Chapter 3

A significant quantity of the chemicals supplied to the well site are used during
drilling operations. The drilling mud used in these operations contain some amount of
additives or chemicals that are harmful when an operator is exposed or come in contact.
The severity and the type of health effects depend on factors such as the dosage, duration,
the route of exposure or the pathway such as inhalation, dermal or skin, oral and the likes
by which an operator is exposed. This chapter therefore reviews the potential areas of
drilling fluids exposure and its associated health effects encountered during a typical
onshore and offshore drilling operations.
Potential Areas of Drilling Fluid Exposure
The likely exposure types encountered in a typical drilling environment during
drilling operation includes the following.
Drilling Floor
Shale Shaker House
Mud Pit System
Deck Operations
Sack Room
Mixing Hopper etc.
3.2.1 Drilling Floor
The Drill Floor is the heart of any drilling rig and is also known as the pad. This is
the area where the drill string begins its trip into the earth. It is traditionally where joints of
pipe are assembled, as well as the bottom hole assembly (BHA), drilling bit, and various
other tools. This is the primary work location for roughnecks and the driller
(', 2009).
Contact with drilling fluids as well as lubricants, pipe dope, hydraulic oils, etc. by
roughnecks and other personnel on the drill floor is predominantly dermal contact. This
can be prolonged and repetitive due to the manual nature of the work involved. In most
cases contact may be through manual handling of unclean pipes during breaking out of
pipes, preparing to break out pipes, handling of tubular, lowering of drill pipe, sprays, and
spills from cleaning operations and high pressure washing (Fig 3.1, OSHA 2009a).
Fig.3.1 Setting Slip and Lowering Drill Pipe (OSHA, 2009a)
Fig.3.2 Breaking Out Pipe (OSHA, 2009a)
Fig.3.3 Making up Mousehole Joint and Applying Pipe Dope to a Connection
(OSHA, 2009a)
3.2.2 Shale Shaker House
According to Robinson et al. (1999), the purpose of shale shaker is to remove from
the mud dirt the rock drilled by the bit (Figs.3.4a and 3.4b, Robinson et al.,1999). High
hydrocarbon mist and vapour exposure levels have been reported in shale shaker rooms.
Workers may be exposed to drilling fluids either by inhaling aerosols and vapours or by
skin contact. Main exposure opportunities are:
Washing with high-pressure guns using a hydrocarbon-based fluid.
Cleaning and changing screens.
Checking the shaker screens for wear.
Solid and Liquid separation.
Mechanical Agitation of the Shale (Steinsvag et al., 2005; James et al., 1999).
(Robinson et al.,1999)
Fig.3.4b Shale Shaker House (Saleem and Ross , 2009).
3.2.3 Mud Pit System
The mud is monitored throughout the drilling process. A mud engineer and or the
Derrickman may periodically check the mud by measuring its viscosity, density, and other
properties. The mud engineer can be exposed to burns, or physical injury caused by
contact with skin or eyes. Persons in the area are generally needed to perform less
complicated tasks but on regular basis with the potential of inhalation hazard and also
explosions or violent reactions from chemical mixed improperly (Fig. 3.5, OSHA, 2009a).
Fig. 3.5 Mud Pit System (OSHA, 2009a)
3.2.4 Deck Operations
Exposure can occur through contact with contaminated surfaces, spilled materials,
handling of drilling fluid contaminated wastes, e.g. cutting containment and or
transportation systems regulations require the use of fume hoods and extract ventilation
systems in the fluids testing laboratory (OGP and IPIECA, 2009).
3.2.5 Sack Room
Gardener (2003), reported that although base oils have attracted the most attention,
workers are potentially exposed to a range of particulates, especially during powder
handling of various additives especially barium sulphate in the sack room. The handling of
these various powdered products can cause exposure of mud engineers and other operators
in the sack room to both skin contact and inhalation (Figs. 3.6a, and 3.6b, Robinson et
In practice, the potential problems of exposure and the opportunities for control are
much the same as in comparable situations onshore. For instance, over the working period,
exposures to barium sulphate during the manual emptying of sacks can easily reach 5–10
times the Occupational Exposure Limit (OEL).
Fig 3.6a Sack Room-Additives Mixing (Saleem and Ross , 2009).
Fig 3.6b Sack Room-Additives Mixing (Saleem and Ross , 2009).
3.2.6 Mud Laboratory
According to OSHA (2009a), personnels or mud engineers are exposed to drilling
fluids during sampling or testing of the mud. The sampling process from a mud pit or flow
line requires the use of various forms of testing equipment to gain the necessary
information about the fluid for analysis and remedial treatment purposes. One testing unit
operates at high temperature to boil off the fluid fractions oil and water. This test creates
gases which can be uncomfortable to a person in the non-vented vicinity.
3.2.7 Mixing Hopper
The mixing hopper also provides an opportunity for exposure to chemicals like
caustic soda, xc polymer, calcium chloride etc. as this is the point at which powdered
products or liquid additives are introduced to the operation through a conical shaped
device (Fig. 3.7; OSHA, 2009a). Typically the narrow bottom section of the cone has a
fluids circulating pipe passing through it. A choke provides a jetting action within the pipe
which draws the materials added into the fluid being circulated. The products and the
associated additives are usually handled manually at the hopper .This can give rise to dust
or splashing. Both of these conditions are potentially hazardous. More modern facilities
enable powdered products such as barite, hematite, calcium chloride, etc. to be handled
mechanically even to the point of removing and disposing of the packaging. Liquid
additives such as glycols, fatty-acid soap, resin acids etc. can be pumped into the hopper
instead of manually poured. The handling of powdered sacked products and liquid
products such as caustic soda from drums or cans, and the mixing of bulk powders such as
barite, carboxymaethylcellulose, xanthan gum etc. can cause exposure.
Primarily this will be inhalation exposure as there may be dust associated with the
movement of products in the storage area or with mixing products into the hopper.
However, skin contact can also occur, particularly with powdered materials (OGP and
IPIECA, 2009).
Fig. 3.7 Additive Mixing Hopper (OSHA, 2009a)
3.2.8 Laundry
Ineffective cleaning of personal protective equipment may leave residues of
drilling fluids on the clothes which may be exposed to the skin. Cauchi (2004), reported
that detergent used by the rig laundry service may not be efficient or adapted to remove
Oil Base Mud (OBM) or Non- Aqueous Drilling Fluid (NADFs) derivatives from the
protective clothing, resulting in chemical accumulation into the clothing fibers.
Duration of Exposure
One of the most influential factors in personal exposures is the duration of
exposure. The duration of exposure can be significantly increased by the contamination of
inappropriate protective equipment, which may actually prolong contact with
contaminants, particularly for dermal exposure, e.g. fabric gloves soaked in hydrocarbon
or impermeable gloves contaminated on the inside. Appendices 1, 2, 3, 4, 5 and 6 contain
information on likely exposure types and durations for these and other key tasks typically
encountered in a drilling operation, as well as factors which may influence the level of
exposure (OGP and IPIECA, 2009).
Health Effect Associated with Drilling Fluids Contact
The risk of adverse health effects from drilling fluids is determined by the
hazardous components of the fluids, additives and by human exposure to those
components. According to OHS (2009), skin irritation and contact dermatitis are the most
common health effects observed from drilling fluids exposure in human beings, with
headache, nausea, eye irritation, and coughing seen less frequently. The effects are caused
by the physico-chemical properties of the drilling fluid as well as the inherent properties of
drilling fluid additives, and are dependent on the route of exposure such as dermal,
inhalation, oral and others (Fig. 3.8, OGP AND IPIECA, 2009).
Conditions of use, Control
Measures and physical
Protective equipment
Drilling fluid composition
and physical form of
Worker or Individual
Variable Susceptibility
Depends mainly on hazards
and exposure route
and conditions
Fig.3.8 Relationship between Health Hazard, Exposure and Effects
(Modified after OGP AND IPIECA, 2009)
API (1998), also reported that the majority of health hazard associated with drilling
fluids arise from manual handling of mud or drilling fluid additives, and exposure to the
mud and particular drilling components. Exposure to constituent chemicals and derivative
compound poses a health risk in many cases if appropriate controls are not in place.
Exposure may be through inhalation, dermal contacts or ingestion. Most solid additives
are in the form of fine powders, and present an inhalation hazards. In many cases nuisance
dust limits apply, but the potential for exposures up to and beyond the limit occur. Liquid
component pose a dermal exposure hazard during formulation and drilling (during with
there is also risk of ingestion), and there is a risk of inhalation exposure where sprays,
mists or vapour are formed. The vapour pressure and the flash point of the base oils is
critical to the vapour concentration and fire risk in enclosed spaces such as around shale
shakers and mud pits.
API (1998) and OSHA (2009a), reported the major routes of drilling fluids
exposure as:
Inhalation Exposure
Dermal Exposure
Oral Exposure and others
3.4.1 Inhalation Exposure
Gardener (2003), reported that the potential chemical changes in muds during use
and recycling can result in more toxic substance being released. Since muds are subjected
to elevated temperatures and increased pressures, there has been a concern that organic
components might break down, or chemical reactions might occur, to form more toxic
substances. There was a particular concern that base oil high in aromatics might contain,
or form polycyclic aromatic hydrocarbons (PAHs), while muds based on alkyl benzenes
might break down to yield free benzene.
According to Gardener (2003), there is no evidence as to the limit of PAH contents.
However the current guidelines for the UK Revised Offshore Chemical Notification
Scheme (CEFAS, 2002) do require a full declaration of PAH content using methods that
can achieve a limit of detection of ~0.1 ppm. OGP AND IPIECA (2009) also reported on
the limitation of the detailed composition and size of the aerosol droplets.
OGP AND IPIECA (2009), reported that drilling fluids are often circulated in an
open system at elevated temperatures with agitation that can result in a combination of
vapours, aerosol and/or dust above the mud pit. In the case of water-based fluids the
vapours comprise steam and dissolved additives. In the case of non-aqueous drilling fluids
the vapours can consist of the low boiling-point fraction of hydrocarbons (paraffins,
olefins, naphthenes and aromatics), and the mist contains droplets of the hydrocarbon
fraction used. This hydrocarbon fraction may contain additives, sulphur, mono-aromatics
and/or polycyclic aromatics. It should be noted that although the hydrocarbon fraction
may contain negligible amounts of known hazardous constituents such as Benzene,
toluene, ethylbenzene and xylenes (BTEX) at low boiling point, these will evaporate at
relatively higher rates potentially resulting in higher concentrations in the vapour phase
than anticipated.
McDougal et al. (2000), also reported that petroleum distillates such crude oil,
diesel oil (Group I-Non Aqueous Fluids) have been associated with renal, hepatic,
neurologic, immunologic, and pulmonary toxicity when there are inhaled or ingested and
they are also irritating to the skin and mucus membrane. ATSDR (1999a) reported some
health effects associated with inhalation exposure as:
Neurological Effects
Hematological Effect,
Immunological Effect
Lymphoreticular Effects
Pulmonary Effects
Neurological Effects
All the BTEXs cause neurological effects. Neurological effects are the basis for
Minimal Risks Levels for both acute and chronic exposures to toluene (ATSDR, 2000) and
mixed xylenes, and for intermediate exposures to benzene; neurological effects are not as
sensitive for ethylbenzene (ATSDR,1999b; Appendices 11 and 12 present the Lowest
Observed Adverse Effect Level (LOAEL) for mixed xylene and ethylbenzene). The
neurological effects consist primarily of central nervous system depression. Toluene’s
neurotoxicity also includes ototoxicity. Evidence of hearing loss has been seen in both
occupationally exposed humans and in animals. There is limited evidence that chronic
inhalation exposure to benzene may affect the peripheral nervous system; this evidence is
from a single study of occupationally exposed humans who also had aplastic anemia
(ATSDR, 1999a).
According to OGP and IPIECA (2009), inhalation of high concentrations of
hydrocarbons may result in hydrocarbon induced neurotoxicity (Breathing toluene at
concentrations greater than 100 parts per million for more than several hours can cause
fatigue, headache, nausea, and drowsiness, ATSDR(1999a)), a non-specific effect resulting
in headache, nausea, dizziness, fatigue, lack of coordination, problems with attention and
memory, gait disturbances and narcosis. These symptoms are of a temporary nature and
are only observed at extremely high concentrations. Other symptoms also include limb
(, 2009; Appendix 10 presents LOAEL for
Exposure to high levels of n-hexane may result in peripheral nerve damage, called
“peripheral neuropathy” characterized by numbness in the feet and legs and, in severe
cases,paralysis. This has occurred in workers exposed to 500-2,500 ppm (parts per
1999c;, 2009).
Hematological, Immunological and Lymphoreticular Effects
Benzene is the only BTEX that has well characterized hematological,
immunological, and lymphoreticular effects in humans (and animals) at low levels of
inhalation exposure. Immunological and Lymphoreticular effects are the basis for the
derivation of the acute inhalation Minimal Risk Level (MRL) for benzene. Benzene affects
hematopoiesis, decreasing the production of all major types of blood cells, and can also
cause hyperplasia. Developmental effects are the basis for intermediate Minimal Risk
Levels (MRLs) for ethylbenzene and mixed xylene, indicating that the embryo/fetus may
be particularly sensitive to these two BTEXs (ATSDR, 1999a; ATSDR, 1997). Appendix
10 presents the Lowest Observed Adverse Effect Level (LOAEL) for benzene.
Carcinogenic Effects
Benzene is considered to be carcinogenic to humans by the inhalation route of
exposure. Occupational exposure to benzene was associated within increased incidences
of nonlymphocytic leukemia. Studies in animals also found increased incidences of
neoplasia in animals treated by inhalation or gavage with benzene (ATSDR, 1999c).
OGP and IPIECA (2009), also reported that olefins, esters and paraffins commonly
used in drilling fluids (Group III, negligible-aromatic content fluids) do not contain
specific carcinogenic compounds and are not carcinogenic in animal tests. These
compounds are not therefore associated with tumour formation upon dermal exposure.
However, Group I (high-aromatic content fluids), especially diesel fuel, can contain
significant levels of PAH. Diesel fuels that contain cracked components may be genotoxic
due to high proportions of 3-7 ring PAH. Although no epidemiological evidence for diesel
fuel carcinogenicity in humans exists, skin-painting studies in mice show that long-term
dermal exposure to diesel fuels can cause skin tumours, irrespective of the level of PAH.
This effect is attributed to chronic irritation of the skin. In humans, chronic irritation may
cause small areas of the skin to thicken, eventually forming rough wart like growth which
may become malignant
Pulmonary Effects
According to OGP and IPIECA (2009), the most commonly observed symptoms in
workers exposed to NADF and aqueous fluid aerosols are cough and phlegm.
Epidemiological studies of workers exposed to mist and vapour from mineral oils
indicated increased prevalence of pulmonary fibrosis. More recent inhalation toxicology
studies show that exposures to high concentrations of aerosols from mineral-based oils
resulted mainly in concentration-related accumulation in the lung of alveolar macrophages
laden with oil droplets. Inflammatory cells were observed with higher aerosol
concentrations, consistent with the clinical literature from highly exposed workers.
These pulmonary response to the presence of deposited aerosol are not related to
vapour exposure. The results on various petroleum mineral oils support the American
Conference of Government Industrial Hygiene Threshold Limit Value (ACGIH® TLV,
1996) of 5 mg/m3 for mineral-oil mist. It should be noted that extremely high
concentrations of low viscosity hydrocarbon aerosols can either be aspirated, or be
deposited in droplets in the lungs, causing chemical pneumonitis potentially resulting in
pulmonary oedema, pulmonary fibrosis and, in occasional cases, death. In some cases,
occupational exposure to drilling fluids is associated with respiratory irritation. It is likely
that this is caused by additives in the drilling fluid and/or the physico-chemical properties
as water-based drilling fluids have a typical pH of 8.0–10.5.
An issue indirectly related to health, but directly related to the working
environment is the odour of drilling fluids. Some drilling fluids may have an objectionable
odour caused by the main constituents or specific additives. During operations the drilling
fluids may be contaminated with crude oil and drilling cuttings, which may change the
odorous properties of the drilling fluid. Measurements changes appeared to be a nonspecific of head space volatiles during drilling operations have indicated the presence of,
amongst others, dimethyl sulphide and isobutyraldehyde. Both compounds have a pungent
odour and may create unpleasant working conditions (OGP and IPIECA, 2009).
According DCC (2009), prolonged excessive inhalation of isobutanol or
isobutyraldehyde may result in adverse effects. Symptoms of excessive exposure may be
anesthetic or narcotic effects and dizziness or drowsiness. Isobutanol cause central
nervous system effects. EA (2009a) also reported that excessive exposure to
isobutyraldehyde may affect the brain, digestive system, eye, lung, nose, skin and throat.
Dimethyl sulphate may cause cancer and genetic damage. Excessive exposure to Dimethyl
sulphate may affect the brain, digestive system, eye, kidney, liver, lung, skin, throat and
the unborn child (EA, 2009b).
3.4.2 Dermal Exposure
Most chemicals are readily absorbed through the skin and can cause other health
effects and/or contribute to the dose absorbed by inhalation of the chemical from the air.
When drilling fluids are circulated in an open system with agitation, there is a high
likelihood of dermal exposure. The potential dermal exposure is not limited to the hands
and forearms, but extends to all parts of the body. Actual exposure depends on the drilling
fluid system and the use of personal protection equipment (PPE). Many studies indicate
that absorption of chemicals through the skin can occur without being noticed by the
worker. In many cases, skin is a more significant route of exposure than the lung (OSHA,
Dermatitis and Irritation
Skin contact with drilling fluids or mud can also cause inflammation of the skin,
referred to as dermatitis. Signs and symptoms of dermatitis can include itching, redness,
swelling, blisters, scaling, and other changes in the normal condition of the skin (Fig. 3.9;, 2009). On the drill floor,
in particular, skin contamination can be extensive, but occasionally dermatitis also occurs
in divers who make contact with discarded cuttings on the sea bed (Ormerod et al., 1998).
Upon dermal exposure to drilling fluids, the most frequent reported effects are skin
irritation and contact dermatitis (Fig. 3.9, 2009). Contact dermatitis is one of the most common chemicallyinduced occupational illnesses probably accounting for 10-15 percent of all occupational
illness. Symptoms and seriousness of the condition vary and are dependent on the type
and length of fluid and the susceptibility.
Fig. 3.9 Dermatitis of the Hands (, 2009)
Petroleum hydrocarbons will remove natural fat from the skin, which results in drying and
cracking. These conditions allows compounds to permeate through the skin leading to skin
irritation and dermatitis. Some individuals may be especially susceptibility to these effects.
Skin irritation can be petroleum hydrocarbons, specifically with aromatics and C8-C14
paraffins. Petroleum streams containing these compounds, such as kerosene and diesel
(gas oil), are clearly irritating to skin. This is suggested to be become malignant caused by
the paraffins, which do not readily penetrate the skin but are absorbed into the skin, hereby
causing irritation (McDougal, 2000). Linear alpha olefins and esters commonly used in
drilling fluids are only slightly irritating to skin, whereas linear internal olefins are not
irritating to skin.
In addition to the irritancy of the drilling fluid hydrocarbon constituents, several
drilling fluid additives may have irritant, corrosive or sensitizing properties (Cauchi, 2004)
For example calcium chloride has irritant properties and zinc bromide is corrosive whereas
a polyamine emulsifier has been associated with sensitizing properties. Although waterbased fluids are not based on hydrocarbons, the additives in the fluid may still cause
irritation or dermatitis. Excessive exposure under conditions of poor personal hygiene may
lead to oil acne and folliculitis (OGP and IPIECA, 2009)
ATSDR (1997) concluded that it is reasonable to expect that adverse hematological
and immunological effects might occur following dermal exposure to benzene, because
benzene is absorbed through the skin and absorption through any route would increase the
risk of these effects.
3.4.3 Oral Exposure.
As drilling fluids are not intended for ingestion, oral exposure is unlikely and
negligible as compared to the other routes of exposure. Oral exposure may occur when
hands are not properly washed before they are used to handle for or to smoke.
Data for the oral route of exposure are less extensive. The BTEXs cause
neurological effects, generally central nervous system depression, by the oral route. This is
a sensitive effect for toluene and p-xylene, for which it is the basis of acute and/or
intermediate Minimal Risks Levels (MLs). Renal and hepatic effects are also seen with
oral exposure to these compounds. Renal effects are the basis for the intermediate. MRL
for mixed xylenes and hepatic effects are the basis for the intermediate MRL for m-xylene.
The hepatic effects tend to be mild, including increased liver weight and cytochromes.
Benzene causes hematological effects by the oral route that are similar to those seen from
inhalation exposure (ATSDR, 1999a). Appendices 13, 14 and 15 presents the LOAEL.
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