connectivity can't be assumed, this project makes the case that offline-first is not a limitation to design around but a capability to build on.