Health Technical Memorandum 05-03 Part J – Fire Engineering in Healthcare Premises Guidance
Health Technical Memorandum 05-03: Operational provisions, Part J: Guidance on fire engineering of healthcare premises is a best-practice document issued by the Department of Health - Estates & Facilities Division in the United Kingdom. Published in January 2008, it forms part of the Firecode suite, a regulatory framework specifically tailored to fire safety within the National Health Service (NHS). This memorandum sits alongside other core documents such as HTM 05-02, which addresses functional provisions for healthcare premises, and builds upon the requirements of Approved Document B of the Building Regulations.
The scope of this guidance covers the application of fire-safety engineering principles to new healthcare buildings, extensions, alterations, and the change of use of existing structures into healthcare facilities. It outlines a performance-based approach as an alternative to prescriptive codes, particularly for complex or innovative designs where standard solutions may be restrictive or unnecessarily costly. The document is structured into chapters covering the definition of fire engineering, the Qualitative Design Review (QDR) process, fire growth, smoke spread and control, structural protection, and human factors. It also references BS 7974: 2001, the code of practice for the application of fire-safety engineering principles to the design of buildings.
This technical guide identifies the interactions between physical fire precautions, patient dependency, and management policies. It defines specific technical terms such as Available Safe Egress Time (ASET), Required Safe Egress Time (RSET), and Progressive Horizontal Evacuation (PHE), providing a framework for practitioners to demonstrate that alternative fire-safety packages meet functional safety objectives.
Qualitative Design Review (QDR) and Assessment
The fire-safety design process begins with a Qualitative Design Review (QDR). During this stage, the scope and objectives are defined, and performance criteria are established. For large projects, the QDR involves a group including the design team, fire-safety engineers, building control officers, and the trust fire adviser.
- Comparative criteria: Demonstrating a level of safety comparable to prescriptive methods such as Approved Document B.
- Deterministic criteria: Showing specific safety conditions are met, such as ensuring a smoke layer never drops below a specified height.
- Probabilistic criteria: Ensuring the probability of a fire event is below a defined frequency.
Following the QDR, a quantitative analysis is performed. The results are compared against the original criteria in an assessment stage. If the design fails, it must be modified and the cycle repeated until a successful design is determined.
Fire Growth and Design Fire Parameters
Characterising the Design Fire is a critical component of the fire engineering process. The size of a fire is expressed via the Heat Release Rate (HRR), measured in kilowatts (kW) or megawatts (MW). For the growth phase, a t-squared fire-growth curve is often used as a convenient approximation.
- HRR per unit area (Q/A): Should normally range between 250–2000 kW m–2 for building materials.
- Vitiated fires: Occur when oxygen supply is restricted, leading to lower heat release but potentially higher toxic hazards.
- Flashover: A sudden transition from a localised fire to the ignition of all exposed flammable surfaces within an enclosure.
- Backdraught: A hazard where the sudden introduction of oxygen into a ventilation-controlled fire causes rapid combustion of fuel vapours.
Occupant Classification and Human Factors
Fire safety in healthcare is heavily dependent on the mobility and dependency of patients. Occupants are classified into three distinct categories to assist designers in determining appropriate safety measures.
- Independent: Patients able to leave the premises without staff assistance or those who can negotiate stairs with minimal aid and comprehend signage.
- Dependent: Patients requiring staff assistance for evacuation; most patients fall into this category unless otherwise classified.
- Very high dependency: Patients in critical care, operating theatres, or areas where evacuation would be life-threatening.
The design assumes no reliance on external rescue by fire-and-rescue services. Occupants must be moved to a place of safety (such as an adjoining compartment) with assistance from staff only. Calculations must account for Pre-movement time, which includes time for fire detection, alarm recognition, and response.
Smoke Control and Ventilation Systems
Effective smoke management is required to ensure that the Available Safe Egress Time (ASET) exceeds the Required Safe Egress Time (RSET). Systems often include Smoke and Heat Exhaust Ventilation Systems (SHEVS) and the use of Smoke reservoirs.
- Smoke curtains: Fail-safe devices used to channel smoke into reservoirs, designed to withstand temperatures exceeding 200°C.
- Replacement air: An adequate supply of make-up air is necessary for extraction systems to function; airflow velocity in escape routes should remain below 3 m/s.
- Stack effect: A consideration for tall hospital buildings where pressure differences affect smoke movement.
- Plugholing: A phenomenon where excessive localised extraction draws air from low levels through the smoke layer, reducing system efficiency.
Structural Fire Protection
Structural fire protection aims to prevent collapse and the spread of fire between compartments. Performance is measured against three primary criteria: Stability (avoidance of collapse), Integrity (avoidance of cracks), and Insulation (restricting temperature rise on the unexposed face).
- Fire resistance time: A comparative measure from standard tests, not the actual survival time in a real fire.
- Time-equivalent exposure: A method to express fire severity in terms of equivalent exposure to a standard fire curve.
- Parametric curves: Validated for compartments of moderate size (~100 m2 floor area) with predominantly cellulosic fuels.
Frequently Asked Questions
What is the definition of a competent person under HTM 05-03 Part J?
A competent person is defined as someone with sufficient technical training and actual experience to understand the dangers involved and properly undertake the fire-safety measures referred to in the document.
What is Progressive Horizontal Evacuation (PHE)?
PHE is the evacuation of patients away from a fire into a fire-free compartment or sub-compartment on the same level, ensuring they reach a place of relative safety without changing floors.
How are ASET and RSET used in fire-safety engineering?
Available Safe Egress Time (ASET) is the time until conditions become untenable, while Required Safe Egress Time (RSET) is the time needed for occupants to escape. The safety objective is to ensure that ASET is greater than RSET.
What is a Hospital Street?
A hospital street is a special type of compartment connecting final exits, stairway enclosures, and department entrances, serving as a fire-fighting bridgehead and safe evacuation route.
When should fire engineering be applied to healthcare premises?
It is mainly applied when designs are complex or innovative, when existing codes restrict flexibility, or when prescriptive solutions are unnecessarily costly, such as in high-rise hospitals or atria.
What are the tenability criteria for smoke in hospital wards?
In areas with dependent or very high dependency patients, there should be no smoke obscuration or concentration at head height, as these patients cannot self-rescue and may experience high anxiety.
Does HTM 05-03 Part J replace prescriptive guidance?
No, it builds on prescriptive guidance like HTM 05-02 and is intended as an alternative, performance-based approach for situations where the prescriptive 'Firecode' solutions are not appropriate.
What is the purpose of a Qualitative Design Review (QDR)?
The QDR is the initial stage of the design process where the scope, objectives, potential fire scenarios, and performance criteria are defined and agreed upon by stakeholders.
