Civil Engineering Reference
In-Depth Information
8.2.2 Hot works
Operations such as the laying of bitumen in fl at
roofi ng operations requires a bitumen boiler which is
powered by LPG and can pose a signifi cant risk if not
managed effectively; this also falls under the title of hot
work operations.
The use of bitumen or tar boilers can present a
signifi cant risk. Such fi res are invariably due to:
Generally the term 'hot work' applies to the use of open
fl ames, fi res and work involving the application of heat
by means of tools or equipment.
More specifi cally hot work includes any works
involving the use of naked fl ames, such as when welding
or brazing, or when undertaking plumbing work with gas
torches. Hot work also includes the use of grinders which
create high temperature sparks and also includes the use
of hot air guns for sealing materials such as fl ooring.
The use of naked fl ames and tools that apply heat,
in themselves will not necessarily be the cause of fi re,
but the inappropriate use of the equipment or lack of
control of combustible materials, fl ammable vapours,
etc. when undertaking hot work operations have been
the start of many fi res within the construction and
maintenance sector.
Sparks, for instance, falling on unprotected wood
or behind panelling or onto wood shavings or dust can
ignite the material. It has also been known that the heat
generated by hot air guns when laying fl ooring mater-
ials can ignite combustible items upon which the fl ooring
is being laid particularly as the heat generated in the
process is then sealed in.
It is often the case that sparks of heat generated in
such ways may go unnoticed for long periods of time
and given the correct conditions, perhaps opening
up sheeted areas, etc., will provide additional oxygen
supplies to complete the fi re triangle. Fires can start in
this way as long as 1-2 hours have elapsed after the
works have been completed.
Open fi res such as bonfi res to burn site rubbish
are to all intents and purposes banned in construction
operations due to fi re risk; however there are a variety of
different ways that naked fl ames can start a fi re.
➤
Poorly maintained equipment (thermostat faulty or
poorly adjusted)
➤
Poor position of the boiler such as on the roof itself
with no fi re resistant materials between it and the
roof
➤
Poorly supervised units allowing the boiler to boil
over or boil dry
➤
Attempting to move boilers while the burner is still
alight
➤
Overfi lling of the boiler allowing the boiler to boil
over
➤
Use of LPG cylinders without the appropriate safety
features such as fl ashback arrestors.
The use of oxy-fuel equipment such as acetylene and
propane are inevitably responsible for a number of fi res
in construction and maintenance operations. Many
of the key causes have already been discussed in this
chapter such as poor maintenance, use in close proxim-
ity to combustibles, fl ammables, etc.
The additional risks that the use of such equipment
brings arise from such issues as poor handling and
storage arrangements for cylinders of acetylene.
Acetylene is an extremely fl ammable gas. It is different
from other fl ammable gases because it is also unstable.
Under certain conditions, it can decompose explosively
into its constituent elements, carbon and hydrogen.
This decomposition can be more readily brought about
from mishandling, dropping, etc. of the cylinder causing
damage to the internal mass. Uncontrolled leaks from the
acetylene cylinder regulator or hoses can also have the
same effect.
Additionally the contamination of oxygen supplies
(cylinder, valve, regulator, hoses, etc.) by oil or grease
also has the capability of causing an explosion.
8.2.3
Flammable and combustible substances
The use, storage, transportation and disposal of fl amma-
ble and combustible substances within construction and
maintenance operations bring with them a wide variety
of different hazards and associated risks.
While the industry is attempting to reduce the use
of fl ammable substances as a matter of overall risk
management many proprietary substances used in the
work cannot be substituted.
Figure 8.7
Oxy-fuel equipment on a construction site
